linux-kernel - Re: [PATCH 06/10] x86/tdx: Mark message.str as nonstring

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Message-ID: <202502061835.F57547B@keescook>
Date: Thu, 6 Feb 2025 18:37:27 -0800
From: Kees Cook <kees@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Andy Shevchenko <andy@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	linux-coco@...ts.linux.dev,
	Sathya Prakash <sathya.prakash@...adcom.com>,
	Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
	Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>,
	Kashyap Desai <kashyap.desai@...adcom.com>,
	Sumit Saxena <sumit.saxena@...adcom.com>,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Nilesh Javali <njavali@...vell.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Sven Eckelmann <sven@...fation.org>,
	Tadeusz Struk <tadeusz.struk@...aro.org>,
	kernel test robot <lkp@...el.com>,
	Erick Archer <erick.archer@...look.com>,
	Dmitry Antipov <dmantipov@...dex.ru>,
	Ryusuke Konishi <konishi.ryusuke@...il.com>,
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
	linux-kernel@...r.kernel.org, MPT-FusionLinux.pdl@...adcom.com,
	linux-scsi@...r.kernel.org, mpi3mr-linuxdrv.pdl@...adcom.com,
	GR-QLogic-Storage-Upstream@...vell.com,
	linux-hardening@...r.kernel.org, linux-nilfs@...r.kernel.org
Subject: Re: [PATCH 06/10] x86/tdx: Mark message.str as nonstring

On Thu, Feb 06, 2025 at 05:12:11PM -0800, Dave Hansen wrote:
> On 2/6/25 17:00, Kees Cook wrote:
> > +++ b/arch/x86/coco/tdx/tdx.c
> > @@ -170,7 +170,7 @@ static void __noreturn tdx_panic(const char *msg)
> >  		/* Define register order according to the GHCI */
> >  		struct { u64 r14, r15, rbx, rdi, rsi, r8, r9, rdx; };
> >  
> > -		char str[64];
> > +		char str[64] __nonstring;
> >  	} message;
> 
> So, the patch itself makes sense. But it does end up looking kinda
> funky. We call it a "str"ing and then annotate it as not a string.

Yeah, this is true all over the place. It's a string, just not a
NUL-terminated string: *sob*

> It doesn't have to be done in this patch, but it does seem like we
> should probably not be using 'char' and also shouldn't call it anything
> close to "string". Maybe:
> 
>	 	u8 message[64] __nonstring;
> 	} message;

message.message ;)

message.chars?
message.bytes?

> In any case, feel free to carry the annotation in your tree:
> 
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>

Thanks!

-Kees

-- 
Kees Cook