[llvm] 8dc7dcd - [msan] Add support for disable_sanitizer_instrumentation attribute

[Alexander Potapenko via llvm-commits]

Author: Alexander Potapenko
Date: 2021-08-20T15:11:26+02:00
New Revision: 8dc7dcdca1e0d0ce4e39305272c8021a1aed07ed

URL: https://github.com/llvm/llvm-project/commit/8dc7dcdca1e0d0ce4e39305272c8021a1aed07ed
DIFF: https://github.com/llvm/llvm-project/commit/8dc7dcdca1e0d0ce4e39305272c8021a1aed07ed.diff

LOG: [msan] Add support for disable_sanitizer_instrumentation attribute

Unlike __attribute__((no_sanitize("memory"))), this one will cause MSan
to skip the entire function during instrumentation.

Depends on https://reviews.llvm.org/D108029

Differential Revision: https://reviews.llvm.org/D108199

Added: 
    clang/test/CodeGen/sanitize-memory-disable.c

Modified: 
    clang/docs/MemorySanitizer.rst
    llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/MemorySanitizer.rst b/clang/docs/MemorySanitizer.rst
index 3ba5ce5bed3e..c6fc9407ea15 100644
--- a/clang/docs/MemorySanitizer.rst
+++ b/clang/docs/MemorySanitizer.rst
@@ -85,6 +85,15 @@ particular function.  MemorySanitizer may still instrument such functions to
 avoid false positives.  This attribute may not be supported by other compilers,
 so we suggest to use it together with ``__has_feature(memory_sanitizer)``.
 
+``__attribute__((disable_sanitizer_instrumentation))``
+--------------------------------------------------------
+
+The ``disable_sanitizer_instrumentation`` attribute can be applied to functions
+to prevent all kinds of instrumentation. As a result, it may introduce false
+positives and therefore should be used with care, and only if absolutely
+required; for example for certain code that cannot tolerate any instrumentation
+and resulting side-effects. This attribute overrides ``no_sanitize("memory")``.
+
 Ignorelist
 ----------
 

diff  --git a/clang/test/CodeGen/sanitize-memory-disable.c b/clang/test/CodeGen/sanitize-memory-disable.c
new file mode 100644
index 000000000000..5bf4dc9c185e
--- /dev/null
+++ b/clang/test/CodeGen/sanitize-memory-disable.c
@@ -0,0 +1,58 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck -check-prefixes CHECK,WITHOUT %s
+// RUN: %clang_cc1 -emit-llvm -o - %s -fsanitize=memory | FileCheck -check-prefixes CHECK,MSAN %s
+// RUN: %clang_cc1 -emit-llvm -o - %s -fsanitize=kernel-memory | FileCheck -check-prefixes CHECK,KMSAN %s
+
+// Instrumented function.
+// MSan uses memset(addr, -1, size) to poison allocas and stores shadow of the return value in
+// __msan_retval_tls. KMSAN uses __msan_poison_alloca() to poison allocas and calls
+// __msan_get_context_state() at function prologue to access the task context struct (including the
+// shadow of the return value).
+//
+// CHECK-LABEL: i32 @instrumented1
+// KMSAN: __msan_get_context_state
+// WITHOUT-NOT: __msan_poison_alloca
+// WITHOUT-NOT: @llvm.memset
+// MSAN: @llvm.memset{{.*}}({{.*}}, i8 -1
+// KMSAN: __msan_poison_alloca
+// WITHOUT-NOT: __msan_retval_tls
+// MSAN: __msan_retval_tls
+// CHECK: ret i32
+int instrumented1(int *a) {
+  volatile char buf[8];
+  return *a;
+}
+
+// Function with no_sanitize("memory")/no_sanitize("kernel-memory"): no shadow propagation, but
+// unpoisons memory to prevent false positives.
+// MSan uses memset(addr, 0, size) to unpoison locals, KMSAN uses __msan_unpoison_alloca(). Both
+// tools still access the retval shadow to write 0 to it.
+//
+// CHECK-LABEL: i32 @no_false_positives1
+// KMSAN: __msan_get_context_state
+// WITHOUT-NOT: __msan_unpoison_alloca
+// WITHOUT-NOT: @llvm.memset
+// MSAN: @llvm.memset{{.*}}({{.*}}, i8 0
+// KMSAN: __msan_unpoison_alloca
+// WITHOUT-NOT: __msan_retval_tls
+// MSAN: __msan_retval_tls
+// CHECK: ret i32
+__attribute__((no_sanitize("memory"))) __attribute__((no_sanitize("kernel-memory"))) int no_false_positives1(int *a) {
+  volatile char buf[8];
+  return *a;
+}
+
+// Function with disable_sanitizer_instrumentation: no instrumentation at all.
+//
+// CHECK-LABEL: i32 @no_instrumentation1
+// KMSAN-NOT: __msan_get_context_state
+// WITHOUT-NOT: __msan_poison_alloca
+// WITHOUT-NOT: @llvm.memset
+// MSAN-NOT: @llvm.memset{{.*}}({{.*}}, i8 0
+// KMSAN-NOT: __msan_unpoison_alloca
+// WITHOUT-NOT: __msan_retval_tls
+// MSAN-NOT: __msan_retval_tls
+// CHECK: ret i32
+__attribute__((disable_sanitizer_instrumentation)) int no_instrumentation1(int *a) {
+  volatile char buf[8];
+  return *a;
+}

diff  --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 7e6709be4bbf..9b4cc9c46f45 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -5330,6 +5330,9 @@ bool MemorySanitizer::sanitizeFunction(Function &F, TargetLibraryInfo &TLI) {
   if (!CompileKernel && F.getName() == kMsanModuleCtorName)
     return false;
 
+  if (F.hasFnAttribute(Attribute::DisableSanitizerInstrumentation))
+    return false;
+
   MemorySanitizerVisitor Visitor(F, *this, TLI);
 
   // Clear out readonly/readnone attributes.