[MSan] Add functions to enable/disable interceptor checks.

Summary:
The motivation for this change is to make libFuzzer+MSan possible
without instrumenting libFuzzer.

See https://github.com/google/sanitizers/issues/958.

Reviewers: eugenis

Reviewed By: eugenis

Subscribers: llvm-commits, kcc

Differential Revision: https://reviews.llvm.org/D48890

llvm-svn: 336447

compiler-rt/include/sanitizer/msan_interface.h

@@ -104,6 +104,14 @@ extern "C" {
      copy. Source and destination regions can overlap. */
   void __msan_copy_shadow(const volatile void *dst, const volatile void *src,
                           size_t size);
+
+  /* Disables uninitialized memory checks in interceptors. */
+  void __msan_scoped_disable_interceptor_checks(void);
+
+  /* Re-enables uninitialized memory checks in interceptors after a previous
+     call to __msan_scoped_disable_interceptor_checks. */
+  void __msan_scoped_enable_interceptor_checks(void);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

compiler-rt/lib/msan/msan_interceptors.cc

@@ -60,6 +60,9 @@ DECLARE_REAL(void *, memset, void *dest, int c, uptr n)
 // True if this is a nested interceptor.
 static THREADLOCAL int in_interceptor_scope;
 
+void __msan_scoped_disable_interceptor_checks() { ++in_interceptor_scope; }
+void __msan_scoped_enable_interceptor_checks() { --in_interceptor_scope; }
+
 struct InterceptorScope {
   InterceptorScope() { ++in_interceptor_scope; }
   ~InterceptorScope() { --in_interceptor_scope; }

compiler-rt/lib/msan/msan_interface_internal.h

@@ -174,6 +174,12 @@ void __msan_set_death_callback(void (*callback)(void));
 
 SANITIZER_INTERFACE_ATTRIBUTE
 void __msan_copy_shadow(void *dst, const void *src, uptr size);
+
+SANITIZER_INTERFACE_ATTRIBUTE
+void __msan_scoped_disable_interceptor_checks();
+
+SANITIZER_INTERFACE_ATTRIBUTE
+void __msan_scoped_enable_interceptor_checks();
 }  // extern "C"
 
 #endif  // MSAN_INTERFACE_INTERNAL_H

compiler-rt/test/msan/scoped-interceptors.cc

@@ -0,0 +1,52 @@
+// RUN: %clangxx_msan %s -o %t
+// RUN: %run %t --disable-checks 0 2>&1 | FileCheck --check-prefix=DISABLED --allow-empty %s
+// RUN: %run %t --disable-checks 1 2>&1 | FileCheck --check-prefix=DISABLED --allow-empty %s
+// RUN: %run %t --disable-checks 2 2>&1 | FileCheck --check-prefix=DISABLED --allow-empty %s
+// RUN: %run %t --disable-checks 3 2>&1 | FileCheck --check-prefix=DISABLED --allow-empty %s
+// RUN: not %run %t --reenable-checks 0 2>&1 | FileCheck --check-prefix=CASE-0 %s
+// RUN: not %run %t --reenable-checks 1 2>&1 | FileCheck --check-prefix=CASE-1 %s
+// RUN: not %run %t --reenable-checks 2 2>&1 | FileCheck --check-prefix=CASE-2 %s
+// RUN: not %run %t --reenable-checks 3 2>&1 | FileCheck --check-prefix=CASE-3 %s
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sanitizer/msan_interface.h>
+
+int main(int argc, char *argv[]) {
+  assert(argc == 3);
+  __msan_scoped_disable_interceptor_checks();
+  if (strcmp(argv[1], "--reenable-checks") == 0)
+    __msan_scoped_enable_interceptor_checks();
+
+  char uninit[7];
+  switch (argv[2][0]) {
+    case '0': {
+      char *copy = strndup(uninit, sizeof(uninit));  // BOOM
+      free(copy);
+      break;
+      // CASE-0: Uninitialized bytes in __interceptor_strndup
+    }
+    case '1': {
+      puts(uninit);  // BOOM
+      puts(uninit);  // Ensure previous call did not enable interceptor checks.
+      break;
+      // CASE-1: Uninitialized bytes in __interceptor_puts
+    }
+    case '2': {
+      int cmp = memcmp(uninit, uninit, sizeof(uninit));  // BOOM
+      break;
+      // CASE-2: Uninitialized bytes in __interceptor_memcmp
+    }
+    case '3': {
+      size_t len = strlen(uninit);  // BOOM
+      break;
+      // CASE-3: Uninitialized bytes in __interceptor_strlen
+    }
+    default: assert(0);
+  }
+  // DISABLED-NOT: Uninitialized bytes
+  return 0;
+}
+