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Date: Mon, 31 Jan 2022 13:13:30 -0800 From: Kees Cook <keescook@...omium.org> To: Nick Desaulniers <ndesaulniers@...gle.com> Cc: Nathan Chancellor <nathan@...nel.org>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [PATCH v4] fortify: Work around Clang inlining bugs On Mon, Jan 31, 2022 at 11:04:36AM -0800, Nick Desaulniers wrote: > On Sun, Jan 30, 2022 at 10:22 AM Kees Cook <keescook@...omium.org> wrote: > > > > To enable FORTIFY_SOURCE support for Clang, the kernel must work around > > a pair of bugs, related to Clang's inlining: > > > > 1) Change all the fortified string APIs into macros with different > > inline names to bypass Clang's broken inline-of-a-builtin detection: > > https://bugs.llvm.org/show_bug.cgi?id=50322 > > > > 2) Lift all misbehaving __builtin_object_size() calls into the macros > > to bypass Clang's broken __builtin_object_size() arguments-of-an-inline > > visibility: > > https://github.com/ClangBuiltLinux/linux/issues/1401 > > ^ mentions a difference in compilers for mode 1. I wonder if this > patch could "hoist" the BOS calls into the macro ONLY for mode 1 and > not mode 0 usage? i.e. the str* functions, not the mem* functions. Everything (with a couple exceptions) is using mode 1 after the earlier patches in the series. e.g.: +#define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ + __builtin_object_size(p, 0), __builtin_object_size(q, 0), \ + __builtin_object_size(p, 1), __builtin_object_size(q, 1), \ + memcpy) > It's too late to fix these in clang-13. If we get a fix in clang-14 > or later, what does that look like for this header? Is there a way we If the bos mode 1 got fixed for Clang 14, this patch would likely be dropped and the Clang + FORTIFY version check would be moved to Clang 14. > can provide a different header than include/linux/fortify-string.h > just for clang-13 (or whatever versions until the above are fixed)? So much of it would be identical. This macro-ification is least invasive, and it's pretty invasive. > I don't see this series getting backported to stable, where older > versions of clang may still be in use. Right. > I'm tempted to say "let's get get these 2 fixed in clang-14" but we'll > probably have to trade something off the existing TODO list. Agreed. -- Kees Cook
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