[PATCH] D108199: [msan] Add support for disable_sanitizer_instrumentation attribute

[Alexander Potapenko via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG8dc7dcdca1e0: [msan] Add support for disable_sanitizer_instrumentation attribute (authored by glider).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D108199/new/

https://reviews.llvm.org/D108199

Files:
  clang/docs/MemorySanitizer.rst
  clang/test/CodeGen/sanitize-memory-disable.c
  llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp


Index: llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -5330,6 +5330,9 @@
   if (!CompileKernel && F.getName() == kMsanModuleCtorName)
     return false;
 
+  if (F.hasFnAttribute(Attribute::DisableSanitizerInstrumentation))
+    return false;
+
   MemorySanitizerVisitor Visitor(F, *this, TLI);
 
   // Clear out readonly/readnone attributes.
Index: clang/test/CodeGen/sanitize-memory-disable.c
===================================================================
--- /dev/null
+++ 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;
+}
Index: clang/docs/MemorySanitizer.rst
===================================================================
--- clang/docs/MemorySanitizer.rst
+++ clang/docs/MemorySanitizer.rst
@@ -85,6 +85,15 @@
 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
 ----------
 


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