linux-hardening - Re: [PATCH v2] x86/stackprotector: Work around strict Clang TLS symbol requirements

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Message-ID: <CAMj1kXF7aFyBOOxQQsvsAsnvo3FYrkU=KA1BiMeSuKq1KHC1qA@mail.gmail.com>
Date: Tue, 15 Oct 2024 12:56:57 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, x86@...nel.org, llvm@...ts.linux.dev, 
	linux-hardening@...r.kernel.org, stable@...r.kernel.org, 
	Fangrui Song <i@...kray.me>, Brian Gerst <brgerst@...il.com>, Uros Bizjak <ubizjak@...il.com>, 
	Nathan Chancellor <nathan@...nel.org>, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2] x86/stackprotector: Work around strict Clang TLS
 symbol requirements

On Mon, 14 Oct 2024 at 22:59, Kees Cook <kees@...nel.org> wrote:
>
> On Wed, Oct 09, 2024 at 02:43:53PM +0200, Ard Biesheuvel wrote:
> > However, if a non-TLS definition of the symbol in question is visible in
> > the same compilation unit (which amounts to the whole of vmlinux if LTO
> > is enabled), it will drop the per-CPU prefix and emit a load from a
> > bogus address.
>
> I take this to mean that x86 32-bit kernels built with the stack
> protector and using Clang LTO will crash very quickly?
>

Yeah. The linked issue is not quite clear, but it does suggest things
are pretty broken in that case.