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

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Message-ID: <202405310951.56D9BD5C41@keescook>
Date: Fri, 31 May 2024 09:53:28 -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 Thu, May 30, 2024 at 06:46:39PM +0200, Borislav Petkov wrote:
> On May 30, 2024 6:23:36 PM GMT+02:00, Jeff Johnson <quic_jjohnson@...cinc.com> wrote:
> >On 5/30/2024 8:42 AM, Nikolay Borisov wrote:
> >> 
> >> 
> >> On 29.05.24 г. 21:09 ч., Jeff Johnson wrote:
> >>> As discussed in [1] add a prototype for __fortify_panic() to fix the
> >>> 'make W=1 C=1' warning:
> >>>
> >>> arch/x86/boot/compressed/misc.c:535:6: warning: symbol '__fortify_panic' was not declared. Should it be static?
> >> 
> >> Actually doesn't it make sense to have this defined under ../string.h ? 
> >> Actually given that we don't have any string fortification under the 
> >> boot/  why have the fortify _* functions at all ?
> >
> >I'll let Kees answer these questions since I just took guidance from him :)
> 
> The more important question is how does the decompressor build even know of this symbol? And then make it forget it again instead of adding silly prototypes...

Under CONFIG_FORTIFY_SOURCE, the boot code *does* still uses
fortify-string.h. It lets us both catch mistakes we can discover at
compile and will catch egregious runtime mistakes, though the reporting
is much simpler in the boot code.

-- 
Kees Cook