From 040c211bc41bcea76ca9e186af298567976b9d84 Mon Sep 17 00:00:00 2001 From: Kostya Kortchinsky Date: Mon, 11 Sep 2017 19:59:40 +0000 Subject: [scudo] Fix improper TSD init after TLS destructors are called Summary: Some of glibc's own thread local data is destroyed after a user's thread local destructors are called, via __libc_thread_freeres. This might involve calling free, as is the case for strerror_thread_freeres. If there is no prior heap operation in the thread, this free would end up initializing some thread specific data that would never be destroyed properly (as user's pthread destructors have already been called), while still being deallocated when the TLS goes away. As a result, a program could SEGV, usually in __sanitizer::AllocatorGlobalStats::Unregister, where one of the doubly linked list links would refer to a now unmapped memory area. To prevent this from happening, we will not do a full initialization from the deallocation path. This means that the fallback cache & quarantine will be used if no other heap operation has been called, and we effectively prevent the TSD being initialized and never destroyed. The TSD will be fully initialized for all other paths. In the event of a thread doing only frees and nothing else, a TSD would never be initialized for that thread, but this situation is unlikely and we can live with that. Reviewers: alekseyshl Reviewed By: alekseyshl Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D37697 llvm-svn: 312939 --- compiler-rt/lib/scudo/scudo_allocator.cpp | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'compiler-rt/lib/scudo/scudo_allocator.cpp') diff --git a/compiler-rt/lib/scudo/scudo_allocator.cpp b/compiler-rt/lib/scudo/scudo_allocator.cpp index 4f87d35232d..92155797ca4 100644 --- a/compiler-rt/lib/scudo/scudo_allocator.cpp +++ b/compiler-rt/lib/scudo/scudo_allocator.cpp @@ -495,7 +495,13 @@ struct ScudoAllocator { // Deallocates a Chunk, which means adding it to the delayed free list (or // Quarantine). void deallocate(void *UserPtr, uptr DeleteSize, AllocType Type) { - initThreadMaybe(); + // For a deallocation, we only ensure minimal initialization, meaning thread + // local data will be left uninitialized for now (when using ELF TLS). The + // fallback cache will be used instead. This is a workaround for a situation + // where the only heap operation performed in a thread would be a free past + // 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(UserPtr); if (UNLIKELY(!UserPtr)) return; -- cgit v1.2.3