[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.
git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176256 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/asan/asan_flags.h b/lib/asan/asan_flags.h
index 47c14aa..377354a 100644
--- a/lib/asan/asan_flags.h
+++ b/lib/asan/asan_flags.h
@@ -110,6 +110,9 @@
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();
diff --git a/lib/asan/asan_interceptors.cc b/lib/asan/asan_interceptors.cc
index e10a3b2..b1efe74 100644
--- a/lib/asan/asan_interceptors.cc
+++ b/lib/asan/asan_interceptors.cc
@@ -260,10 +260,26 @@
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));
}
diff --git a/lib/asan/asan_rtl.cc b/lib/asan/asan_rtl.cc
index 770e93a..d7aebd4 100644
--- a/lib/asan/asan_rtl.cc
+++ b/lib/asan/asan_rtl.cc
@@ -127,6 +127,7 @@
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 @@
// 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());
diff --git a/lib/asan/lit_tests/memcmp_strict_test.cc b/lib/asan/lit_tests/memcmp_strict_test.cc
new file mode 100644
index 0000000..00bf921
--- /dev/null
+++ b/lib/asan/lit_tests/memcmp_strict_test.cc
@@ -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;
+}
