linux-hardening - Re: [PATCH v4] fortify: Work around Clang inlining bugs

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Date:   Mon, 31 Jan 2022 11:04:36 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
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 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.

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
can provide a different header than include/linux/fortify-string.h
just for clang-13 (or whatever versions until the above are fixed)?

I don't see this series getting backported to stable, where older
versions of clang may still be in use.

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.
-- 
Thanks,
~Nick Desaulniers