From b7926ce6d7a83cdf70c68d82bc3389c04009b841 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Fri, 23 Oct 2020 11:41:17 -0700 Subject: [IR] add fn attr for no_stack_protector; prevent inlining on mismatch It's currently ambiguous in IR whether the source language explicitly did not want a stack a stack protector (in C, via function attribute no_stack_protector) or doesn't care for any given function. It's common for code that manipulates the stack via inline assembly or that has to set up its own stack canary (such as the Linux kernel) would like to avoid stack protectors in certain functions. In this case, we've been bitten by numerous bugs where a callee with a stack protector is inlined into an __attribute__((__no_stack_protector__)) caller, which generally breaks the caller's assumptions about not having a stack protector. LTO exacerbates the issue. While developers can avoid this by putting all no_stack_protector functions in one translation unit together and compiling those with -fno-stack-protector, it's generally not very ergonomic or as ergonomic as a function attribute, and still doesn't work for LTO. See also: https://lore.kernel.org/linux-pm/20200915172658.1432732-1-rkir@google.com/ https://lore.kernel.org/lkml/20200918201436.2932360-30-samitolvanen@google.com/T/#u Typically, when inlining a callee into a caller, the caller will be upgraded in its level of stack protection (see adjustCallerSSPLevel()). By adding an explicit attribute in the IR when the function attribute is used in the source language, we can now identify such cases and prevent inlining. Block inlining when the callee and caller differ in the case that one contains `nossp` when the other has `ssp`, `sspstrong`, or `sspreq`. Fixes pr/47479. Reviewed By: void Differential Revision: https://reviews.llvm.org/D87956 --- clang/lib/CodeGen/CodeGenModule.cpp | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) (limited to 'clang/lib/CodeGen/CodeGenModule.cpp') diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp index 8b53ec9ab4a9..809e877e42aa 100644 --- a/clang/lib/CodeGen/CodeGenModule.cpp +++ b/clang/lib/CodeGen/CodeGenModule.cpp @@ -1594,14 +1594,14 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D, if (!hasUnwindExceptions(LangOpts)) B.addAttribute(llvm::Attribute::NoUnwind); - if (!D || !D->hasAttr()) { - if (LangOpts.getStackProtector() == LangOptions::SSPOn) - B.addAttribute(llvm::Attribute::StackProtect); - else if (LangOpts.getStackProtector() == LangOptions::SSPStrong) - B.addAttribute(llvm::Attribute::StackProtectStrong); - else if (LangOpts.getStackProtector() == LangOptions::SSPReq) - B.addAttribute(llvm::Attribute::StackProtectReq); - } + if (D && D->hasAttr()) + B.addAttribute(llvm::Attribute::NoStackProtect); + else if (LangOpts.getStackProtector() == LangOptions::SSPOn) + B.addAttribute(llvm::Attribute::StackProtect); + else if (LangOpts.getStackProtector() == LangOptions::SSPStrong) + B.addAttribute(llvm::Attribute::StackProtectStrong); + else if (LangOpts.getStackProtector() == LangOptions::SSPReq) + B.addAttribute(llvm::Attribute::StackProtectReq); if (!D) { // If we don't have a declaration to control inlining, the function isn't -- cgit v1.2.3