From cea84ab93aeb079a358ab1c8aeba6d9140ef8b47 Mon Sep 17 00:00:00 2001 From: Julian Lettner Date: Thu, 24 Jan 2019 01:06:19 +0000 Subject: [Sanitizers] UBSan unreachable incompatible with ASan in the presence of `noreturn` calls Summary: UBSan wants to detect when unreachable code is actually reached, so it adds instrumentation before every `unreachable` instruction. However, the optimizer will remove code after calls to functions marked with `noreturn`. To avoid this UBSan removes `noreturn` from both the call instruction as well as from the function itself. Unfortunately, ASan relies on this annotation to unpoison the stack by inserting calls to `_asan_handle_no_return` before `noreturn` functions. This is important for functions that do not return but access the the stack memory, e.g., unwinder functions *like* `longjmp` (`longjmp` itself is actually "double-proofed" via its interceptor). The result is that when ASan and UBSan are combined, the `noreturn` attributes are missing and ASan cannot unpoison the stack, so it has false positives when stack unwinding is used. Changes: # UBSan now adds the `expect_noreturn` attribute whenever it removes the `noreturn` attribute from a function # ASan additionally checks for the presence of this attribute Generated code: ``` call void @__asan_handle_no_return // Additionally inserted to avoid false positives call void @longjmp call void @__asan_handle_no_return call void @__ubsan_handle_builtin_unreachable unreachable ``` The second call to `__asan_handle_no_return` is redundant. This will be cleaned up in a follow-up patch. rdar://problem/40723397 Reviewers: delcypher, eugenis Tags: #sanitizers Differential Revision: https://reviews.llvm.org/D56624 llvm-svn: 352003 --- llvm/lib/IR/Attributes.cpp | 2 ++ 1 file changed, 2 insertions(+) (limited to 'llvm/lib/IR/Attributes.cpp') diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp index a474d5740fe..ab49adba81c 100644 --- a/llvm/lib/IR/Attributes.cpp +++ b/llvm/lib/IR/Attributes.cpp @@ -298,6 +298,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const { return "noredzone"; if (hasAttribute(Attribute::NoReturn)) return "noreturn"; + if (hasAttribute(Attribute::ExpectNoReturn)) + return "expect_noreturn"; if (hasAttribute(Attribute::NoCfCheck)) return "nocf_check"; if (hasAttribute(Attribute::NoRecurse)) -- cgit v1.2.3