hwasan: Improve precision of checks using short granule tags.

[pcc]

Summary

A short granule is a granule of size between 1 and TG-1 bytes. The size
of a short granule is stored at the location in shadow memory where the
granule's tag is normally stored, while the granule's actual tag is stored
in the last byte of the granule. This means that in order to verify that a
pointer tag matches a memory tag, HWASAN must check for two possibilities:

• the pointer tag is equal to the memory tag in shadow memory, or
• the shadow memory tag is actually a short granule size, the value being loaded is in bounds of the granule and the pointer tag is equal to the last byte of the granule.

Pointer tags between 1 to TG-1 are possible and are as likely as any other
tag. This means that these tags in memory have two interpretations: the full
tag interpretation (where the pointer tag is between 1 and TG-1 and the
last byte of the granule is ordinary data) and the short tag interpretation
(where the pointer tag is stored in the granule).

When HWASAN detects an error near a memory tag between 1 and TG-1, it
will show both the memory tag and the last byte of the granule. Currently,
it is up to the user to disambiguate the two possibilities.

Because this functionality obsoletes the right aligned heap feature of
the HWASAN memory allocator (and because we can no longer easily test
it), the feature is removed.

Also update the documentation to cover both short granule tags and
outlined checks.

[pcc]

• Simplify tagAlloca

[eugenis]

compiler-rt/lib/hwasan/hwasan_allocator.cpp

159–160

When !(flags()->tag_in_malloc && malloc_bisect(stack, orig_size)), the tail tag should be 0 as well.

compiler-rt/lib/hwasan/hwasan_checks.h

69

s/15/kShadowAlignment -1/

113

0xfull, nice :)
A named constant please.

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

1197

Good. I think we will need to do the same in MTE patches, but for different reason.

There is something in BasicAA that thinks that a store of size 16 (in MachineInstr) can not possibly alias with a smaller alloca, so simply increasing alloca alignment is not enough.

[pcc]

• Address review comments

compiler-rt/lib/hwasan/hwasan_allocator.cpp

159–160

It was already being set to 0 on line 167. You mean that the tag in shadow memory should be 0, right? Makes sense, done.

[eugenis]

LGTM

[xiangzhangllvm]

compiler-rt/trunk/lib/hwasan/hwasan_checks.h

76 ↗

(On Diff #208794)

Hello @pcc I think here seems some problem, the ptr is user passing point,
*(ptr + n) should have the user's real data. it shouldn't "== ptr_tag".

[pcc]

compiler-rt/trunk/lib/hwasan/hwasan_checks.h

76 ↗

(On Diff #208794)

If this is a short granule then from the user's perspective the maximum size of the granule is (granule size - 1). This means that the last byte of the granule is free for us to use to store the granule's real tag.

clang/docs/HardwareAssistedAddressSanitizerDesign.rst

 * For every such object a random `TS`-bit tag `T` is chosen (`TS`, or tag size, is e.g. 4 or 8)
 * The pointer to the object is tagged with `T`.
 * The memory for the object is also tagged with `T` (using a `TG=>1` shadow memory)
 * Every load and store is instrumented to read the memory tag and compare it
   with the pointer tag, exception is raised on tag mismatch.
 
 For a more detailed discussion of this approach see https://arxiv.org/pdf/1802.09517.pdf
 
+Short granules
+--------------
+
+A short granule is a granule of size between 1 and `TG-1` bytes. The size
+of a short granule is stored at the location in shadow memory where the
+granule's tag is normally stored, while the granule's actual tag is stored
+in the last byte of the granule. This means that in order to verify that a
+pointer tag matches a memory tag, HWASAN must check for two possibilities:
+
+* the pointer tag is equal to the memory tag in shadow memory, or
+* the shadow memory tag is actually a short granule size, the value being loaded
+  is in bounds of the granule and the pointer tag is equal to the last byte of
+  the granule.
+
+Pointer tags between 1 to `TG-1` are possible and are as likely as any other
+tag. This means that these tags in memory have two interpretations: the full
+tag interpretation (where the pointer tag is between 1 and `TG-1` and the
+last byte of the granule is ordinary data) and the short tag interpretation
+(where the pointer tag is stored in the granule).
+
+When HWASAN detects an error near a memory tag between 1 and `TG-1`, it
+will show both the memory tag and the last byte of the granule. Currently,
+it is up to the user to disambiguate the two possibilities.
+
 Instrumentation
 ===============
 
 Memory Accesses
 ---------------
 All memory accesses are prefixed with an inline instruction sequence that
 verifies the tags. Currently, the following sequence is used:
 
-
 .. code-block:: none
 
   // int foo(int *a) { return *a; }
-  // clang -O2 --target=aarch64-linux -fsanitize=hwaddress -c load.c
+  // clang -O2 --target=aarch64-linux -fsanitize=hwaddress -fsanitize-recover=hwaddress -c load.c
   foo:
-       0: 08 00 00 90   adrp  x8, 0 <__hwasan_shadow>
-       4: 08 01 40 f9   ldr x8, [x8]          // shadow base (to be resolved by the loader)
-       8: 09 dc 44 d3   ubfx  x9, x0, #4, #52 // shadow offset
-       c: 28 69 68 38   ldrb  w8, [x9, x8]    // load shadow tag
-      10: 09 fc 78 d3   lsr x9, x0, #56       // extract address tag
-      14: 3f 01 08 6b   cmp w9, w8            // compare tags
-      18: 61 00 00 54   b.ne  24              // jump on mismatch
-      1c: 00 00 40 b9   ldr w0, [x0]          // original load
-      20: c0 03 5f d6   ret
-      24: 40 20 21 d4   brk #0x902            // trap
+       0: 90000008  adrp  x8, 0 <__hwasan_shadow>
+       4: f9400108  ldr x8, [x8]         // shadow base (to be resolved by the loader)
+       8: d344dc09  ubfx  x9, x0, #4, #52  // shadow offset
+       c: 38696909  ldrb  w9, [x8, x9]     // load shadow tag
+      10: d378fc08  lsr x8, x0, #56      // extract address tag
+      14: 6b09011f  cmp w8, w9           // compare tags
+      18: 54000061  b.ne  24 <foo+0x24>    // jump to short tag handler on mismatch
+      1c: b9400000  ldr w0, [x0]         // original load
+      20: d65f03c0  ret
+      24: 7100413f  cmp w9, #0x10        // is this a short tag?
+      28: 54000142  b.cs  50 <foo+0x50>    // if not, trap
+      2c: 12000c0a  and w10, w0, #0xf    // find the address's position in the short granule
+      30: 11000d4a  add w10, w10, #0x3   // adjust to the position of the last byte loaded
+      34: 6b09015f  cmp w10, w9          // check that position is in bounds
+      38: 540000c2  b.cs  50 <foo+0x50>    // if not, trap
+      3c: 9240dc09  and x9, x0, #0xffffffffffffff
+      40: b2400d29  orr x9, x9, #0xf     // compute address of last byte of granule
+      44: 39400129  ldrb  w9, [x9]         // load tag from it
+      48: 6b09011f  cmp w8, w9           // compare with pointer tag
+      4c: 54fffe80  b.eq  1c <foo+0x1c>    // if so, continue
+      50: d4212440  brk #0x922           // otherwise trap
+      54: b9400000  ldr w0, [x0]         // tail duplicated original load (to handle recovery)
+      58: d65f03c0  ret
 
 Alternatively, memory accesses are prefixed with a function call.
+On AArch64, a function call is used by default in trapping mode. The code size
+and performance overhead of the call is reduced by using a custom calling
+convention that preserves most registers and is specialized to the register
+containing the address and the type and size of the memory access.
 
 Heap
 ----
 
 Tagging the heap memory/pointers is done by `malloc`.
 This can be based on any malloc that forces all objects to be TG-aligned.
 `free` tags the memory with a different tag.
 

compiler-rt/lib/hwasan/hwasan_allocator.cpp

 // HWAddressSanitizer allocator.
 //===----------------------------------------------------------------------===//
 
 #include "sanitizer_common/sanitizer_atomic.h"
 #include "sanitizer_common/sanitizer_errno.h"
 #include "sanitizer_common/sanitizer_stackdepot.h"
 #include "hwasan.h"
 #include "hwasan_allocator.h"
+#include "hwasan_checks.h"
 #include "hwasan_mapping.h"
 #include "hwasan_malloc_bisect.h"
 #include "hwasan_thread.h"
 #include "hwasan_report.h"
 
 #if HWASAN_WITH_INTERCEPTORS
 DEFINE_REAL(void *, realloc, void *ptr, uptr size)
 DEFINE_REAL(void, free, void *ptr)

 static const tag_t kFallbackFreeTag = 0xBC;
 
 enum RightAlignMode {
   kRightAlignNever,
   kRightAlignSometimes,
   kRightAlignAlways
 };
 
-// These two variables are initialized from flags()->malloc_align_right
-// in HwasanAllocatorInit and are never changed afterwards.
-static RightAlignMode right_align_mode = kRightAlignNever;
-static bool right_align_8 = false;
-
 // Initialized in HwasanAllocatorInit, an never changed.
-static ALIGNED(16) u8 tail_magic[kShadowAlignment];
+static ALIGNED(16) u8 tail_magic[kShadowAlignment - 1];
 
 bool HwasanChunkView::IsAllocated() const {
   return metadata_ && metadata_->alloc_context_id && metadata_->requested_size;
 }
 
 // Aligns the 'addr' right to the granule boundary.
 static uptr AlignRight(uptr addr, uptr requested_size) {
   uptr tail_size = requested_size % kShadowAlignment;
   if (!tail_size) return addr;
-  if (right_align_8)
-    return tail_size > 8 ? addr : addr + 8;
   return addr + kShadowAlignment - tail_size;
 }
 
 uptr HwasanChunkView::Beg() const {
   if (metadata_ && metadata_->right_aligned)
     return AlignRight(block_, metadata_->requested_size);
   return block_;
 }
void GetAllocatorStats(AllocatorStatCounters s) {
   allocator.GetStats(s);
 }
 
 void HwasanAllocatorInit() {
   atomic_store_relaxed(&hwasan_allocator_tagging_enabled,
                        !flags()->disable_allocator_tagging);
   SetAllocatorMayReturnNull(common_flags()->allocator_may_return_null);
   allocator.Init(common_flags()->allocator_release_to_os_interval_ms);
-  switch (flags()->malloc_align_right) {
-    case 0: break;
-    case 1:
-      right_align_mode = kRightAlignSometimes;
-      right_align_8 = false;
-      break;
-    case 2:
-      right_align_mode = kRightAlignAlways;
-      right_align_8 = false;
-      break;
-    case 8:
-      right_align_mode = kRightAlignSometimes;
-      right_align_8 = true;
-      break;
-    case 9:
-      right_align_mode = kRightAlignAlways;
-      right_align_8 = true;
-      break;
-    default:
-      Report("ERROR: unsupported value of malloc_align_right flag: %d\n",
-             flags()->malloc_align_right);
-      Die();
-  }
-  for (uptr i = 0; i < kShadowAlignment; i++)
+  for (uptr i = 0; i < sizeof(tail_magic); i++)
     tail_magic[i] = GetCurrentThread()->GenerateRandomTag();
 }
 
 void AllocatorSwallowThreadLocalCache(AllocatorCache *cache) {
   allocator.SwallowCache(cache);
 }
 
 static uptr TaggedSize(uptr size) {
static void *HwasanAllocate(StackTrace *stack, uptr orig_size, uptr alignment,
   meta->alloc_context_id = StackDepotPut(*stack);
   meta->right_aligned = false;
   if (zeroise) {
     internal_memset(allocated, 0, size);
   } else if (flags()->max_malloc_fill_size > 0) {
     uptr fill_size = Min(size, (uptr)flags()->max_malloc_fill_size);
     internal_memset(allocated, flags()->malloc_fill_byte, fill_size);
   }
-  if (!right_align_mode)
+  if (size != orig_size) {
     internal_memcpy(reinterpret_cast<u8 *>(allocated) + orig_size, tail_magic,
-                    size - orig_size);
+                    size - orig_size - 1);
+  }
 
   void *user_ptr = allocated;
   // Tagging can only be skipped when both tag_in_malloc and tag_in_free are
   // false. When tag_in_malloc = false and tag_in_free = true malloc needs to
   // retag to 0.
   if ((flags()->tag_in_malloc || flags()->tag_in_free) &&
       atomic_load_relaxed(&hwasan_allocator_tagging_enabled)) {
     tag_t tag = flags()->tag_in_malloc && malloc_bisect(stack, orig_size)
                     ? (t ? t->GenerateRandomTag() : kFallbackAllocTag)
                     : 0;
-    user_ptr = (void *)TagMemoryAligned((uptr)user_ptr, size, tag);
-  }
-
-  if ((orig_size % kShadowAlignment) && (alignment <= kShadowAlignment) &&
-      right_align_mode) {
-    uptr as_uptr = reinterpret_cast<uptr>(user_ptr);
-    if (right_align_mode == kRightAlignAlways ||
-        GetTagFromPointer(as_uptr) & 1) {  // use a tag bit as a random bit.
-      user_ptr = reinterpret_cast<void *>(AlignRight(as_uptr, orig_size));
-      meta->right_aligned = 1;
+    uptr tag_size = orig_size ? orig_size : 1;
+    uptr full_granule_size = RoundDownTo(tag_size, kShadowAlignment);
+    user_ptr = (void *)TagMemoryAligned((uptr)user_ptr, full_granule_size, tag);
+    if (full_granule_size != tag_size) {
+      u8 *short_granule = reinterpret_cast<u8 *>(allocated) + full_granule_size;
+      TagMemoryAligned((uptr)short_granule, kShadowAlignment,
+                       tag_size % kShadowAlignment);
+      short_granule[kShadowAlignment - 1] = tag;
     }
   }
 
   HWASAN_MALLOC_HOOK(user_ptr, size);
   return user_ptr;
 }
 
 static bool PointerAndMemoryTagsMatch(void *tagged_ptr) {
   CHECK(tagged_ptr);
-  tag_t ptr_tag = GetTagFromPointer(reinterpret_cast<uptr>(tagged_ptr));
+  uptr tagged_uptr = reinterpret_cast<uptr>(tagged_ptr);
   tag_t mem_tag = *reinterpret_cast<tag_t *>(
       MemToShadow(reinterpret_cast<uptr>(UntagPtr(tagged_ptr))));
-  return ptr_tag == mem_tag;
+  return PossiblyShortTagMatches(mem_tag, tagged_uptr, 1);
 }
 
 static void HwasanDeallocate(StackTrace *stack, void *tagged_ptr) {
   CHECK(tagged_ptr);
   HWASAN_FREE_HOOK(tagged_ptr);
 
   if (!PointerAndMemoryTagsMatch(tagged_ptr))
     ReportInvalidFree(stack, reinterpret_cast<uptr>(tagged_ptr));
 
   void *untagged_ptr = UntagPtr(tagged_ptr);
   void *aligned_ptr = reinterpret_cast<void *>(
       RoundDownTo(reinterpret_cast<uptr>(untagged_ptr), kShadowAlignment));
   Metadata *meta =
       reinterpret_cast<Metadata *>(allocator.GetMetaData(aligned_ptr));
   uptr orig_size = meta->requested_size;
   u32 free_context_id = StackDepotPut(*stack);
   u32 alloc_context_id = meta->alloc_context_id;
 
   // Check tail magic.
   uptr tagged_size = TaggedSize(orig_size);
-  if (flags()->free_checks_tail_magic && !right_align_mode && orig_size) {
-    uptr tail_size = tagged_size - orig_size;
+  if (flags()->free_checks_tail_magic && orig_size &&
+      tagged_size != orig_size) {
+    uptr tail_size = tagged_size - orig_size - 1;
     CHECK_LT(tail_size, kShadowAlignment);
     void *tail_beg = reinterpret_cast<void *>(
         reinterpret_cast<uptr>(aligned_ptr) + orig_size);
     if (tail_size && internal_memcmp(tail_beg, tail_magic, tail_size))
       ReportTailOverwritten(stack, reinterpret_cast<uptr>(tagged_ptr),
-                            orig_size, tail_size, tail_magic);
+                            orig_size, tail_magic);
   }
 
   meta->requested_size = 0;
   meta->alloc_context_id = 0;
   // This memory will not be reused by anyone else, so we are free to keep it
   // poisoned.
   Thread *t = GetCurrentThread();
   if (flags()->max_free_fill_size > 0) {

compiler-rt/lib/hwasan/hwasan_checks.h

asm volatile(
       "nopl %c0(%%rax)\n" ::"n"(0x40 + X),
       "D"(p), "S"(size));
 #else
   __builtin_trap();
 #endif
   // __builtin_unreachable();
 }
 
+__attribute__((always_inline, nodebug)) static bool PossiblyShortTagMatches(
+    tag_t mem_tag, uptr ptr, uptr sz) {
+  tag_t ptr_tag = GetTagFromPointer(ptr);
+  if (ptr_tag == mem_tag)
+    return true;
+  if (mem_tag > 15)
+    return false;
+  if ((ptr & 15) + sz > mem_tag)
+    return false;
+#ifndef __aarch64__
+  ptr = UntagAddr(ptr);
+#endif
+  return *(u8 *)(ptr | 15) == ptr_tag;
+}
+
 enum class ErrorAction { Abort, Recover };
 enum class AccessType { Load, Store };
 
 template <ErrorAction EA, AccessType AT, unsigned LogSize>
 __attribute__((always_inline, nodebug)) static void CheckAddress(uptr p) {
-  tag_t ptr_tag = GetTagFromPointer(p);
   uptr ptr_raw = p & ~kAddressTagMask;
   tag_t mem_tag = *(tag_t *)MemToShadow(ptr_raw);
-  if (UNLIKELY(ptr_tag != mem_tag)) {
+  if (UNLIKELY(!PossiblyShortTagMatches(mem_tag, p, 1 << LogSize))) {
     SigTrap<0x20 * (EA == ErrorAction::Recover) +
             0x10 * (AT == AccessType::Store) + LogSize>(p);
     if (EA == ErrorAction::Abort)
       __builtin_unreachable();
   }
 }
 
 template <ErrorAction EA, AccessType AT>
 __attribute__((always_inline, nodebug)) static void CheckAddressSized(uptr p,
                                                                       uptr sz) {
   if (sz == 0)
     return;
   tag_t ptr_tag = GetTagFromPointer(p);
   uptr ptr_raw = p & ~kAddressTagMask;
   tag_t *shadow_first = (tag_t *)MemToShadow(ptr_raw);
-  tag_t *shadow_last = (tag_t *)MemToShadow(ptr_raw + sz - 1);
-  for (tag_t *t = shadow_first; t <= shadow_last; ++t)
+  tag_t *shadow_last = (tag_t *)MemToShadow(ptr_raw + sz);
+  for (tag_t *t = shadow_first; t < shadow_last; ++t)
     if (UNLIKELY(ptr_tag != *t)) {
       SigTrap<0x20 * (EA == ErrorAction::Recover) +
               0x10 * (AT == AccessType::Store) + 0xf>(p, sz);
       if (EA == ErrorAction::Abort)
         __builtin_unreachable();
     }
+  uptr end = p + sz;
+  uptr tail_sz = end & 0xf;
+  if (UNLIKELY(tail_sz != 0 && !PossiblyShortTagMatches(
+                                   *shadow_last, end & ~0xfull, tail_sz))) {
+    SigTrap<0x20 * (EA == ErrorAction::Recover) +
+            0x10 * (AT == AccessType::Store) + 0xf>(p, sz);
+    if (EA == ErrorAction::Abort)
+      __builtin_unreachable();
+  }
 }
+
 }  // end namespace __hwasan
 
 #endif  // HWASAN_CHECKS_H

compiler-rt/lib/hwasan/hwasan_flags.inc

 // tags.
 HWASAN_FLAG(bool, random_tags, true, "")
 
 HWASAN_FLAG(
     int, max_malloc_fill_size, 0x1000,  // By default, fill only the first 4K.
     "HWASan allocator flag. max_malloc_fill_size is the maximal amount of "
     "bytes that will be filled with malloc_fill_byte on malloc.")
 
-// Rules for malloc alignment on aarch64:
-//   * If the size is 16-aligned, then malloc should return 16-aligned memory.
-//   * Otherwise, malloc should return 8-alignment memory.
-// So,
-//   * If the size is 16-aligned, we don't need to do anything.
-//   * Otherwise we don't have to obey 16-alignment, just the 8-alignment.
-//   * We may want to break the 8-alignment rule to catch more buffer overflows
-//     but this will break valid code in some rare cases, like this:
-//     struct Foo {
-//       // accessed via atomic instructions that require 8-alignment.
-//       std::atomic<int64_t> atomic_stuff;
-//       ...
-//       char vla[1];  // the actual size of vla could be anything.
-//     }
-// Which means that the safe values for malloc_align_right are 0, 8, 9,
-// and the values 1 and 2 may require changes in otherwise valid code.
-
-HWASAN_FLAG(
-    int, malloc_align_right, 0,  // off by default
-    "HWASan allocator flag. "
-    "0 (default): allocations are always aligned left to 16-byte boundary; "
-    "1: allocations are sometimes aligned right to 1-byte boundary (risky); "
-    "2: allocations are always aligned right to 1-byte boundary (risky); "
-    "8: allocations are sometimes aligned right to 8-byte boundary; "
-    "9: allocations are always aligned right to 8-byte boundary."
-  )
 HWASAN_FLAG(bool, free_checks_tail_magic, 1,
     "If set, free() will check the magic values "
     "to the right of the allocated object "
     "if the allocation size is not a divident of the granule size")
 HWASAN_FLAG(
     int, max_free_fill_size, 0,
     "HWASan allocator flag. max_free_fill_size is the maximal amount of "
     "bytes that will be filled with free_fill_byte during free.")

compiler-rt/lib/hwasan/hwasan_report.h

 
 namespace __hwasan {
 
 void ReportStats();
 void ReportTagMismatch(StackTrace *stack, uptr addr, uptr access_size,
                        bool is_store, bool fatal, uptr *registers_frame);
 void ReportInvalidFree(StackTrace *stack, uptr addr);
 void ReportTailOverwritten(StackTrace *stack, uptr addr, uptr orig_size,
-                           uptr tail_size, const u8 *expected);
+                           const u8 *expected);
 void ReportRegisters(uptr *registers_frame, uptr pc);
 void ReportAtExitStatistics();
 
 
 }  // namespace __hwasan
 
 #endif  // HWASAN_REPORT_H

compiler-rt/lib/hwasan/hwasan_report.cpp

if (SymbolizedStack *frame = Symbolizer::GetOrInit()->SymbolizePC(pc)) {
                   common_flags()->strip_path_prefix);
       frame->ClearAll();
     }
     Printf("%s", frame_desc.data());
     frame_desc.clear();
   }
 }
 
+// Returns true if tag == *tag_ptr, reading tags from short granules if
+// necessary. This may return a false positive if tags 1-15 are used as a
+// regular tag rather than a short granule marker.
+static bool TagsEqual(tag_t tag, tag_t *tag_ptr) {
+  if (tag == *tag_ptr)
+    return true;
+  if (*tag_ptr == 0 || *tag_ptr > kShadowAlignment - 1)
+    return false;
+  uptr mem = ShadowToMem(reinterpret_cast<uptr>(tag_ptr));
+  tag_t inline_tag = *reinterpret_cast<tag_t *>(mem + kShadowAlignment - 1);
+  return tag == inline_tag;
+}
+
 void PrintAddressDescription(
     uptr tagged_addr, uptr access_size,
     StackAllocationsRingBuffer *current_stack_allocations) {
   Decorator d;
   int num_descriptions_printed = 0;
   uptr untagged_addr = UntagAddr(tagged_addr);
 
   // Print some very basic information about the address, if it's a heap.
void PrintAddressDescription(
   }
 
   // Check if this looks like a heap buffer overflow by scanning
   // the shadow left and right and looking for the first adjacent
   // object with a different memory tag. If that tag matches addr_tag,
   // check the allocator if it has a live chunk there.
   tag_t addr_tag = GetTagFromPointer(tagged_addr);
   tag_t *tag_ptr = reinterpret_cast<tag_t*>(MemToShadow(untagged_addr));
-  if (*tag_ptr != addr_tag) { // should be true usually.
-    tag_t *left = tag_ptr, *right = tag_ptr;
-    // scan left.
-    for (int i = 0; i < 1000 && *left == *tag_ptr; i++, left--){}
-    // scan right.
-    for (int i = 0; i < 1000 && *right == *tag_ptr; i++, right++){}
-    // Chose the object that has addr_tag and that is closer to addr.
-    tag_t *candidate = nullptr;
-    if (*right == addr_tag && *left == addr_tag)
-      candidate = right - tag_ptr < tag_ptr - left ? right : left;
-    else if (*right == addr_tag)
-      candidate = right;
-    else if (*left == addr_tag)
+  tag_t *candidate = nullptr, *left = tag_ptr, *right = tag_ptr;
+  for (int i = 0; i < 1000; i++) {
+    if (TagsEqual(addr_tag, left)) {
       candidate = left;
+      break;
+    }
+    --left;
+    if (TagsEqual(addr_tag, right)) {
+      candidate = right;
+      break;
+    }
+    ++right;
+  }
 
-    if (candidate) {
-      uptr mem = ShadowToMem(reinterpret_cast<uptr>(candidate));
-      HwasanChunkView chunk = FindHeapChunkByAddress(mem);
-      if (chunk.IsAllocated()) {
-        Printf("%s", d.Location());
-        Printf(
-            "%p is located %zd bytes to the %s of %zd-byte region [%p,%p)\n",
+      Printf("%p is located %zd bytes to the %s of %zd-byte region [%p,%p)\n",
              untagged_addr,
              candidate == left ? untagged_addr - chunk.End()
                                : chunk.Beg() - untagged_addr,
-            candidate == right ? "left" : "right", chunk.UsedSize(),
+             candidate == left ? "right" : "left", chunk.UsedSize(),
              chunk.Beg(), chunk.End());
-        Printf("%s", d.Allocation());
-        Printf("allocated here:\n");
-        Printf("%s", d.Default());
-        GetStackTraceFromId(chunk.GetAllocStackId()).Print();
-        num_descriptions_printed++;
-      }
-    }
-  }
 
   hwasanThreadList().VisitAllLiveThreads([&](Thread *t) {
     // Scan all threads' ring buffers to find if it's a heap-use-after-free.
     HeapAllocationRecord har;
     if (uptr D = FindHeapAllocation(t->heap_allocations(), tagged_addr, &har)) {
       Printf("%s", d.Location());
       Printf("%p is located %zd bytes inside of %zd-byte region [%p,%p)\n",
              untagged_addr, untagged_addr - UntagAddr(har.tagged_addr),
void PrintAddressDescription(
 
   if (!num_descriptions_printed)
     // We exhausted our possibilities. Bail out.
     Printf("HWAddressSanitizer can not describe address in more detail.\n");
 }
 
 void ReportStats() {}
 
-static void PrintTagsAroundAddr(tag_t *tag_ptr) {
-  Printf(
-      "Memory tags around the buggy address (one tag corresponds to %zd "
-      "bytes):\n", kShadowAlignment);
-
+static void PrintTagInfoAroundAddr(tag_t *tag_ptr, uptr num_rows,
+                                   void (*print_tag)(InternalScopedString &s,
+                                                     tag_t *tag)) {
   const uptr row_len = 16;  // better be power of two.
-  const uptr num_rows = 17;
   tag_t *center_row_beg = reinterpret_cast<tag_t *>(
       RoundDownTo(reinterpret_cast<uptr>(tag_ptr), row_len));
   tag_t *beg_row = center_row_beg - row_len * (num_rows / 2);
   tag_t *end_row = center_row_beg + row_len * ((num_rows + 1) / 2);
   InternalScopedString s(GetPageSizeCached() * 8);
   for (tag_t *row = beg_row; row < end_row; row += row_len) {
     s.append("%s", row == center_row_beg ? "=>" : "  ");
     for (uptr i = 0; i < row_len; i++) {
       s.append("%s", row + i == tag_ptr ? "[" : " ");
-      s.append("%02x", row[i]);
+      print_tag(s, &row[i]);
       s.append("%s", row + i == tag_ptr ? "]" : " ");
     }
     s.append("%s\n", row == center_row_beg ? "<=" : "  ");
   }
   Printf("%s", s.data());
 }
 
+static void PrintTagsAroundAddr(tag_t *tag_ptr) {
+  Printf(
+      "Memory tags around the buggy address (one tag corresponds to %zd "
+      "bytes):\n", kShadowAlignment);
+  PrintTagInfoAroundAddr(tag_ptr, 17, [](InternalScopedString &s, tag_t *tag) {
+    s.append("%02x", *tag);
+  });
+
+  Printf(
+      "Tags for short granules around the buggy address (one tag corresponds "
+      "to %zd bytes):\n",
+      kShadowAlignment);
+  PrintTagInfoAroundAddr(tag_ptr, 3, [](InternalScopedString &s, tag_t *tag) {
+    if (*tag >= 1 && *tag <= kShadowAlignment) {
+      uptr granule_addr = ShadowToMem(reinterpret_cast<uptr>(tag));
+      s.append("%02x",
+               *reinterpret_cast<u8 *>(granule_addr + kShadowAlignment - 1));
+    } else {
+      s.append("..");
+    }
+  });
+  Printf(
+      "See "
+      "https://clang.llvm.org/docs/"
+      "HardwareAssistedAddressSanitizerDesign.html#short-granules for a "
+      "description of short granule tags\n");
+}
+
 void ReportInvalidFree(StackTrace *stack, uptr tagged_addr) {
   ScopedReport R(flags()->halt_on_error);
 
   uptr untagged_addr = UntagAddr(tagged_addr);
   tag_t ptr_tag = GetTagFromPointer(tagged_addr);
   tag_t *tag_ptr = reinterpret_cast<tag_t*>(MemToShadow(untagged_addr));
   tag_t mem_tag = *tag_ptr;
   Decorator d;
void ReportInvalidFree(StackTrace *stack, uptr tagged_addr) {
   PrintAddressDescription(tagged_addr, 0, nullptr);
 
   PrintTagsAroundAddr(tag_ptr);
 
   ReportErrorSummary(bug_type, stack);
 }
 
 void ReportTailOverwritten(StackTrace *stack, uptr tagged_addr, uptr orig_size,
-                           uptr tail_size, const u8 *expected) {
+                           const u8 *expected) {
+  uptr tail_size = kShadowAlignment - (orig_size % kShadowAlignment);
   ScopedReport R(flags()->halt_on_error);
   Decorator d;
   uptr untagged_addr = UntagAddr(tagged_addr);
   Printf("%s", d.Error());
   const char *bug_type = "alocation-tail-overwritten";
   Report("ERROR: %s: %s; heap object [%p,%p) of size %zd\n", SanitizerToolName,
          bug_type, untagged_addr, untagged_addr + orig_size, orig_size);
   Printf("\n%s", d.Default());
for (uptr i = 0; i < kShadowAlignment - tail_size; i++)
     s.append("   ");
   for (uptr i = 0; i < tail_size; i++)
     s.append("%s ", expected[i] != tail[i] ? "^^" : "  ");
 
   s.append("\nThis error occurs when a buffer overflow overwrites memory\n"
     "to the right of a heap object, but within the %zd-byte granule, e.g.\n"
     "   char *x = new char[20];\n"
     "   x[25] = 42;\n"
-    "By default %s does not detect such bugs at the time of write,\n"
-    "but can detect them at the time of free/delete.\n"
-    "To disable this feature set HWASAN_OPTIONS=free_checks_tail_magic=0;\n"
-    "To enable checking at the time of access, set "
-    "HWASAN_OPTIONS=malloc_align_right to non-zero\n\n",
+    "%s does not detect such bugs in uninstrumented code at the time of write,"
+    "\nbut can detect them at the time of free/delete.\n"
+    "To disable this feature set HWASAN_OPTIONS=free_checks_tail_magic=0\n",
     kShadowAlignment, SanitizerToolName);
   Printf("%s", s.data());
   GetCurrentThread()->Announce();
 
   tag_t *tag_ptr = reinterpret_cast<tag_t*>(MemToShadow(untagged_addr));
   PrintTagsAroundAddr(tag_ptr);
 
   ReportErrorSummary(bug_type, stack);

compiler-rt/test/hwasan/TestCases/heap-buffer-overflow.c

 // RUN: %clang_hwasan  %s -o %t
-// RUN:                                       not %run %t 40 2>&1 | FileCheck %s --check-prefix=CHECK40-LEFT
-// RUN: %env_hwasan_opts=malloc_align_right=2 not %run %t 40 2>&1 | FileCheck %s --check-prefix=CHECK40-RIGHT
-// RUN:                                       not %run %t 80 2>&1 | FileCheck %s --check-prefix=CHECK80-LEFT
-// RUN: %env_hwasan_opts=malloc_align_right=2 not %run %t 80 2>&1 | FileCheck %s --check-prefix=CHECK80-RIGHT
+// RUN: not %run %t 40 2>&1 | FileCheck %s --check-prefix=CHECK40
+// RUN: not %run %t 80 2>&1 | FileCheck %s --check-prefix=CHECK80
 // RUN: not %run %t -30 2>&1 | FileCheck %s --check-prefix=CHECKm30
 // RUN: not %run %t -30 1000000 2>&1 | FileCheck %s --check-prefix=CHECKMm30
 // RUN: not %run %t 1000000 1000000 2>&1 | FileCheck %s --check-prefix=CHECKM
 
 // Test OOB within the granule.
-// Misses the bug when malloc is left-aligned, catches it otherwise.
-// RUN:                                           %run %t 31
-// RUN: %env_hwasan_opts=malloc_align_right=2 not %run %t 31 2>&1 | FileCheck %s --check-prefix=CHECK31
-
-// RUN:                                           %run %t 30 20
-// RUN: %env_hwasan_opts=malloc_align_right=9 not %run %t 30 20 2>&1 | FileCheck %s --check-prefix=CHECK20-RIGHT8
-
-// RUN: %env_hwasan_opts=malloc_align_right=42 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-WRONG-FLAG
+// RUN: not %run %t 31 2>&1 | FileCheck %s --check-prefix=CHECK31
+// RUN: not %run %t 30 20 2>&1 | FileCheck %s --check-prefix=CHECK20
 
 // REQUIRES: stable-runtime
 
 #include <stdlib.h>
 #include <stdio.h>
 #include <sanitizer/hwasan_interface.h>
 
 static volatile char sink;
 
 int main(int argc, char **argv) {
   __hwasan_enable_allocator_tagging();
   int offset = argc < 2 ? 40 : atoi(argv[1]);
   int size = argc < 3 ? 30 : atoi(argv[2]);
   char * volatile x = (char*)malloc(size);
   fprintf(stderr, "base: %p access: %p\n", x, &x[offset]);
   sink = x[offset];
 
-// CHECK40-LEFT: allocated heap chunk; size: 32 offset: 8
-// CHECK40-LEFT: is located 10 bytes to the right of 30-byte region
-// CHECK40-RIGHT: allocated heap chunk; size: 32 offset:
-// CHECK40-RIGHT: is located 10 bytes to the right of 30-byte region
-//
-// CHECK80-LEFT: allocated heap chunk; size: 32 offset: 16
-// CHECK80-LEFT: is located 50 bytes to the right of 30-byte region
-// CHECK80-RIGHT: allocated heap chunk; size: 32 offset:
-// CHECK80-RIGHT: is located 50 bytes to the right of 30-byte region
+// CHECK40: allocated heap chunk; size: 32 offset: 8
+// CHECK40: is located 10 bytes to the right of 30-byte region
+//
+// CHECK80: allocated heap chunk; size: 32 offset: 16
+// CHECK80: is located 50 bytes to the right of 30-byte region
 //
 // CHECKm30: is located 30 bytes to the left of 30-byte region
 //
 // CHECKMm30: is a large allocated heap chunk; size: 1003520 offset: -30
 // CHECKMm30: is located 30 bytes to the left of 1000000-byte region
 //
 // CHECKM: is a large allocated heap chunk; size: 1003520 offset: 1000000
 // CHECKM: is located 0 bytes to the right of 1000000-byte region
 //
+// CHECK31: tags: [[TAG:..]]/0e (ptr/mem)
 // CHECK31: is located 1 bytes to the right of 30-byte region
+// CHECK31: Memory tags around the buggy address
+// CHECK31: [0e]
+// CHECK31: Tags for short granules around the buggy address
+// CHECK31: {{\[}}[[TAG]]]
 //
-// CHECK20-RIGHT8: is located 10 bytes to the right of 20-byte region [0x{{.*}}8,0x{{.*}}c)
-//
-// CHECK-WRONG-FLAG: ERROR: unsupported value of malloc_align_right flag: 42
+// CHECK20: is located 10 bytes to the right of 20-byte region [0x{{.*}}0,0x{{.*}}4)
   free(x);
 }

compiler-rt/test/hwasan/TestCases/random-align-right.c

-// Tests malloc_align_right=1 and 8 (randomly aligning right).
-// RUN: %clang_hwasan  %s -o %t
-//
-// RUN: %run %t 20
-// RUN: %run %t 30
-// RUN: %env_hwasan_opts=malloc_align_right=1 not %run %t 20 2>&1 | FileCheck %s --check-prefix=CHECK20
-// RUN: %env_hwasan_opts=malloc_align_right=1 not %run %t 30 2>&1 | FileCheck %s --check-prefix=CHECK30
-// RUN: %env_hwasan_opts=malloc_align_right=8 not %run %t 30 2>&1 | FileCheck %s --check-prefix=CHECK30
-
-// REQUIRES: stable-runtime
-
-#include <stdlib.h>
-#include <stdio.h>
-#include <sanitizer/hwasan_interface.h>
-
-static volatile void *sink;
-
-int main(int argc, char **argv) {
-  __hwasan_enable_allocator_tagging();
-  int index = atoi(argv[1]);
-
-  // Perform 1000 buffer overflows within the 16-byte granule,
-  // so that random right-alignment has a very high chance of
-  // catching at least one of them.
-  for (int i = 0; i < 1000; i++) {
-    char *p = (char*)malloc(20);
-    sink = p;
-    p[index] = 0;
-// index=20 requires malloc_align_right=1 to catch
-// CHECK20: HWAddressSanitizer: tag-mismatch
-// index=30 requires malloc_align_right={1,8} to catch
-// CHECK30: HWAddressSanitizer: tag-mismatch
-  }
-}
-

compiler-rt/test/hwasan/TestCases/stack-oob.c

+// RUN: %clang_hwasan -DSIZE=15 -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
 // RUN: %clang_hwasan -DSIZE=16 -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
 // RUN: %clang_hwasan -DSIZE=64 -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
 // RUN: %clang_hwasan -DSIZE=0x1000 -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 // REQUIRES: stable-runtime
 
 #include <stdlib.h>
 #include <sanitizer/hwasan_interface.h>
 
 __attribute__((noinline))
 int f() {
   char z[SIZE];
   char *volatile p = z;
   return p[SIZE];
 }
 
 int main() {
   return f();
   // CHECK: READ of size 1 at
-  // CHECK: #0 {{.*}} in f{{.*}}stack-oob.c:14
+  // CHECK: #0 {{.*}} in f{{.*}}stack-oob.c:15
 
   // CHECK: is located in stack of threa
 
   // CHECK: SUMMARY: HWAddressSanitizer: tag-mismatch {{.*}} in f
 }

compiler-rt/test/hwasan/TestCases/tail-magic.c

 // Tests free_checks_tail_magic=1.
 // RUN: %clang_hwasan  %s -o %t
 // RUN: %env_hwasan_opts=free_checks_tail_magic=0     %run %t
 // RUN: %env_hwasan_opts=free_checks_tail_magic=1 not %run %t 2>&1 | FileCheck %s
 // RUN:                                           not %run %t 2>&1 | FileCheck %s
 
 // REQUIRES: stable-runtime
 
 #include <stdlib.h>
 #include <stdio.h>
 #include <sanitizer/hwasan_interface.h>
 
-static volatile void *sink;
+static volatile char *sink;
+
+// Overwrite the tail in a non-hwasan function so that we don't detect the
+// stores as OOB.
+__attribute__((no_sanitize("hwaddress"))) void overwrite_tail() {
+  sink[20] = 0x42;
+  sink[24] = 0x66;
+}
 
 int main(int argc, char **argv) {
   __hwasan_enable_allocator_tagging();
 
   char *p = (char*)malloc(20);
-  sink = p;
-  p[20] = 0x42;
-  p[24] = 0x66;
+  sink = (char *)((uintptr_t)(p) & 0xffffffffffffff);
+  overwrite_tail();
   free(p);
 // CHECK: ERROR: HWAddressSanitizer: alocation-tail-overwritten; heap object [{{.*}}) of size 20
 // CHECK: in main {{.*}}tail-magic.c:[[@LINE-2]]
 // CHECK: allocated here:
-// CHECK: in main {{.*}}tail-magic.c:[[@LINE-8]]
+// CHECK: in main {{.*}}tail-magic.c:[[@LINE-7]]
 // CHECK: Tail contains: .. .. .. .. 42 {{.. .. ..}} 66
 }

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

OutStreamer->EmitInstruction(MCInstBuilder(AArch64::LDRBBroX)
                                  *STI);
     OutStreamer->EmitInstruction(
         MCInstBuilder(AArch64::SUBSXrs)
             .addReg(AArch64::XZR)
             .addReg(AArch64::X16)
             .addReg(Reg)
             .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSR, 56)),
         *STI);
-    MCSymbol *HandleMismatchSym = OutContext.createTempSymbol();
+    MCSymbol *HandlePartialSym = OutContext.createTempSymbol();
     OutStreamer->EmitInstruction(
         MCInstBuilder(AArch64::Bcc)
             .addImm(AArch64CC::NE)
-            .addExpr(MCSymbolRefExpr::create(HandleMismatchSym, OutContext)),
+            .addExpr(MCSymbolRefExpr::create(HandlePartialSym, OutContext)),
         *STI);
+    MCSymbol *ReturnSym = OutContext.createTempSymbol();
+    OutStreamer->EmitLabel(ReturnSym);
     OutStreamer->EmitInstruction(
         MCInstBuilder(AArch64::RET).addReg(AArch64::LR), *STI);
 
-    OutStreamer->EmitLabel(HandleMismatchSym);
+    OutStreamer->EmitLabel(HandlePartialSym);
+    OutStreamer->EmitInstruction(MCInstBuilder(AArch64::SUBSWri)
+                                     .addReg(AArch64::WZR)
+                                     .addReg(AArch64::W16)
+                                     .addImm(15)
+                                     .addImm(0),
+                                 *STI);
+    MCSymbol *HandleMismatchSym = OutContext.createTempSymbol();
+    OutStreamer->EmitInstruction(
+        MCInstBuilder(AArch64::Bcc)
+            .addImm(AArch64CC::HI)
+            .addExpr(MCSymbolRefExpr::create(HandleMismatchSym, OutContext)),
+        *STI);
+
+    OutStreamer->EmitInstruction(
+        MCInstBuilder(AArch64::ANDXri)
+            .addReg(AArch64::X17)
+            .addReg(Reg)
+            .addImm(AArch64_AM::encodeLogicalImmediate(0xf, 64)),
+        *STI);
+    size_t Size = 1 << (AccessInfo & 0xf);
+    if (Size != 1)
+      OutStreamer->EmitInstruction(MCInstBuilder(AArch64::ADDXri)
+                                       .addReg(AArch64::X17)
+                                       .addReg(AArch64::X17)
+                                       .addImm(Size - 1)
+                                       .addImm(0),
+                                   *STI);
+    OutStreamer->EmitInstruction(MCInstBuilder(AArch64::SUBSWrs)
+                                     .addReg(AArch64::WZR)
+                                     .addReg(AArch64::W16)
+                                     .addReg(AArch64::W17)
+                                     .addImm(0),
+                                 *STI);
+    OutStreamer->EmitInstruction(
+        MCInstBuilder(AArch64::Bcc)
+            .addImm(AArch64CC::LS)
+            .addExpr(MCSymbolRefExpr::create(HandleMismatchSym, OutContext)),
+        *STI);
+
+    OutStreamer->EmitInstruction(
+        MCInstBuilder(AArch64::ORRXri)
+            .addReg(AArch64::X16)
+            .addReg(Reg)
+            .addImm(AArch64_AM::encodeLogicalImmediate(0xf, 64)),
+        *STI);
+    OutStreamer->EmitInstruction(MCInstBuilder(AArch64::LDRBBui)
+                                     .addReg(AArch64::W16)
+                                     .addReg(AArch64::X16)
+                                     .addImm(0),
+                                 *STI);
+    OutStreamer->EmitInstruction(
+        MCInstBuilder(AArch64::SUBSXrs)
+            .addReg(AArch64::XZR)
+            .addReg(AArch64::X16)
+            .addReg(Reg)
+            .addImm(AArch64_AM::getShifterImm(AArch64_AM::LSR, 56)),
+        *STI);
+    OutStreamer->EmitInstruction(
+        MCInstBuilder(AArch64::Bcc)
+            .addImm(AArch64CC::EQ)
+            .addExpr(MCSymbolRefExpr::create(ReturnSym, OutContext)),
+        *STI);
 
+    OutStreamer->EmitLabel(HandleMismatchSym);
     OutStreamer->EmitInstruction(MCInstBuilder(AArch64::STPXpre)
                                      .addReg(AArch64::SP)
                                      .addReg(AArch64::X0)
                                      .addReg(AArch64::X1)
                                      .addReg(AArch64::SP)
                                      .addImm(-32),
                                  *STI);
     OutStreamer->EmitInstruction(MCInstBuilder(AArch64::STPXi)

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

void instrumentMemAccessInline(Value *Ptr, bool IsWrite,
                                  Instruction *InsertBefore);
   void instrumentMemIntrinsic(MemIntrinsic *MI);
   bool instrumentMemAccess(Instruction *I);
   Value *isInterestingMemoryAccess(Instruction *I, bool *IsWrite,
                                    uint64_t *TypeSize, unsigned *Alignment,
                                    Value **MaybeMask);
 
   bool isInterestingAlloca(const AllocaInst &AI);
-  bool tagAlloca(IRBuilder<> &IRB, AllocaInst *AI, Value *Tag);
+  bool tagAlloca(IRBuilder<> &IRB, AllocaInst *AI, Value *Tag, bool Zero);
   Value *tagPointer(IRBuilder<> &IRB, Type *Ty, Value *PtrLong, Value *Tag);
   Value *untagPointer(IRBuilder<> &IRB, Value *PtrLong);
   bool instrumentStack(
       SmallVectorImpl<AllocaInst *> &Allocas,
       DenseMap<AllocaInst *, std::vector<DbgDeclareInst *>> &AllocaDeclareMap,
       SmallVectorImpl<Instruction *> &RetVec, Value *StackTag);
   Value *readRegister(IRBuilder<> &IRB, StringRef Name);
   bool instrumentLandingPads(SmallVectorImpl<Instruction *> &RetVec);
int matchAllTag = ClMatchAllTag.getNumOccurrences() > 0 ?
       ClMatchAllTag : (CompileKernel ? 0xFF : -1);
   if (matchAllTag != -1) {
     Value *TagNotIgnored = IRB.CreateICmpNE(PtrTag,
         ConstantInt::get(PtrTag->getType(), matchAllTag));
     TagMismatch = IRB.CreateAnd(TagMismatch, TagNotIgnored);
   }
 
   Instruction *CheckTerm =
-      SplitBlockAndInsertIfThen(TagMismatch, InsertBefore, !Recover,
+      SplitBlockAndInsertIfThen(TagMismatch, InsertBefore, false,
                                 MDBuilder(*C).createBranchWeights(1, 100000));
 
   IRB.SetInsertPoint(CheckTerm);
+  Value *OutOfShortGranuleTagRange =
+      IRB.CreateICmpUGT(MemTag, ConstantInt::get(Int8Ty, 15));
+  Instruction *CheckFailTerm =
+      SplitBlockAndInsertIfThen(OutOfShortGranuleTagRange, CheckTerm, !Recover,
+                                MDBuilder(*C).createBranchWeights(1, 100000));
+
+  IRB.SetInsertPoint(CheckTerm);
+  Value *PtrLowBits = IRB.CreateTrunc(IRB.CreateAnd(PtrLong, 15), Int8Ty);
+  PtrLowBits = IRB.CreateAdd(
+      PtrLowBits, ConstantInt::get(Int8Ty, (1 << AccessSizeIndex) - 1));
+  Value *PtrLowBitsOOB = IRB.CreateICmpUGE(PtrLowBits, MemTag);
+  SplitBlockAndInsertIfThen(PtrLowBitsOOB, CheckTerm, false,
+                            MDBuilder(*C).createBranchWeights(1, 100000),
+                            nullptr, nullptr, CheckFailTerm->getParent());
+
+  IRB.SetInsertPoint(CheckTerm);
+  Value *InlineTagAddr = IRB.CreateOr(AddrLong, 15);
+  InlineTagAddr = IRB.CreateIntToPtr(InlineTagAddr, Int8PtrTy);
+  Value *InlineTag = IRB.CreateLoad(Int8Ty, InlineTagAddr);
+  Value *InlineTagMismatch = IRB.CreateICmpNE(PtrTag, InlineTag);
+  SplitBlockAndInsertIfThen(InlineTagMismatch, CheckTerm, false,
+                            MDBuilder(*C).createBranchWeights(1, 100000),
+                            nullptr, nullptr, CheckFailTerm->getParent());
+
+  IRB.SetInsertPoint(CheckFailTerm);
   InlineAsm *Asm;
   switch (TargetTriple.getArch()) {
     case Triple::x86_64:
       // The signal handler will find the data address in rdi.
       Asm = InlineAsm::get(
           FunctionType::get(IRB.getVoidTy(), {PtrLong->getType()}, false),
           "int3\nnopl " + itostr(0x40 + AccessInfo) + "(%rax)",
           "{rdi}",
           /*hasSideEffects=*/true);
       break;
     case Triple::aarch64:
     case Triple::aarch64_be:
       // The signal handler will find the data address in x0.
       Asm = InlineAsm::get(
           FunctionType::get(IRB.getVoidTy(), {PtrLong->getType()}, false),
           "brk #" + itostr(0x900 + AccessInfo),
           "{x0}",
           /*hasSideEffects=*/true);
       break;
     default:
       report_fatal_error("unsupported architecture");
   }
   IRB.CreateCall(Asm, PtrLong);
+  if (Recover)
+    cast<BranchInst>(CheckFailTerm)->setSuccessor(0, CheckTerm->getParent());
 }
 
 void HWAddressSanitizer::instrumentMemIntrinsic(MemIntrinsic *MI) {
   IRBuilder<> IRB(MI);
   if (isa<MemTransferInst>(MI)) {
     IRB.CreateCall(
         isa<MemMoveInst>(MI) ? HWAsanMemmove : HWAsanMemcpy,
         {IRB.CreatePointerCast(MI->getOperand(0), IRB.getInt8PtrTy()),
if (AI.isArrayAllocation()) {
     ArraySize = CI->getZExtValue();
   }
   Type *Ty = AI.getAllocatedType();
   uint64_t SizeInBytes = AI.getModule()->getDataLayout().getTypeAllocSize(Ty);
   return SizeInBytes * ArraySize;
 }
 
 bool HWAddressSanitizer::tagAlloca(IRBuilder<> &IRB, AllocaInst *AI,
-                                   Value *Tag) {
-  size_t Size = (getAllocaSizeInBytes(*AI) + Mapping.getAllocaAlignment() - 1) &
-                ~(Mapping.getAllocaAlignment() - 1);
+                                   Value *Tag, bool Zero) {
+  size_t Size = getAllocaSizeInBytes(*AI);
+  size_t AlignedSize = alignTo(Size, Mapping.getAllocaAlignment());
+  if (Zero)
+    Size = AlignedSize;
 
   Value *JustTag = IRB.CreateTrunc(Tag, IRB.getInt8Ty());
   if (ClInstrumentWithCalls) {
     IRB.CreateCall(HwasanTagMemoryFunc,
                    {IRB.CreatePointerCast(AI, Int8PtrTy), JustTag,
-                    ConstantInt::get(IntptrTy, Size)});
+                    ConstantInt::get(IntptrTy, AlignedSize)});
   } else {
     size_t ShadowSize = Size >> Mapping.Scale;
     Value *ShadowPtr = memToShadow(IRB.CreatePointerCast(AI, IntptrTy), IRB);
     // If this memset is not inlined, it will be intercepted in the hwasan
     // runtime library. That's OK, because the interceptor skips the checks if
     // the address is in the shadow region.
     // FIXME: the interceptor is not as fast as real memset. Consider lowering
     // llvm.memset right here into either a sequence of stores, or a call to
     // hwasan_tag_memory.
+    if (ShadowSize)
       IRB.CreateMemSet(ShadowPtr, JustTag, ShadowSize, /*Align=*/1);
+    if (Size != AlignedSize) {
+      IRB.CreateStore(
+          ConstantInt::get(Int8Ty, Size % Mapping.getAllocaAlignment()),
+          IRB.CreateConstGEP1_32(Int8Ty, ShadowPtr, ShadowSize));
+      IRB.CreateStore(JustTag, IRB.CreateConstGEP1_32(
+                                   Int8Ty, IRB.CreateBitCast(AI, Int8PtrTy),
+                                   AlignedSize - 1));
+    }
   }
   return true;
 }
 
 static unsigned RetagMask(unsigned AllocaNo) {
   // A list of 8-bit numbers that have at most one run of non-zero bits.
   // x = x ^ (mask << 56) can be encoded as a single armv8 instruction for these
   // masks.
for (unsigned N = 0; N < Allocas.size(); ++N) {
 
     for (auto *DDI : AllocaDeclareMap.lookup(AI)) {
       DIExpression *OldExpr = DDI->getExpression();
       DIExpression *NewExpr = DIExpression::append(
           OldExpr, {dwarf::DW_OP_LLVM_tag_offset, RetagMask(N)});
       DDI->setArgOperand(2, MetadataAsValue::get(*C, NewExpr));
     }
 
-    tagAlloca(IRB, AI, Tag);
+    tagAlloca(IRB, AI, Tag, false);
 
     for (auto RI : RetVec) {
       IRB.SetInsertPoint(RI);
 
       // Re-tag alloca memory with the special UAR tag.
       Value *Tag = getUARTag(IRB, StackTag);
-      tagAlloca(IRB, AI, Tag);
+      tagAlloca(IRB, AI, Tag, true);
     }
   }
 
   return true;
 }
 
 bool HWAddressSanitizer::isInterestingAlloca(const AllocaInst &AI) {
   return (AI.getAllocatedType()->isSized() &&
bool HWAddressSanitizer::sanitizeFunction(Function &F) {
   SmallVector<AllocaInst*, 8> AllocasToInstrument;
   SmallVector<Instruction*, 8> RetVec;
   SmallVector<Instruction*, 8> LandingPadVec;
   DenseMap<AllocaInst *, std::vector<DbgDeclareInst *>> AllocaDeclareMap;
   for (auto &BB : F) {
     for (auto &Inst : BB) {
       if (ClInstrumentStack)
         if (AllocaInst *AI = dyn_cast<AllocaInst>(&Inst)) {
-          // Realign all allocas. We don't want small uninteresting allocas to
-          // hide in instrumented alloca's padding.
-          if (AI->getAlignment() < Mapping.getAllocaAlignment())
-            AI->setAlignment(Mapping.getAllocaAlignment());
-          // Instrument some of them.
           if (isInterestingAlloca(*AI))
             AllocasToInstrument.push_back(AI);
           continue;
         }
 
       if (isa<ReturnInst>(Inst) || isa<ResumeInst>(Inst) ||
           isa<CleanupReturnInst>(Inst))
         RetVec.push_back(&Inst);
bool HWAddressSanitizer::sanitizeFunction(Function &F) {
   bool Changed = false;
   if (!AllocasToInstrument.empty()) {
     Value *StackTag =
         ClGenerateTagsWithCalls ? nullptr : getStackBaseTag(EntryIRB);
     Changed |= instrumentStack(AllocasToInstrument, AllocaDeclareMap, RetVec,
                                StackTag);
   }
 
+  // Pad and align each of the allocas that we instrumented to stop small
+  // uninteresting allocas from hiding in instrumented alloca's padding and so
+  // that we have enough space to store real tags for short granules.
+  DenseMap<AllocaInst *, AllocaInst *> AllocaToPaddedAllocaMap;
+  for (AllocaInst *AI : AllocasToInstrument) {
+    uint64_t Size = getAllocaSizeInBytes(*AI);
+    uint64_t AlignedSize = alignTo(Size, Mapping.getAllocaAlignment());
+    AI->setAlignment(std::max(AI->getAlignment(), 16u));
+    if (Size != AlignedSize) {
+      Type *TypeWithPadding = StructType::get(
+          AI->getAllocatedType(), ArrayType::get(Int8Ty, AlignedSize - Size));
+      auto *NewAI = new AllocaInst(
+          TypeWithPadding, AI->getType()->getAddressSpace(), nullptr, "", AI);
+      NewAI->takeName(AI);
+      NewAI->setAlignment(AI->getAlignment());
+      NewAI->setUsedWithInAlloca(AI->isUsedWithInAlloca());
+      NewAI->setSwiftError(AI->isSwiftError());
+      NewAI->copyMetadata(*AI);
+      Value *Zero = ConstantInt::get(Int32Ty, 0);
+      auto *GEP = GetElementPtrInst::Create(TypeWithPadding, NewAI,
+                                            {Zero, Zero}, "", AI);
+      AI->replaceAllUsesWith(GEP);
+      AllocaToPaddedAllocaMap[AI] = NewAI;
+    }
+  }
+
+  if (!AllocaToPaddedAllocaMap.empty()) {
+    for (auto &BB : F)
+      for (auto &Inst : BB)
+        if (auto *DVI = dyn_cast<DbgVariableIntrinsic>(&Inst))
+          if (auto *AI =
+                  dyn_cast_or_null<AllocaInst>(DVI->getVariableLocation()))
+            if (auto *NewAI = AllocaToPaddedAllocaMap.lookup(AI))
+              DVI->setArgOperand(
+                  0, MetadataAsValue::get(*C, LocalAsMetadata::get(NewAI)));
+    for (auto &P : AllocaToPaddedAllocaMap)
+      P.first->eraseFromParent();
+  }
+
   // If we split the entry block, move any allocas that were originally in the
   // entry block back into the entry block so that they aren't treated as
   // dynamic allocas.
   if (EntryIRB.GetInsertBlock() != &F.getEntryBlock()) {
     InsertPt = &*F.getEntryBlock().begin();
     for (auto II = EntryIRB.GetInsertBlock()->begin(),
               IE = EntryIRB.GetInsertBlock()->end();
          II != IE;) {

llvm/test/CodeGen/AArch64/hwasan-check-memaccess.ll

 ; CHECK-NEXT: .type __hwasan_check_x0_456,@function
 ; CHECK-NEXT: .weak __hwasan_check_x0_456
 ; CHECK-NEXT: .hidden __hwasan_check_x0_456
 ; CHECK-NEXT: __hwasan_check_x0_456:
 ; CHECK-NEXT: ubfx x16, x0, #4, #52
 ; CHECK-NEXT: ldrb w16, [x9, x16]
 ; CHECK-NEXT: cmp x16, x0, lsr #56
 ; CHECK-NEXT: b.ne .Ltmp0
+; CHECK-NEXT: .Ltmp1:
 ; CHECK-NEXT: ret
 ; CHECK-NEXT: .Ltmp0:
+; CHECK-NEXT: cmp w16, #15
+; CHECK-NEXT: b.hi .Ltmp2
+; CHECK-NEXT: and x17, x0, #0xf
+; CHECK-NEXT: add x17, x17, #255
+; CHECK-NEXT: cmp w16, w17
+; CHECK-NEXT: b.ls .Ltmp2
+; CHECK-NEXT: orr x16, x0, #0xf
+; CHECK-NEXT: ldrb w16, [x16]
+; CHECK-NEXT: cmp x16, x0, lsr #56
+; CHECK-NEXT: b.eq .Ltmp1
+; CHECK-NEXT: .Ltmp2:
 ; CHECK-NEXT: stp x0, x1, [sp, #-256]!
 ; CHECK-NEXT: stp x29, x30, [sp, #232]
 ; CHECK-NEXT: mov x1, #456
 ; CHECK-NEXT: adrp  x16, :got:__hwasan_tag_mismatch
 ; CHECK-NEXT: ldr x16, [x16, :got_lo12:__hwasan_tag_mismatch]
 ; CHECK-NEXT: br  x16
 
 
 ; CHECK:      .section .text.hot,"axG",@progbits,__hwasan_check_x1_123,comdat
 ; CHECK-NEXT: .type __hwasan_check_x1_123,@function
 ; CHECK-NEXT: .weak __hwasan_check_x1_123
 ; CHECK-NEXT: .hidden __hwasan_check_x1_123
 ; CHECK-NEXT: __hwasan_check_x1_123:
 ; CHECK-NEXT: ubfx x16, x1, #4, #52
 ; CHECK-NEXT: ldrb w16, [x9, x16]
 ; CHECK-NEXT: cmp x16, x1, lsr #56
-; CHECK-NEXT: b.ne .Ltmp1
+; CHECK-NEXT: b.ne .Ltmp3
+; CHECK-NEXT: .Ltmp4:
 ; CHECK-NEXT: ret
-; CHECK-NEXT: .Ltmp1:
+; CHECK-NEXT: .Ltmp3:
+; CHECK-NEXT: cmp w16, #15
+; CHECK-NEXT: b.hi .Ltmp5
+; CHECK-NEXT: and x17, x1, #0xf
+; CHECK-NEXT: add x17, x17, #2047
+; CHECK-NEXT: cmp w16, w17
+; CHECK-NEXT: b.ls .Ltmp5
+; CHECK-NEXT: orr x16, x1, #0xf
+; CHECK-NEXT: ldrb w16, [x16]
+; CHECK-NEXT: cmp x16, x1, lsr #56
+; CHECK-NEXT: b.eq .Ltmp4
+; CHECK-NEXT: .Ltmp5:
 ; CHECK-NEXT: stp x0, x1, [sp, #-256]!
 ; CHECK-NEXT: stp x29, x30, [sp, #232]
 ; CHECK-NEXT: mov x0, x1
 ; CHECK-NEXT: mov x1, #123
 ; CHECK-NEXT: adrp  x16, :got:__hwasan_tag_mismatch
 ; CHECK-NEXT: ldr x16, [x16, :got_lo12:__hwasan_tag_mismatch]
 ; CHECK-NEXT: br  x16

llvm/test/Instrumentation/HWAddressSanitizer/alloca-with-calls.ll

 ; Test alloca instrumentation when tags are generated by HWASan function.
 ;
 ; RUN: opt < %s -hwasan -hwasan-generate-tags-with-calls -S | FileCheck %s
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 target triple = "aarch64--linux-android"
 
 declare void @use32(i32*)
 
 define void @test_alloca() sanitize_hwaddress {
 ; CHECK-LABEL: @test_alloca(
+; CHECK: %[[GEP:[^ ]*]] = getelementptr { i32, [12 x i8] }, { i32, [12 x i8] }* %x, i32 0, i32 0
 ; CHECK: %[[T1:[^ ]*]] = call i8 @__hwasan_generate_tag()
 ; CHECK: %[[A:[^ ]*]] = zext i8 %[[T1]] to i64
-; CHECK: %[[B:[^ ]*]] = ptrtoint i32* %x to i64
+; CHECK: %[[B:[^ ]*]] = ptrtoint i32* %[[GEP]] to i64
 ; CHECK: %[[C:[^ ]*]] = shl i64 %[[A]], 56
 ; CHECK: or i64 %[[B]], %[[C]]
 
 entry:
   %x = alloca i32, align 4
   call void @use32(i32* nonnull %x)
   ret void
 }

llvm/test/Instrumentation/HWAddressSanitizer/alloca.ll

 
 define void @test_alloca() sanitize_hwaddress {
 ; CHECK-LABEL: @test_alloca(
 ; CHECK: %[[FP:[^ ]*]] = call i8* @llvm.frameaddress(i32 0)
 ; CHECK: %[[A:[^ ]*]] = ptrtoint i8* %[[FP]] to i64
 ; CHECK: %[[B:[^ ]*]] = lshr i64 %[[A]], 20
 ; CHECK: %[[BASE_TAG:[^ ]*]] = xor i64 %[[A]], %[[B]]
 
-; CHECK: %[[X:[^ ]*]] = alloca i32, align 16
+; CHECK: %[[X:[^ ]*]] = alloca { i32, [12 x i8] }, align 16
+; CHECK: %[[X_GEP:[^ ]*]] = getelementptr { i32, [12 x i8] }, { i32, [12 x i8] }* %[[X]], i32 0, i32 0
 ; CHECK: %[[X_TAG:[^ ]*]] = xor i64 %[[BASE_TAG]], 0
-; CHECK: %[[X1:[^ ]*]] = ptrtoint i32* %[[X]] to i64
+; CHECK: %[[X1:[^ ]*]] = ptrtoint i32* %[[X_GEP]] to i64
 ; CHECK: %[[C:[^ ]*]] = shl i64 %[[X_TAG]], 56
 ; CHECK: %[[D:[^ ]*]] = or i64 %[[X1]], %[[C]]
 ; CHECK: %[[X_HWASAN:[^ ]*]] = inttoptr i64 %[[D]] to i32*
 
 ; CHECK: %[[X_TAG2:[^ ]*]] = trunc i64 %[[X_TAG]] to i8
-; CHECK: %[[E:[^ ]*]] = ptrtoint i32* %[[X]] to i64
+; CHECK: %[[E:[^ ]*]] = ptrtoint i32* %[[X_GEP]] to i64
 ; CHECK: %[[F:[^ ]*]] = lshr i64 %[[E]], 4
 ; DYNAMIC-SHADOW: %[[X_SHADOW:[^ ]*]] = getelementptr i8, i8* %.hwasan.shadow, i64 %[[F]]
 ; ZERO-BASED-SHADOW: %[[X_SHADOW:[^ ]*]] = inttoptr i64 %[[F]] to i8*
-; CHECK: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW]], i8 %[[X_TAG2]], i64 1, i1 false)
+; CHECK: %[[X_SHADOW_GEP:[^ ]*]] = getelementptr i8, i8* %[[X_SHADOW]], i32 0
+; CHECK: store i8 4, i8* %[[X_SHADOW_GEP]]
+; CHECK: %[[X_I8:[^ ]*]] = bitcast i32* %[[X_GEP]] to i8*
+; CHECK: %[[X_I8_GEP:[^ ]*]] = getelementptr i8, i8* %[[X_I8]], i32 15
+; CHECK: store i8 %[[X_TAG2]], i8* %[[X_I8_GEP]]
 ; CHECK: call void @use32(i32* nonnull %[[X_HWASAN]])
 
 ; UAR-TAGS: %[[BASE_TAG_COMPL:[^ ]*]] = xor i64 %[[BASE_TAG]], 255
 ; UAR-TAGS: %[[X_TAG_UAR:[^ ]*]] = trunc i64 %[[BASE_TAG_COMPL]] to i8
-; CHECK: %[[E2:[^ ]*]] = ptrtoint i32* %[[X]] to i64
+; CHECK: %[[E2:[^ ]*]] = ptrtoint i32* %[[X_GEP]] to i64
 ; CHECK: %[[F2:[^ ]*]] = lshr i64 %[[E2]], 4
 ; DYNAMIC-SHADOW: %[[X_SHADOW2:[^ ]*]] = getelementptr i8, i8* %.hwasan.shadow, i64 %[[F2]]
 ; ZERO-BASED-SHADOW: %[[X_SHADOW2:[^ ]*]] = inttoptr i64 %[[F2]] to i8*
 ; NO-UAR-TAGS: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW2]], i8 0, i64 1, i1 false)
 ; UAR-TAGS: call void @llvm.memset.p0i8.i64(i8* align 1 %[[X_SHADOW2]], i8 %[[X_TAG_UAR]], i64 1, i1 false)
 ; CHECK: ret void
 
 
 entry:
   %x = alloca i32, align 4
   call void @use32(i32* nonnull %x)
   ret void
 }

llvm/test/Instrumentation/HWAddressSanitizer/basic.ll

 ; RECOVER: %[[B:[^ ]*]] = lshr i64 %[[A]], 56
 ; RECOVER: %[[PTRTAG:[^ ]*]] = trunc i64 %[[B]] to i8
 ; RECOVER: %[[C:[^ ]*]] = and i64 %[[A]], 72057594037927935
 ; RECOVER: %[[D:[^ ]*]] = lshr i64 %[[C]], 4
 ; RECOVER-DYNAMIC-SHADOW: %[[E:[^ ]*]] = getelementptr i8, i8* %.hwasan.shadow, i64 %4
 ; RECOVER-ZERO-BASED-SHADOW: %[[E:[^ ]*]] = inttoptr i64 %[[D]] to i8*
 ; RECOVER: %[[MEMTAG:[^ ]*]] = load i8, i8* %[[E]]
 ; RECOVER: %[[F:[^ ]*]] = icmp ne i8 %[[PTRTAG]], %[[MEMTAG]]
-; RECOVER: br i1 %[[F]], label {{.*}}, label {{.*}}, !prof {{.*}}
+; RECOVER: br i1 %[[F]], label %[[MISMATCH:[0-9]*]], label %[[CONT:[0-9]*]], !prof {{.*}}
+
+; RECOVER: [[MISMATCH]]:
+; RECOVER: %[[NOTSHORT:[^ ]*]] = icmp ugt i8 %[[MEMTAG]], 15
+; RECOVER: br i1 %[[NOTSHORT]], label %[[FAIL:[0-9]*]], label %[[SHORT:[0-9]*]], !prof {{.*}}
 
+; RECOVER: [[FAIL]]:
 ; RECOVER: call void asm sideeffect "brk #2336", "{x0}"(i64 %[[A]])
 ; RECOVER: br label
 
+; RECOVER: [[SHORT]]:
+; RECOVER: %[[LOWBITS:[^ ]*]] = and i64 %[[A]], 15
+; RECOVER: %[[LOWBITS_I8:[^ ]*]] = trunc i64 %[[LOWBITS]] to i8
+; RECOVER: %[[LAST:[^ ]*]] = add i8 %[[LOWBITS_I8]], 0
+; RECOVER: %[[OOB:[^ ]*]] = icmp uge i8 %[[LAST]], %[[MEMTAG]]
+; RECOVER: br i1 %[[OOB]], label %[[FAIL]], label %[[INBOUNDS:[0-9]*]], !prof {{.*}}
+
+; RECOVER: [[INBOUNDS]]:
+; RECOVER: %[[EOG_ADDR:[^ ]*]] = or i64 %[[C]], 15
+; RECOVER: %[[EOG_PTR:[^ ]*]] = inttoptr i64 %[[EOG_ADDR]] to i8*
+; RECOVER: %[[EOGTAG:[^ ]*]] = load i8, i8* %[[EOG_PTR]]
+; RECOVER: %[[EOG_MISMATCH:[^ ]*]] = icmp ne i8 %[[PTRTAG]], %[[EOGTAG]]
+; RECOVER: br i1 %[[EOG_MISMATCH]], label %[[FAIL]], label %[[CONT1:[0-9]*]], !prof {{.*}}
+
+; RECOVER: [[CONT1]]:
+; RECOVER: br label %[[CONT]]
+
+; RECOVER: [[CONT]]:
+
 ; ABORT-DYNAMIC-SHADOW: call void @llvm.hwasan.check.memaccess(i8* %.hwasan.shadow, i8* %a, i32 0)
 ; ABORT-ZERO-BASED-SHADOW: call void @llvm.hwasan.check.memaccess(i8* null, i8* %a, i32 0)
 
 ; CHECK: %[[G:[^ ]*]] = load i8, i8* %a, align 4
 ; CHECK: ret i8 %[[G]]
 
 entry:
   %b = load i8, i8* %a, align 4
   ret i8 %b
 }
 
 define i16 @test_load16(i16* %a) sanitize_hwaddress {
 ; CHECK-LABEL: @test_load16(
 ; RECOVER: %[[A:[^ ]*]] = ptrtoint i16* %a to i64
 ; RECOVER: %[[B:[^ ]*]] = lshr i64 %[[A]], 56
 ; RECOVER: %[[PTRTAG:[^ ]*]] = trunc i64 %[[B]] to i8
 ; RECOVER: %[[C:[^ ]*]] = and i64 %[[A]], 72057594037927935
 ; RECOVER: %[[D:[^ ]*]] = lshr i64 %[[C]], 4
 ; RECOVER-DYNAMIC-SHADOW: %[[E:[^ ]*]] = getelementptr i8, i8* %.hwasan.shadow, i64 %4
 ; RECOVER-ZERO-BASED-SHADOW: %[[E:[^ ]*]] = inttoptr i64 %[[D]] to i8*
 ; RECOVER: %[[MEMTAG:[^ ]*]] = load i8, i8* %[[E]]
 ; RECOVER: %[[F:[^ ]*]] = icmp ne i8 %[[PTRTAG]], %[[MEMTAG]]
-; RECOVER: br i1 %[[F]], label {{.*}}, label {{.*}}, !prof {{.*}}
+; RECOVER: br i1 %[[F]], label %[[MISMATCH:[0-9]*]], label %[[CONT:[0-9]*]], !prof {{.*}}
+
+; RECOVER: [[MISMATCH]]:
+; RECOVER: %[[NOTSHORT:[^ ]*]] = icmp ugt i8 %[[MEMTAG]], 15
+; RECOVER: br i1 %[[NOTSHORT]], label %[[FAIL:[0-9]*]], label %[[SHORT:[0-9]*]], !prof {{.*}}
 
+; RECOVER: [[FAIL]]:
 ; RECOVER: call void asm sideeffect "brk #2337", "{x0}"(i64 %[[A]])
 ; RECOVER: br label
 
+; RECOVER: [[SHORT]]:
+; RECOVER: %[[LOWBITS:[^ ]*]] = and i64 %[[A]], 15
+; RECOVER: %[[LOWBITS_I8:[^ ]*]] = trunc i64 %[[LOWBITS]] to i8
+; RECOVER: %[[LAST:[^ ]*]] = add i8 %[[LOWBITS_I8]], 1
+; RECOVER: %[[OOB:[^ ]*]] = icmp uge i8 %[[LAST]], %[[MEMTAG]]
+; RECOVER: br i1 %[[OOB]], label %[[FAIL]], label %[[INBOUNDS:[0-9]*]], !prof {{.*}}
+
+; RECOVER: [[INBOUNDS]]:
+; RECOVER: %[[EOG_ADDR:[^ ]*]] = or i64 %[[C]], 15
+; RECOVER: %[[EOG_PTR:[^ ]*]] = inttoptr i64 %[[EOG_ADDR]] to i8*
+; RECOVER: %[[EOGTAG:[^ ]*]] = load i8, i8* %[[EOG_PTR]]
+; RECOVER: %[[EOG_MISMATCH:[^ ]*]] = icmp ne i8 %[[PTRTAG]], %[[EOGTAG]]
+; RECOVER: br i1 %[[EOG_MISMATCH]], label %[[FAIL]], label %[[CONT1:[0-9]*]], !prof {{.*}}
+
+; RECOVER: [[CONT1]]:
+; RECOVER: br label %[[CONT]]
+
+; RECOVER: [[CONT]]:
+
 ; ABORT: %[[A:[^ ]*]] = bitcast i16* %a to i8*
 ; ABORT-DYNAMIC-SHADOW: call void @llvm.hwasan.check.memaccess(i8* %.hwasan.shadow, i8* %[[A]], i32 1)
 ; ABORT-ZERO-BASED-SHADOW: call void @llvm.hwasan.check.memaccess(i8* null, i8* %[[A]], i32 1)
 
 ; CHECK: %[[G:[^ ]*]] = load i16, i16* %a, align 4
 ; CHECK: ret i16 %[[G]]
 
 entry:

llvm/test/Instrumentation/HWAddressSanitizer/kernel-alloca.ll

 ; Test kernel hwasan instrumentation for alloca.
 ;
 ; RUN: opt < %s -hwasan -hwasan-kernel=1 -S | FileCheck %s
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 target triple = "aarch64--linux-android"
 
 declare void @use32(i32*)
 
 define void @test_alloca() sanitize_hwaddress {
 ; CHECK-LABEL: @test_alloca(
 ; CHECK: %[[FP:[^ ]*]] = call i8* @llvm.frameaddress(i32 0)
 ; CHECK: %[[A:[^ ]*]] = ptrtoint i8* %[[FP]] to i64
 ; CHECK: %[[B:[^ ]*]] = lshr i64 %[[A]], 20
 ; CHECK: %[[BASE_TAG:[^ ]*]] = xor i64 %[[A]], %[[B]]
 
-; CHECK: %[[X:[^ ]*]] = alloca i32, align 16
+; CHECK: %[[X:[^ ]*]] = alloca { i32, [12 x i8] }, align 16
+; CHECK: %[[X_GEP:[^ ]*]] = getelementptr { i32, [12 x i8] }, { i32, [12 x i8] }* %[[X]], i32 0, i32 0
 ; CHECK: %[[X_TAG:[^ ]*]] = xor i64 %[[BASE_TAG]], 0
-; CHECK: %[[X1:[^ ]*]] = ptrtoint i32* %[[X]] to i64
+; CHECK: %[[X1:[^ ]*]] = ptrtoint i32* %[[X_GEP]] to i64
 ; CHECK: %[[C:[^ ]*]] = shl i64 %[[X_TAG]], 56
 ; CHECK: %[[D:[^ ]*]] = or i64 %[[C]], 72057594037927935
 ; CHECK: %[[E:[^ ]*]] = and i64 %[[X1]], %[[D]]
 ; CHECK: %[[X_HWASAN:[^ ]*]] = inttoptr i64 %[[E]] to i32*
 
 entry:
   %x = alloca i32, align 4
   call void @use32(i32* nonnull %x)
   ret void
 }