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[msan] Add support for disable_sanitizer_instrumentation attribute

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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
This commit is contained in:
Alexander Potapenko 2021-08-17 11:34:22 +02:00
parent 791d88f35f
commit 8dc7dcdca1
3 changed files with 70 additions and 0 deletions
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9
clang/docs/MemorySanitizer.rst
View file

@ -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
----------

58
clang/test/CodeGen/sanitize-memory-disable.c Normal file
View file

@ -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;
}

3
llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
View file

@ -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.