linux-kernel - Re: [PATCH] x86/boot: add prototype for __fortify

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Message-ID: <202405311431.BF9FE3F7A7@keescook>
Date: Fri, 31 May 2024 14:34:07 -0700
From: Kees Cook <kees@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Jeff Johnson <quic_jjohnson@...cinc.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] x86/boot: add prototype for __fortify_panic()

On Fri, May 31, 2024 at 11:20:09PM +0200, Borislav Petkov wrote:
> So I get an allergic reaction everytime we wag the dog - i.e., fix the
> code because some tool or option can't handle it even if it is
> a perfectly fine code. In that case it is an unused symbol.
> 
> And frankly, I'd prefer the silly warning to denote that fortify doesn't
> need to do any checking there vs shutting it up just because.

If we want to declare that x86 boot will never perform string handling
on strings with unknown lengths, we could just delete the boot/
implementation of __fortify_panic(), and make it a hard failure if such
cases are introduced in the future. This hasn't been a particularly
friendly solution in the past, though, as the fortify routines do tend
to grow additional coverage over time, so there may be future cases that
do trip the runtime checking...

-- 
Kees Cook