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

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Message-ID: <202405311345.D91BF6E9@keescook>
Date: Fri, 31 May 2024 13:46:37 -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 09:08:16PM +0200, Borislav Petkov wrote:
> On Fri, May 31, 2024 at 09:53:28AM -0700, Kees Cook wrote:
> > 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.
> 
> From where I'm standing, we're not catching anything in the
> decompressor:
> 
> $  objdump -D arch/x86/boot/compressed/vmlinux | grep __fortify_panic
> 0000000001bec250 <__fortify_panic>:
> $
> 
> Sure, in vmlinux proper (allmodconfig) we do:
> 
> objdump -D vmlinux | grep __fortify_panic | wc -l
> 1417
> 
> but not in the decompressor which is special anyway.
> 
> So we can just as well disable CONFIG_FORTIFY_SOURCE in the decompressor
> and not do silly prototypes.

Please do not do this. It still benefits from compile-time sanity
checking.

-- 
Kees Cook