[msan] Don't unpoison phdrs on dlopen(NULL, 0)

Summary:
dlopen(NULL, ...) is intended to give you back a handle to the
executable for use with dlsym. Casting it to link_map and using it with
ForEachMappedRegion results in a crash.

We also shouldn't unpoison the globals of a DSO that is already in
memory. This ensures that we don't do it for the executable, but in
general, MSan may have false negatives if the DSO is already loaded.

Reviewers: eugenis

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14795

llvm-svn: 253530

2 files changed, 22 insertions, 4 deletions

diff --git a/compiler-rt/lib/msan/msan_interceptors.cc b/compiler-rt/lib/msan/msan_interceptors.cc
index 1bf196ecdbe..fc28e080f26 100644
--- a/compiler-rt/lib/msan/msan_interceptors.cc
+++ b/compiler-rt/lib/msan/msan_interceptors.cc
@@ -1434,10 +1434,11 @@ int OnExit() {
   } while (false)  // FIXME
 #define COMMON_INTERCEPTOR_BLOCK_REAL(name) REAL(name)
 #define COMMON_INTERCEPTOR_ON_EXIT(ctx) OnExit()
-#define COMMON_INTERCEPTOR_LIBRARY_LOADED(filename, handle)  \
-  do {                                                       \
-    link_map *map = GET_LINK_MAP_BY_DLOPEN_HANDLE((handle)); \
-    if (map) ForEachMappedRegion(map, __msan_unpoison);      \
+#define COMMON_INTERCEPTOR_LIBRARY_LOADED(filename, handle)                    \
+  do {                                                                         \
+    link_map *map = GET_LINK_MAP_BY_DLOPEN_HANDLE((handle));                   \
+    if (filename && map)                                                       \
+      ForEachMappedRegion(map, __msan_unpoison);                               \
   } while (false)
 
 #define COMMON_INTERCEPTOR_GET_TLS_RANGE(begin, end)                           \
diff --git a/compiler-rt/test/msan/dlopen_executable.cc b/compiler-rt/test/msan/dlopen_executable.cc
new file mode 100644
index 00000000000..ac8a14b9407
--- /dev/null
+++ b/compiler-rt/test/msan/dlopen_executable.cc
@@ -0,0 +1,17 @@
+// RUN: %clangxx_msan -O0 %s -o %t && not %run %t 2>&1 | FileCheck %s
+
+#include <assert.h>
+#include <dlfcn.h>
+#include <stdlib.h>
+
+static int my_global;
+
+int main(void) {
+  int *uninit = (int*)malloc(sizeof(int));
+  my_global = *uninit;
+  void *p = dlopen(0, RTLD_NOW);
+  assert(p && "failed to get handle to executable");
+  return my_global;
+  // CHECK: MemorySanitizer: use-of-uninitialized-value
+  // CHECK: #0 {{.*}} in main{{.*}}dlopen_executable.cc:[[@LINE-2]]
+}