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[ASan] Add the memcmp_strict flag (1 by default) that controls the behavior of accessibility checks in memcmp. 

1: memcmp(p1, p2, n) always checks n bytes
0: memcmp checks up to n bytes depending on whether the memory contents differ.

llvm-svn: 176256
This commit is contained in:
Alexander Potapenko 2013-02-28 14:09:30 +00:00
parent 1cb95a17b8
commit f1c48eb509
4 changed files with 41 additions and 4 deletions
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3
compiler-rt/lib/asan/asan_flags.h
View File

@ -110,6 +110,9 @@ struct Flags {
bool alloc_dealloc_mismatch;
// Use stack depot instead of storing stacks in the redzones.
bool use_stack_depot;
// If true, assume that memcmp(p1, p2, n) always reads n bytes before
// comparing p1 and p2.
bool strict_memcmp;
};
Flags *flags();

24
compiler-rt/lib/asan/asan_interceptors.cc
View File

@ -260,10 +260,26 @@ INTERCEPTOR(int, memcmp, const void *a1, const void *a2, uptr size) {
if (!asan_inited) return internal_memcmp(a1, a2, size);
ENSURE_ASAN_INITED();
if (flags()->replace_intrin) {
// We check the entire regions even if the first bytes of the buffers
// are different.
ASAN_READ_RANGE(a1, size);
ASAN_READ_RANGE(a2, size);
if (flags()->strict_memcmp) {
// Check the entire regions even if the first bytes of the buffers are
// different.
ASAN_READ_RANGE(a1, size);
ASAN_READ_RANGE(a2, size);
// Fallthrough to REAL(memcmp) below.
} else {
unsigned char c1 = 0, c2 = 0;
const unsigned char *s1 = (const unsigned char*)a1;
const unsigned char *s2 = (const unsigned char*)a2;
uptr i;
for (i = 0; i < size; i++) {
c1 = s1[i];
c2 = s2[i];
if (c1 != c2) break;
}
ASAN_READ_RANGE(s1, Min(i + 1, size));
ASAN_READ_RANGE(s2, Min(i + 1, size));
return CharCmp(c1, c2);
}
}
return REAL(memcmp(a1, a2, size));
}

2
compiler-rt/lib/asan/asan_rtl.cc
View File

@ -127,6 +127,7 @@ static void ParseFlagsFromString(Flags *f, const char *str) {
ParseFlag(str, &f->poison_heap, "poison_heap");
ParseFlag(str, &f->alloc_dealloc_mismatch, "alloc_dealloc_mismatch");
ParseFlag(str, &f->use_stack_depot, "use_stack_depot");
ParseFlag(str, &f->strict_memcmp, "strict_memcmp");
}
void InitializeFlags(Flags *f, const char *env) {
@ -168,6 +169,7 @@ void InitializeFlags(Flags *f, const char *env) {
// TODO(glider): Fix known issues and enable this back.
f->alloc_dealloc_mismatch = (ASAN_MAC == 0);;
f->use_stack_depot = true; // Only affects allocator2.
f->strict_memcmp = true;
// Override from compile definition.
ParseFlagsFromString(f, MaybeUseAsanDefaultOptionsCompileDefiniton());

16
compiler-rt/lib/asan/lit_tests/memcmp_strict_test.cc Normal file
View File

@ -0,0 +1,16 @@
// RUN: %clangxx_asan -m64 -O0 %s -o %t && ASAN_OPTIONS=strict_memcmp=0 %t 2>&1 | %symbolize | FileCheck %s --check-prefix=CHECK-nonstrict
// RUN: %clangxx_asan -m64 -O0 %s -o %t && ASAN_OPTIONS=strict_memcmp=1 %t 2>&1 | %symbolize | FileCheck %s --check-prefix=CHECK-strict
// Default to strict_memcmp=1.
// RUN: %clangxx_asan -m64 -O0 %s -o %t && %t 2>&1 | %symbolize | FileCheck %s --check-prefix=CHECK-strict
#include <stdio.h>
#include <string.h>
int main() {
char kFoo[] = "foo";
char kFubar[] = "fubar";
int res = memcmp(kFoo, kFubar, strlen(kFubar));
printf("res: %d\n", res);
// CHECK-nonstrict: {{res: -1}}
// CHECK-strict: AddressSanitizer: stack-buffer-overflow
return 0;
}