[MTE] Add AArch64GlobalsTagging Pass

[hctim]

Summary

Adds an IR pass for -fsanitize=memtag-globals. This pass goes over the
tag-capable global variables, and replaces them with a tagged global
variable of the same contents. This new global variable will have its
size and alignment adjusted if neccesary so that they're both a multiple
of the tag granule size (16 bytes).

Global merge must also be suppressed for tagged globals, as each global
variable must have a unique tag. This can possibly be relaxed in future;
globals that are identical in size, alignment, and content can possibly
be merged. The major problem comes from tail- or head-merging, which if
left unchecked, could have partially-overlapping global variables with
different memory tags, leading to crashes at runtime.

[fmayer]

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

61

not necessarily in this CL: do we want some attribute to turn off instrumentation?

99

can we use the SmallVector here?

109

what does this do?

[hctim]

Update from Florian's comments.

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

61

memtag sanitization is not-implicit (i.e. it's opt-in rather than opt-out): https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/IR/GlobalValue.h#L327, so a turn-off attribute should be unnecessary

109

dead code, thanks, removed

[tschuett]

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

93

If the 16 is the size of the granule, then it deserves to be named constant.

[hctim]

Update inlined constants to use named constant.

[fmayer]

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

26

why don't we put this into the llvm namespace rather than using?

[tschuett]

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

30

I believe you are going too far with the anonymous namespace. There is no need for static functions in anonymous namespaces.

https://llvm.org/docs/CodingStandards.html#anonymous-namespaces

[hctim]

Some namespace moving and shaking.

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

26

common for code in this folder, INITIALIZE_PASS_BEGIN (below) errors out not being in the llvm namespace, but also warns about redundantly using llvm:: in the macro expansion if you explicitly use the namespace...

30

moved everything but the class out of the namespace

93

thanks, done

[eugenis]

Change description says that the new pass "marks them as tagged". That's not what is happening.

llvm/lib/CodeGen/GlobalMerge.cpp

657

This comment is not convincing. The change description is right that some globals can be merged, copy that here, or extend the comment a little to explain why and under what assumptions.

llvm/lib/MC/ELFObjectWriter.cpp

1344

Isn't a bigger reason that we need to know the address tag to put on the pointer, and that requires a symbol, not a section reference?

[hctim]

Rebase now that the parent is submitted, clean up an old comment. New commit message also incoming.

llvm/lib/CodeGen/GlobalMerge.cpp

657

Thanks, extended the comment.

llvm/lib/MC/ELFObjectWriter.cpp

1344

removed this comment here, as this was moved into the parent patch https://reviews.llvm.org/D131863 and the comment was updated there. this comment references the old st_other-based implementation, whereas now it's needed for SHT_AARCH64_MEMTAG_GLOBALS_STATIC.

[hctim]

Rebase.

[eugenis]

LGTM

llvm/lib/CodeGen/GlobalMerge.cpp

656

typo: "merge"

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

76

unused variable

[hctim]

Rebase for submit.

[dyung]

Hi @hctim, the test you added is failing on buildbots where AArch64 is not built, can you either update the test to not require that backend, or mark the test as requiring it?

https://lab.llvm.org/buildbot/#/builders/139/builds/35253

error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-android31"'
1 error generated.

[hctim]

In D133392#4094524, @dyung wrote:

Hi @hctim, the test you added is failing on buildbots where AArch64 is not built, can you either update the test to not require that backend, or mark the test as requiring it?

https://lab.llvm.org/buildbot/#/builders/139/builds/35253

error: unable to create target: 'No available targets are compatible with triple "aarch64-unknown-linux-android31"'
1 error generated.

Thanks for the heads up. I've reverted and will test on my end before relanding.

clang/test/CodeGen/memtag-globals-asm.cpp

+// RUN: %clang_cc1 -S -x c++ -std=c++11 -triple aarch64-linux-android31 \
+// RUN:   -fsanitize=memtag-globals -o %t.out %s
+// RUN: FileCheck %s --input-file=%t.out
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-A
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-B
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-C
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-D
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-E
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-F
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-G
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-H
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-I
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-J
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-K
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-L
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-M
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-N
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-O
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-P
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-Q
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-R
+
+// RUN: %clang_cc1 -O3 -S -x c++ -std=c++11 -triple aarch64-linux-android31 \
+// RUN:   -fsanitize=memtag-globals -o %t.out %s
+// RUN: FileCheck %s --input-file=%t.out
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-A
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-B
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-C
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-D
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-E
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-F
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-G
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-H
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-I
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-J
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-K
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-L
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-M
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-N
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-O
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-P
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-Q
+// RUN: FileCheck %s --input-file=%t.out --check-prefix=CHECK-R
+
+/// Ensure that emulated TLS also doesn't get sanitized.
+// RUN: %clang_cc1 -S -x c++ -std=c++11 -triple aarch64-linux-android31 \
+// RUN:   -fsanitize=memtag-globals -o - %s | FileCheck %s
+
+// CHECK-A: .memtag global_int
+// CHECK-A: .globl global_int
+// CHECK-A: .p2align 4, 0x0
+// CHECK-A: .size global_int, 16
+int global_int;
+// CHECK-B: .memtag _ZL9local_int
+// CHECK-B: .local _ZL9local_int
+// CHECK-B: .comm _ZL9local_int,16,16
+static int local_int;
+
+// CHECK-C: .memtag _ZL12local_buffer
+// CHECK-C: .local _ZL12local_buffer
+// CHECK-C: .comm _ZL12local_buffer,16,16
+static char local_buffer[16];
+// CHECK-D: .memtag _ZL22local_buffer_local_end
+// CHECK-D: .p2align 4, 0x0
+// CHECK-D: _ZL22local_buffer_local_end:
+// CHECK-D: .xword _ZL12local_buffer+16
+// CHECK-D: .size _ZL22local_buffer_local_end, 16
+static char* local_buffer_local_end = &local_buffer[16];
+// CHECK-E: .memtag local_buffer_global_end
+// CHECK-E: .globl local_buffer_global_end
+// CHECK-E  .p2align 4, 0x0
+// CHECK-E: local_buffer_global_end:
+// CHECK-E: .xword _ZL12local_buffer+16
+// CHECK-E: .size local_buffer_global_end, 16
+char* local_buffer_global_end = &local_buffer[16];
+
+// CHECK-F: .memtag global_buffer
+// CHECK-F: .globl global_buffer
+// CHECK-F: .p2align 4, 0x0
+// CHECK-F: .size global_buffer, 16
+char global_buffer[16];
+// CHECK-G: .memtag _ZL23global_buffer_local_end
+// CHECK-G: .p2align 4, 0x0
+// CHECK-G: _ZL23global_buffer_local_end:
+// CHECK-G: .xword global_buffer+16
+// CHECK-G: .size _ZL23global_buffer_local_end, 16
+static char* global_buffer_local_end = &global_buffer[16];
+// CHECK-H: .memtag global_buffer_global_end
+// CHECK-H: .p2align 4, 0x0
+// CHECK-H: global_buffer_global_end:
+// CHECK-H: .xword global_buffer+16
+// CHECK-H: .size global_buffer_global_end, 16
+char* global_buffer_global_end = &global_buffer[16];
+
+class MyClass {
+ public:
+  virtual ~MyClass() {}
+  static int my_class_int;
+  static const int my_class_const_int;
+  virtual int virtual_func() { return 1; }
+};
+// CHECK-I: .memtag _ZN7MyClass12my_class_intE
+// CHECK-I: .globl _ZN7MyClass12my_class_intE
+// CHECK-I: .p2align 4, 0x0
+// CHECK-I: .size _ZN7MyClass12my_class_intE, 16
+int MyClass::my_class_int;
+// CHECK-NOT: .memtag _ZN7MyClass18my_class_const_intE
+const int MyClass::my_class_const_int = 1;
+
+// CHECK-J: .memtag global_my_class
+// CHECK-J: .globl global_my_class
+// CHECK-J: .p2align 4, 0x0
+// CHECK-J: .size global_my_class, 16
+MyClass global_my_class;
+// CHECK-K: .memtag _ZL14local_my_class
+// CHECK-K: .p2align 4, 0x0
+// CHECK-K: .size _ZL14local_my_class, 16
+static MyClass local_my_class;
+
+// CHECK-NOT: .memtag _ZL18local_const_string
+static const char local_const_string[] = "this is a local string";
+// CHECK-L: .memtag _ZL12local_string
+// CHECK-L: .p2align 4, 0x0
+// CHECK-L: .size _ZL12local_string, 32
+static char local_string[] = "this is a local string";
+
+// CHECK-M: .memtag global_atomic_int
+// CHECK-M: .globl global_atomic_int
+// CHECK-M: .p2align 4, 0x0
+// CHECK-M: .size global_atomic_int, 16
+_Atomic(int) global_atomic_int;
+// CHECK-N: .memtag _ZL16local_atomic_int
+// CHECK-N: .local _ZL16local_atomic_int
+// CHECK-N: .comm _ZL16local_atomic_int,16,16
+static _Atomic(int) local_atomic_int;
+
+union MyUnion {
+  int i;
+  char c;
+};
+
+// CHECK-O: .memtag global_union
+// CHECK-O: .globl global_union
+// CHECK-O: .p2align 4, 0x0
+// CHECK-O: .size global_union, 16
+MyUnion global_union;
+// CHECK-P: .memtag _ZL11local_union
+// CHECK-P: .local _ZL11local_union
+// CHECK-P: .comm _ZL11local_union,16,16
+static MyUnion local_union;
+
+// CHECK-NOT: .memtag {{.*}}global_tls
+thread_local int global_tls;
+// CHECK-NOT: .memtag {{.*}}local_tls
+static thread_local int local_tls;
+
+/// Prevent the compiler from realising that non-const local variables are not
+/// modified, and constant inlining into f().
+const void* export_pointers(int c) {
+  switch (c) {
+    case 0:  return &local_int;
+    case 1:  return &local_buffer;
+    case 2:  return &local_buffer_local_end;
+    case 3:  return &global_buffer_local_end;
+    case 4:  return &MyClass::my_class_int;
+    case 6:  return &local_my_class;
+    case 8:  return &local_string;
+    case 9:  return &local_atomic_int;
+    case 10: return &local_union;
+    case 11: return &local_tls;
+  }
+  return nullptr;
+}
+
+/// Ensure that all tagged globals are loaded/referenced via. the GOT.
+// CHECK-NOT:      .memtag _Z1fi
+// CHECK-Q:        _Z1fi:
+int f(int x) {
+  // CHECK-R: .memtag _ZZ1fiE12function_int
+  // CHECK-R: .local _ZZ1fiE12function_int
+  // CHECK-R: .comm _ZZ1fiE12function_int,16,16
+  static int function_int = 0;
+  /// Prevent non-const `f` from being promoted to a constant and inlined.
+  function_int += x;
+
+  return
+  // CHECK-Q-DAG: adrp [[REG_A:x[0-9]+]], :got:global_int
+  // CHECK-Q-DAG: ldr  [[REG_A2:x[0-9]+]], [[[REG_A]], :got_lo12:global_int]
+  // CHECK-Q-DAG: ldr  {{.*}}, [[[REG_A2]]]
+      global_int +
+  // CHECK-Q-DAG: adrp [[REG_B:x[0-9]+]], :got:_ZL9local_int
+  // CHECK-Q-DAG: ldr  [[REG_B2:x[0-9]+]], [[[REG_B]], :got_lo12:_ZL9local_int]
+  // CHECK-Q-DAG: ldr  {{.*}}, [[[REG_B2]]]
+      local_int +
+  // CHECK-Q-DAG: adrp  [[REG_C:x[0-9]+]], :got:_ZL12local_buffer
+  // CHECK-Q-DAG: ldr   [[REG_C2:x[0-9]+]], [[[REG_C]], :got_lo12:_ZL12local_buffer]
+  // CHECK-Q-DAG: ldrsb {{.*}}, [[[REG_C2]]]
+      local_buffer[0] +
+  // CHECK-Q-DAG: adrp   [[REG_D:x[0-9]+]], :got:_ZL22local_buffer_local_end
+  // CHECK-Q-DAG: ldr    [[REG_D2:x[0-9]+]], [[[REG_D]], :got_lo12:_ZL22local_buffer_local_end]
+  // CHECK-Q-DAG: ldr    [[REG_D3:x[0-9]+]], [[[REG_D2]]]
+  // CHECK-Q-DAG: ldursb {{.*}}, [[[REG_D3]], #-16]
+      local_buffer_local_end[-16] +
+  // CHECK-Q-DAG: adrp   [[REG_E:x[0-9]+]], :got:local_buffer_global_end
+  // CHECK-Q-DAG: ldr    [[REG_E2:x[0-9]+]], [[[REG_E]], :got_lo12:local_buffer_global_end]
+  // CHECK-Q-DAG: ldr    [[REG_E3:x[0-9]+]], [[[REG_E2]]]
+  // CHECK-Q-DAG: ldursb {{.*}}, [[[REG_E3]], #-16]
+      local_buffer_global_end[-16] +
+  // CHECK-Q-DAG: adrp  [[REG_F:x[0-9]+]], :got:global_buffer{{$}}
+  // CHECK-Q-DAG: ldr   [[REG_F2:x[0-9]+]], [[[REG_F]], :got_lo12:global_buffer]
+  // CHECK-Q-DAG: ldrsb {{.*}}, [[[REG_F2]]]
+      global_buffer[0] +
+  // CHECK-Q-DAG: adrp   [[REG_G:x[0-9]+]], :got:_ZL23global_buffer_local_end
+  // CHECK-Q-DAG: ldr    [[REG_G2:x[0-9]+]], [[[REG_G]], :got_lo12:_ZL23global_buffer_local_end]
+  // CHECK-Q-DAG: ldr    [[REG_G3:x[0-9]+]], [[[REG_G2]]]
+  // CHECK-Q-DAG: ldursb {{.*}}, [[[REG_G3]], #-16]
+      global_buffer_local_end[-16] +
+  // CHECK-Q-DAG: adrp   [[REG_H:x[0-9]+]], :got:global_buffer_global_end
+  // CHECK-Q-DAG: ldr    [[REG_H2:x[0-9]+]], [[[REG_H]], :got_lo12:global_buffer_global_end]
+  // CHECK-Q-DAG: ldr    [[REG_H3:x[0-9]+]], [[[REG_H2]]]
+  // CHECK-Q-DAG: ldursb {{.*}}, [[[REG_H3]], #-16]
+      global_buffer_global_end[-16] +
+  // CHECK-Q-DAG: adrp [[REG_I:x[0-9]+]], :got:_ZN7MyClass12my_class_intE
+  // CHECK-Q-DAG: ldr  [[REG_I2:x[0-9]+]], [[[REG_I]], :got_lo12:_ZN7MyClass12my_class_intE]
+  // CHECK-Q-DAG: ldr  {{.*}}, [[[REG_I2]]]
+      MyClass::my_class_int +
+  /// Constant values - ignore.
+      MyClass::my_class_const_int +
+      global_my_class.virtual_func() +
+      local_my_class.virtual_func() +
+      local_const_string[0] +
+  // CHECK-Q-DAG: adrp  [[REG_J:x[0-9]+]], :got:_ZL12local_string
+  // CHECK-Q-DAG: ldr   [[REG_J2:x[0-9]+]], [[[REG_J]], :got_lo12:_ZL12local_string]
+  // CHECK-Q-DAG: ldrsb {{.*}}, [[[REG_J2]]]
+      local_string[0] +
+  // CHECK-Q-DAG: adrp  [[REG_K:x[0-9]+]], :got:_ZL16local_atomic_int
+  // CHECK-Q-DAG: ldr   [[REG_K2:x[0-9]+]], [[[REG_K]], :got_lo12:_ZL16local_atomic_int]
+  // CHECK-Q-DAG: ldar {{.*}}, [[[REG_K2]]]
+      local_atomic_int +
+  // CHECK-Q-DAG: adrp [[REG_L:x[0-9]+]], :got:global_atomic_int
+  // CHECK-Q-DAG: ldr  [[REG_L2:x[0-9]+]], [[[REG_L]], :got_lo12:global_atomic_int]
+  // CHECK-Q-DAG: ldar {{.*}}, [[[REG_L2]]]
+      global_atomic_int +
+  // CHECK-Q-DAG: adrp [[REG_M:x[0-9]+]], :got:global_union
+  // CHECK-Q-DAG: ldr  [[REG_M2:x[0-9]+]], [[[REG_M]], :got_lo12:global_union]
+  // CHECK-Q-DAG: ldr  {{.*}}, [[[REG_M2]]]
+      global_union.i +
+  // CHECK-Q-DAG: adrp  [[REG_N:x[0-9]+]], :got:_ZL11local_union
+  // CHECK-Q-DAG: ldr   [[REG_N2:x[0-9]+]], [[[REG_N]], :got_lo12:_ZL11local_union]
+  // CHECK-Q-DAG: ldrsb {{.*}}, [[[REG_N2]]]
+      local_union.c +
+  /// Global variables - ignore.
+      global_tls +
+      local_tls +
+  // CHECK-Q-DAG: adrp  [[REG_O:x[0-9]+]], :got:_ZZ1fiE12function_int
+  // CHECK-Q-DAG: ldr   [[REG_O2:x[0-9]+]], [[[REG_O]], :got_lo12:_ZZ1fiE12function_int]
+  // CHECK-Q-DAG: ldr   {{.*}}, [[[REG_O2]]]
+      function_int;
+}

llvm/lib/CodeGen/GlobalMerge.cpp

for (auto &GV : M.globals()) {
     if (GV.getName().startswith("llvm.") ||
         GV.getName().startswith(".llvm."))
       continue;
 
     // Ignore all "required" globals:
     if (isMustKeepGlobalVariable(&GV))
       continue;
 
+    // Tagged global variables shouldn't be merged, as they are assigned unique
+    // memory tags at runtime.
+    if (GV.isTagged())
+      continue;
+
     Type *Ty = GV.getValueType();
     if (DL.getTypeAllocSize(Ty) < MaxOffset) {
       if (TM &&
           TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSS())
         BSSGlobals[{AddressSpace, Section}].push_back(&GV);
       else if (GV.isConstant())
         ConstGlobals[{AddressSpace, Section}].push_back(&GV);
       else

llvm/lib/MC/ELFObjectWriter.cpp

if (Sym->isMemtag())
     return true;
 
   // An undefined symbol is not in any section, so the relocation has to point
   // to the symbol itself.
   assert(Sym && "Expected a symbol");
   if (Sym->isUndefined())
     return true;
 
+  // For memory-tagged symbols, ensure that the relocation uses the symbol. For
+  // tagged symbols, the linker needs to know whether to emit a special addend
+  // when relocating `end` symbols, and this can only be determined by the
+  // attributes of the symbol itself.
+  if (Sym->isMemtag())
+    return true;
+
   unsigned Binding = Sym->getBinding();
   switch(Binding) {
   default:
     llvm_unreachable("Invalid Binding");
   case ELF::STB_LOCAL:
     break;
   case ELF::STB_WEAK:
     // If the symbol is weak, it might be overridden by a symbol in another

llvm/lib/Target/AArch64/AArch64.h

createAArch64InstructionSelector(const AArch64TargetMachine &,
                                  AArch64Subtarget &, AArch64RegisterBankInfo &);
 FunctionPass *createAArch64O0PreLegalizerCombiner();
 FunctionPass *createAArch64PreLegalizerCombiner();
 FunctionPass *createAArch64PostLegalizerCombiner(bool IsOptNone);
 FunctionPass *createAArch64PostLegalizerLowering();
 FunctionPass *createAArch64PostSelectOptimize();
 FunctionPass *createAArch64StackTaggingPass(bool IsOptNone);
 FunctionPass *createAArch64StackTaggingPreRAPass();
+ModulePass *createAArch64GlobalsTaggingPass();
 
 void initializeAArch64A53Fix835769Pass(PassRegistry&);
 void initializeAArch64A57FPLoadBalancingPass(PassRegistry&);
 void initializeAArch64AdvSIMDScalarPass(PassRegistry&);
 void initializeAArch64BranchTargetsPass(PassRegistry&);
 void initializeAArch64CFIFixupPass(PassRegistry&);
 void initializeAArch64CollectLOHPass(PassRegistry&);
 void initializeAArch64CondBrTuningPass(PassRegistry &);
 void initializeAArch64CompressJumpTablesPass(PassRegistry&);
 void initializeAArch64ConditionalComparesPass(PassRegistry&);
 void initializeAArch64ConditionOptimizerPass(PassRegistry&);
 void initializeAArch64DeadRegisterDefinitionsPass(PassRegistry&);
 void initializeAArch64ExpandPseudoPass(PassRegistry&);
+void initializeAArch64GlobalsTaggingPass(PassRegistry &);
 void initializeAArch64SLSHardeningPass(PassRegistry&);
 void initializeAArch64SpeculationHardeningPass(PassRegistry&);
 void initializeAArch64KCFIPass(PassRegistry &);
 void initializeAArch64LoadStoreOptPass(PassRegistry&);
 void initializeAArch64LowerHomogeneousPrologEpilogPass(PassRegistry &);
 void initializeAArch64MIPeepholeOptPass(PassRegistry &);
 void initializeAArch64SIMDInstrOptPass(PassRegistry&);
 void initializeAArch64O0PreLegalizerCombinerPass(PassRegistry &);

llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp

+//===- AArch64GlobalsTagging.cpp - Global tagging in IR -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//===----------------------------------------------------------------------===//
+
+#include "AArch64.h"
+#include "llvm/BinaryFormat/ELF.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include <algorithm>
+#include <set>
+
+using namespace llvm;
+
+static const Align kTagGranuleSize = Align(16);
+
+namespace {
+
+class AArch64GlobalsTagging : public ModulePass {
+public:
+  static char ID;
+
+  explicit AArch64GlobalsTagging() : ModulePass(ID) {
+    initializeAArch64GlobalsTaggingPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnModule(Module &M) override;
+
+  StringRef getPassName() const override { return "AArch64 Globals Tagging"; }
+
+private:
+  std::set<GlobalVariable *> GlobalsToTag;
+};
+
+char AArch64GlobalsTagging::ID = 0;
+
+static bool shouldTagGlobal(GlobalVariable &G) {
+  if (!G.isTagged())
+    return false;
+
+  assert(G.hasSanitizerMetadata() &&
+         "Missing sanitizer metadata, but symbol is apparently tagged.");
+  GlobalValue::SanitizerMetadata Meta = G.getSanitizerMetadata();
+
+  // For now, don't instrument constant data, as it'll be in .rodata anyway. It
+  // may be worth instrumenting these in future to stop them from being used as
+  // gadgets.
+  if (G.getName().startswith("llvm.") || G.isThreadLocal() || G.isConstant()) {
+    Meta.Memtag = false;
+    G.setSanitizerMetadata(Meta);
+    return false;
+  }
+
+  return true;
+}
+
+// Technically, due to ELF symbol interposition semantics, we can't change the
+// alignment or size of symbols. If we increase the alignment or size of a
+// symbol, the compiler may make optimisations based on this new alignment or
+// size. If the symbol is interposed, this optimisation could lead to
+// alignment-related or OOB read/write crashes.
+//
+// This is handled in the linker. When the linker sees multiple declarations of
+// a global variable, and some are tagged, and some are untagged, it resolves it
+// to be an untagged definition - but preserves the tag-granule-rounded size and
+// tag-granule-alignment. This should prevent these kind of crashes intra-DSO.
+// For cross-DSO, it's been a reasonable contract that if you're interposing a
+// sanitizer-instrumented global, then the interposer also needs to be
+// sanitizer-instrumented.
+//
+// FIXME: In theory, this can be fixed by splitting the size/alignment of
+// globals into two uses: an "output alignment" that's emitted to the ELF file,
+// and an "optimisation alignment" that's used for optimisation. Thus, we could
+// adjust the output alignment only, and still optimise based on the pessimistic
+// pre-tagging size/alignment.
+static void tagGlobalDefinition(Module &M, GlobalVariable *G) {
+  Constant *Initializer = G->getInitializer();
+  uint64_t SizeInBytes =
+      M.getDataLayout().getTypeAllocSize(Initializer->getType());
+
+  uint64_t NewSize = alignTo(SizeInBytes, 16);
+  if (SizeInBytes != NewSize) {
+    DataLayout NewLayout = M.getDataLayout();
+
+    // Pad the initializer out to the next multiple of 16 bytes.
+    llvm::SmallVector<uint8_t> Init(NewSize - SizeInBytes, 0);
+    Constant *Padding = ConstantDataArray::get(M.getContext(), Init);
+    Initializer = ConstantStruct::getAnon({Initializer, Padding});
+    auto *NewGV = new GlobalVariable(
+        M, Initializer->getType(), G->isConstant(), G->getLinkage(),
+        Initializer, "", G, G->getThreadLocalMode(), G->getAddressSpace());
+    NewGV->copyAttributesFrom(G);
+    NewGV->setComdat(G->getComdat());
+    NewGV->copyMetadata(G, 0);
+
+    NewGV->takeName(G);
+    G->replaceAllUsesWith(NewGV);
+    G->eraseFromParent();
+    G = NewGV;
+  }
+
+  G->setAlignment(std::max(G->getAlign().valueOrOne(), kTagGranuleSize));
+
+  // Ensure that tagged globals don't get merged by ICF - as they should have
+  // different tags at runtime.
+  G->setUnnamedAddr(GlobalValue::UnnamedAddr::None);
+}
+
+bool AArch64GlobalsTagging::runOnModule(Module &M) {
+  // No mutating the globals in-place, or iterator invalidation occurs.
+  std::vector<GlobalVariable *> GlobalsToTag;
+  for (GlobalVariable &G : M.globals()) {
+    if (G.isDeclaration() || !shouldTagGlobal(G))
+      continue;
+    GlobalsToTag.push_back(&G);
+  }
+
+  for (GlobalVariable *G : GlobalsToTag) {
+    tagGlobalDefinition(M, G);
+  }
+
+  return true;
+}
+
+} // anonymous namespace
+
+INITIALIZE_PASS_BEGIN(AArch64GlobalsTagging, "aarch64-globals-tagging",
+                      "AArch64 Globals Tagging Pass", false, false)
+INITIALIZE_PASS_END(AArch64GlobalsTagging, "aarch64-globals-tagging",
+                    "AArch64 Globals Tagging Pass", false, false)
+
+ModulePass *llvm::createAArch64GlobalsTaggingPass() {
+  return new AArch64GlobalsTagging();
+}

llvm/lib/Target/AArch64/AArch64Subtarget.cpp

 unsigned
 AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
                                           const TargetMachine &TM) const {
   // MachO large model always goes via a GOT, simply to get a single 8-byte
   // absolute relocation on all global addresses.
   if (TM.getCodeModel() == CodeModel::Large && isTargetMachO())
     return AArch64II::MO_GOT;
 
+  // All globals dynamically protected by MTE must have their address tags
+  // synthesized. This is done by having the loader stash the tag in the GOT
+  // entry. Force all tagged globals (even ones with internal linkage) through
+  // the GOT.
+  if (GV->isTagged())
+    return AArch64II::MO_GOT;
+
   if (!TM.shouldAssumeDSOLocal(*GV->getParent(), GV)) {
     if (GV->hasDLLImportStorageClass())
       return AArch64II::MO_GOT | AArch64II::MO_DLLIMPORT;
     if (getTargetTriple().isOSWindows())
       return AArch64II::MO_GOT | AArch64II::MO_COFFSTUB;
     return AArch64II::MO_GOT;
   }
 

llvm/lib/Target/AArch64/AArch64TargetMachine.cpp

extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64Target() {
   initializeFalkorMarkStridedAccessesLegacyPass(*PR);
   initializeLDTLSCleanupPass(*PR);
   initializeSVEIntrinsicOptsPass(*PR);
   initializeAArch64SpeculationHardeningPass(*PR);
   initializeAArch64SLSHardeningPass(*PR);
   initializeAArch64StackTaggingPass(*PR);
   initializeAArch64StackTaggingPreRAPass(*PR);
   initializeAArch64LowerHomogeneousPrologEpilogPass(*PR);
+  initializeAArch64GlobalsTaggingPass(*PR);
 }
 
 //===----------------------------------------------------------------------===//
 // AArch64 Lowering public interface.
 //===----------------------------------------------------------------------===//
 static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
   if (TT.isOSBinFormatMachO())
     return std::make_unique<AArch64_MachoTargetObjectFile>();
if (TM->getOptLevel() == CodeGenOpt::Aggressive && EnableGEPOpt) {
     addPass(createEarlyCSEPass());
     // Do loop invariant code motion in case part of the lowered result is
     // invariant.
     addPass(createLICMPass());
   }
 
   TargetPassConfig::addIRPasses();
 
+  addPass(createAArch64GlobalsTaggingPass());
   addPass(createAArch64StackTaggingPass(
       /*IsOptNone=*/TM->getOptLevel() == CodeGenOpt::None));
 
   // Match interleaved memory accesses to ldN/stN intrinsics.
   if (TM->getOptLevel() != CodeGenOpt::None) {
     addPass(createInterleavedLoadCombinePass());
     addPass(createInterleavedAccessPass());
   }

llvm/lib/Target/AArch64/CMakeLists.txt

add_llvm_target(AArch64CodeGen
   AArch64ConditionalCompares.cpp
   AArch64DeadRegisterDefinitionsPass.cpp
   AArch64ExpandImm.cpp
   AArch64ExpandPseudoInsts.cpp
   AArch64FalkorHWPFFix.cpp
   AArch64FastISel.cpp
   AArch64A53Fix835769.cpp
   AArch64FrameLowering.cpp
+  AArch64GlobalsTagging.cpp
   AArch64CompressJumpTables.cpp
   AArch64ConditionOptimizer.cpp
   AArch64RedundantCopyElimination.cpp
   AArch64ISelDAGToDAG.cpp
   AArch64ISelLowering.cpp
   AArch64InstrInfo.cpp
   AArch64KCFI.cpp
   AArch64LoadStoreOptimizer.cpp

llvm/test/CodeGen/AArch64/O0-pipeline.ll

 ; CHECK-NEXT:       Module Verifier
 ; CHECK-NEXT:       Lower Garbage Collection Instructions
 ; CHECK-NEXT:       Shadow Stack GC Lowering
 ; CHECK-NEXT:       Lower constant intrinsics
 ; CHECK-NEXT:       Remove unreachable blocks from the CFG
 ; CHECK-NEXT:       Expand vector predication intrinsics
 ; CHECK-NEXT:       Scalarize Masked Memory Intrinsics
 ; CHECK-NEXT:       Expand reduction intrinsics
+; CHECK-NEXT:     AArch64 Globals Tagging
+; CHECK-NEXT:     FunctionPass Manager
 ; CHECK-NEXT:       AArch64 Stack Tagging
 ; CHECK-NEXT:       Exception handling preparation
 ; CHECK-NEXT:       Safe Stack instrumentation pass
 ; CHECK-NEXT:       Insert stack protectors
 ; CHECK-NEXT:       Module Verifier
 ; CHECK-NEXT:       Analysis containing CSE Info
 ; CHECK-NEXT:       IRTranslator
 ; CHECK-NEXT:       Analysis for ComputingKnownBits

llvm/test/CodeGen/AArch64/O3-pipeline.ll

 ; CHECK-NEXT:       Constant Hoisting
 ; CHECK-NEXT:       Replace intrinsics with calls to vector library
 ; CHECK-NEXT:       Partially inline calls to library functions
 ; CHECK-NEXT:       Expand vector predication intrinsics
 ; CHECK-NEXT:       Scalarize Masked Memory Intrinsics
 ; CHECK-NEXT:       Expand reduction intrinsics
 ; CHECK-NEXT:       Natural Loop Information
 ; CHECK-NEXT:       TLS Variable Hoist
+; CHECK-NEXT:     AArch64 Globals Tagging
 ; CHECK-NEXT:     Stack Safety Analysis
 ; CHECK-NEXT:       FunctionPass Manager
 ; CHECK-NEXT:         Dominator Tree Construction
 ; CHECK-NEXT:         Natural Loop Information
 ; CHECK-NEXT:         Scalar Evolution Analysis
 ; CHECK-NEXT:         Stack Safety Local Analysis
 ; CHECK-NEXT:     FunctionPass Manager
 ; CHECK-NEXT:       Dominator Tree Construction