linux-kernel - Re: [PATCH v3 01/10] x86/cfi: Add warn option

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Message-ID: <20250219175630.GA23004@noisy.programming.kicks-ass.net>
Date: Wed, 19 Feb 2025 18:56:30 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kees Cook <kees@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, alyssa.milburn@...el.com,
	scott.d.constable@...el.com, joao@...rdrivepizza.com,
	andrew.cooper3@...rix.com, jpoimboe@...nel.org,
	jose.marchesi@...cle.com, hjl.tools@...il.com,
	ndesaulniers@...gle.com, samitolvanen@...gle.com, nathan@...nel.org,
	ojeda@...nel.org, alexei.starovoitov@...il.com, mhiramat@...nel.org,
	jmill@....edu
Subject: Re: [PATCH v3 01/10] x86/cfi: Add warn option

On Wed, Feb 19, 2025 at 09:50:54AM -0800, Kees Cook wrote:
> On Wed, Feb 19, 2025 at 05:21:08PM +0100, Peter Zijlstra wrote:
> > Rebuilding with CFI_PERMISSIVE toggled is such a pain, esp. since
> > clang is so slow.
> 
> This seems too complex; report_cfi_failure() already has the fail/warn
> logic test. I would have expected cfi_warn to take CONFIG_CFI_PERMISSIVE
> as a default instead, like:
> 
> +bool cfi_warn __ro_after_init = IS_ENABLED(CONFIG_CFI_PERMISSIVE);

In kernel/cfi.c, yes that works.

I somehow got stuck with having cfi_warn in arch/x86 and then not being
able to use it in generic code. Been too busy to debug all the fun fails
to realize I could simply stick the variable in generic code.