[scudo] Allow for weak hooks, gated by a define

Summary:
Hooks in the allocation & deallocation paths can be a security risk (see for an
example https://scarybeastsecurity.blogspot.com/2016/11/0day-exploit-advancing-exploitation.html
which used the glibc's __free_hook to complete exploitation).

But some users have expressed a need for them, even if only for tests and
memory benchmarks. So allow for `__sanitizer_malloc_hook` &
`__sanitizer_free_hook` to be called if defined, and gate them behind a global
define `SCUDO_CAN_USE_HOOKS` defaulting to 0.

Reviewers: alekseyshl

Reviewed By: alekseyshl

Subscribers: #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D42430

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@323278 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/scudo/scudo_allocator.cpp b/lib/scudo/scudo_allocator.cpp
index 0e18141f4..31317b7cf 100644
--- a/lib/scudo/scudo_allocator.cpp
+++ b/lib/scudo/scudo_allocator.cpp
@@ -430,7 +430,8 @@ struct ScudoAllocator {
     }
     void *Ptr = reinterpret_cast<void *>(UserPtr);
     Chunk::storeHeader(Ptr, &Header);
-    // if (&__sanitizer_malloc_hook) __sanitizer_malloc_hook(Ptr, Size);
+    if (SCUDO_CAN_USE_HOOKS && &__sanitizer_malloc_hook)
+      __sanitizer_malloc_hook(Ptr, Size);
     return Ptr;
   }
 
@@ -480,7 +481,8 @@ struct ScudoAllocator {
     // the TLS destructors, ending up in initialized thread specific data never
     // being destroyed properly. Any other heap operation will do a full init.
     initThreadMaybe(/*MinimalInit=*/true);
-    // if (&__sanitizer_free_hook) __sanitizer_free_hook(Ptr);
+    if (SCUDO_CAN_USE_HOOKS && &__sanitizer_free_hook)
+      __sanitizer_free_hook(Ptr);
     if (UNLIKELY(!Ptr))
       return;
     if (UNLIKELY(!Chunk::isAligned(Ptr))) {