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

[morehouse]

Summary

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

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

[eugenis]

I'd prefer
msan_scoped_enable_interceptor_checks
msan_scoped_disable_interceptor_checks
(without "re")
Please add tests.

[morehouse]

• Add _scoped_ to function names.
• Add test.

[eugenis]

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

33

repeat this line one more time to make sure that the first call did not somehow re-enable interceptor checks.

[morehouse]

• Repeat puts().

compiler-rt/include/sanitizer/msan_interface.h

#endif
   void __msan_set_death_callback(void (*callback)(void));
 
   /* Update shadow for the application copy of size bytes from src to dst.
      Src and dst are application addresses. This function does not copy the
      actual application memory, it only updates shadow and origin for such
      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
 
 #endif

compiler-rt/lib/msan/msan_interceptors.cc

 DECLARE_REAL(SIZE_T, strlen, const char *s)
 DECLARE_REAL(SIZE_T, strnlen, const char *s, SIZE_T maxlen)
 DECLARE_REAL(void *, memcpy, void *dest, const void *src, uptr n)
 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; }
 };
 
 bool IsInInterceptorScope() {
   return in_interceptor_scope;
 }

compiler-rt/lib/msan/msan_interface_internal.h

 SANITIZER_INTERFACE_ATTRIBUTE
 void __sanitizer_unaligned_store64(uu64 *p, u64 x);
 
 SANITIZER_INTERFACE_ATTRIBUTE
 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

+// 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;
+}
+