[ASan] Added __asan_shadow_memory variable which points to the beginning of the shadow region using some assembly trickery.

[kstoimenov]

Summary

This is needed for the implementation of __asan_(load|store) in assembly as they need to know what is the beginning of the shadow region.

[kstoimenov]

/__asan_shadow_memory_offset/__asan_shadow_memory/

[kcc]

compiler-rt/lib/asan/asan_rtl.cpp

40

do you need an #ifdef here?

[kstoimenov]

compiler-rt/lib/asan/asan_rtl.cpp

40

In case asan_shadow_memory_dynamic_address is used I am not defining SHADOW_OFFSET_STR. The reason is that I will have to have a different assembly code and I didn't want to support it at this time. Because of the '#if defined' it will result in unresolved external if someone is trying to use shared optimized callbacks with asan_shadow_memory_dynamic_address.

[kcc]

LGTM, but please wait for Vitaly

[vitalybuka]

compiler-rt/lib/asan/asan_rtl.cpp

43

Why do you need globl and not address as a constant in asm?

44

Isn't this the same as SANITIZER_STRINGIFY(SHADOW_OFFSET)

[kstoimenov]

I found a better way to do this.

[delcypher]

compiler-rt/lib/asan/asan_mapping.h

187

It would be nice if we could "string-ifying" the existing constants here? E.g.

E.g.

 #define xstr(s) str(s)
 #define str(s) #s

...

#define SHADOW_OFFSET_STR xstr(SHADOW_OFFSET)

If you did something like that you only need to do #define SHADOW_OFFSET_STR once and you could hoist the definition out of the conditional macros.

Unfortunately it looks like that wouldn't work for things like kFreeBSD_ShadowOffset32 because those are global constants rather than macros.

Maybe there's another way to do it so we can avoid the duplication of constants?

compiler-rt/lib/asan/asan_interface_internal.h

extern "C" {
   SANITIZER_INTERFACE_ATTRIBUTE void __asan_print_accumulated_stats();
 
   SANITIZER_INTERFACE_ATTRIBUTE
   const char *__asan_default_options();
 
   SANITIZER_INTERFACE_ATTRIBUTE
   extern uptr __asan_shadow_memory_dynamic_address;
 
+  SANITIZER_INTERFACE_ATTRIBUTE
+  extern char __asan_shadow_memory;
+
   // Global flag, copy of ASAN_OPTIONS=detect_stack_use_after_return
   SANITIZER_INTERFACE_ATTRIBUTE
   extern int __asan_option_detect_stack_use_after_return;
 
   SANITIZER_INTERFACE_ATTRIBUTE
   extern uptr *__asan_test_only_reported_buggy_pointer;
 
   SANITIZER_INTERFACE_ATTRIBUTE void __asan_load1(uptr p);

compiler-rt/lib/asan/asan_mapping.h

 static const u64 kNetBSD_ShadowOffset32 = 1ULL << 30;  // 0x40000000
 static const u64 kNetBSD_ShadowOffset64 = 1ULL << 46;  // 0x400000000000
 static const u64 kWindowsShadowOffset32 = 3ULL << 28;  // 0x30000000
 
 #define SHADOW_SCALE kDefaultShadowScale
 
 #if SANITIZER_FUCHSIA
 #  define SHADOW_OFFSET (0)
+#  define SHADOW_OFFSET_STR "0"
 #elif SANITIZER_WORDSIZE == 32
 #  if SANITIZER_ANDROID
 #    define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
 #  elif defined(__mips__)
 #    define SHADOW_OFFSET kMIPS32_ShadowOffset32
+#    define SHADOW_OFFSET_STR "0xaaa0000"
 #  elif SANITIZER_FREEBSD
 #    define SHADOW_OFFSET kFreeBSD_ShadowOffset32
+#    define SHADOW_OFFSET_STR "0x40000000"
 #  elif SANITIZER_NETBSD
 #    define SHADOW_OFFSET kNetBSD_ShadowOffset32
+#    define SHADOW_OFFSET_STR "0x40000000"
 #  elif SANITIZER_WINDOWS
 #    define SHADOW_OFFSET kWindowsShadowOffset32
+#    define SHADOW_OFFSET_STR "0x30000000"
 #  elif SANITIZER_IOS
 #    define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
+#    define SHADOW_OFFSET_STR "0"
 #  else
 #    define SHADOW_OFFSET kDefaultShadowOffset32
+#    define SHADOW_OFFSET_STR "0x20000000"
 #  endif
 #else
 #  if SANITIZER_IOS
 #    define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
 #  elif SANITIZER_MAC && defined(__aarch64__)
 #    define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
 #elif SANITIZER_RISCV64
-#define SHADOW_OFFSET kRiscv64_ShadowOffset64
+#    define SHADOW_OFFSET kRiscv64_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0x55550000"
 #  elif defined(__aarch64__)
 #    define SHADOW_OFFSET kAArch64_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #  elif defined(__powerpc64__)
 #    define SHADOW_OFFSET kPPC64_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #  elif defined(__s390x__)
 #    define SHADOW_OFFSET kSystemZ_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #  elif SANITIZER_FREEBSD
 #    define SHADOW_OFFSET kFreeBSD_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #  elif SANITIZER_NETBSD
 #    define SHADOW_OFFSET kNetBSD_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #  elif SANITIZER_MAC
 #   define SHADOW_OFFSET kDefaultShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #  elif defined(__mips64)
-#   define SHADOW_OFFSET kMIPS64_ShadowOffset64
+#    define SHADOW_OFFSET kMIPS64_ShadowOffset64
+#    define SHADOW_OFFSET_STR "0"
 #elif defined(__sparc__)
 #define SHADOW_OFFSET kSPARC64_ShadowOffset64
 #  elif SANITIZER_WINDOWS64
-#   define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
+#    define SHADOW_OFFSET __asan_shadow_memory_dynamic_address
 #  else
-#   define SHADOW_OFFSET kDefaultShort64bitShadowOffset
+#    define SHADOW_OFFSET kDefaultShort64bitShadowOffset
+#    define SHADOW_OFFSET_STR "0x7fff8000"
 #  endif
 #endif
 
 #if SANITIZER_ANDROID && defined(__arm__)
 # define ASAN_PREMAP_SHADOW 1
 #else
 # define ASAN_PREMAP_SHADOW 0
 #endif

compiler-rt/lib/asan/asan_rtl.cpp

 #include "sanitizer_common/sanitizer_symbolizer.h"
 #include "ubsan/ubsan_init.h"
 #include "ubsan/ubsan_platform.h"
 
 uptr __asan_shadow_memory_dynamic_address;  // Global interface symbol.
 int __asan_option_detect_stack_use_after_return;  // Global interface symbol.
 uptr *__asan_test_only_reported_buggy_pointer;  // Used only for testing asan.
 
+// Defines a global pointer, which has SHADOW_OFFSET value.
+#if defined(SHADOW_OFFSET_STR)
+__asm(
+    ".section .bss ;"
+    ".globl __asan_shadow_memory ;"
+    ".set __asan_shadow_memory, " SHADOW_OFFSET_STR);
+#endif
+
 namespace __asan {
 
 uptr AsanMappingProfile[kAsanMappingProfileSize];
 
 static void AsanDie() {
   static atomic_uint32_t num_calls;
   if (atomic_fetch_add(&num_calls, 1, memory_order_relaxed) != 0) {
     // Don't die twice - run a busy loop.

compiler-rt/lib/asan/tests/asan_noinst_test.cpp

for (uptr is_write = 0; is_write <= 1; is_write++) {
             EXPECT_EQ(buggy_ptr, p + offset);
         }
       }
     }
     __asan::asan_free(ptr, &stack, __asan::FROM_MALLOC);
   }
   __asan_test_only_reported_buggy_pointer = 0;
 }
+
+#if defined(SHADOW_OFFSET_STR)
+TEST(AddressSanitizerInternalInterface, TestShadowGlobalVar) {
+  EXPECT_EQ((char *)SHADOW_OFFSET, &__asan_shadow_memory);
+}
+#endif