netdev - Re: [PATCH 2/3] ARM: Select ARCH_USES_CFI_GENERIC_LLVM

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Message-ID: <20251027205906.GC3183341@ax162>
Date: Mon, 27 Oct 2025 13:59:06 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, Kees Cook <kees@...nel.org>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Russell King <linux@...linux.org.uk>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Michal Kubiak <michal.kubiak@...el.com>,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH 2/3] ARM: Select ARCH_USES_CFI_GENERIC_LLVM_PASS

Hi Sami,

On Mon, Oct 27, 2025 at 08:53:49AM -0700, Sami Tolvanen wrote:
> Instead of working around issues with the generic pass, would it make
> more sense to just disable arm32 CFI with older Clang versions
> entirely? Linus, any thoughts?

That would certainly get to the heart of the problem. I have no real
strong opinion about keeping these older versions working, especially
since we have no idea how many people are actively using CONFIG_CFI on
ARM. I will say that this particular issue is rather exceptional (i.e.,
I don't know how often this would really come up in the future) because
this code is relying on the fact that these indirect calls will be made
direct by the compiler and checking for it, which does not seem like it
would be really common in the kernel otherwise. We would likely have to
forbid future use of the generic pass as well.

Cheers,
Nathan