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

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Date: Fri, 31 May 2024 21:34:43 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Jeff Johnson <quic_jjohnson@...cinc.com>
Cc: Kees Cook <kees@...nel.org>, Nikolay Borisov <nik.borisov@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	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 11:28:58AM -0700, Jeff Johnson wrote:
> On 5/31/2024 9:28 AM, Kees Cook wrote:
> > On Thu, May 30, 2024 at 09:23:36AM -0700, Jeff Johnson wrote:
> >> On 5/30/2024 8:42 AM, Nikolay Borisov wrote:
> >>>
> >>>
> >>> On 29.05.24 \u0433. 21:09 \u0447., 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 :)
> > 
> > Ah-ha, I see what's happening. When not built with
> > CONFIG_FORTIFY_SOURCE, fortify-string.h isn't included. But since misc.c
> > has the function definition, we get a warning that the function
> > declaration was never seen. This is likely the better solution:
> > 
> > 
> > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > index b70e4a21c15f..3f21a5e218f8 100644
> > --- a/arch/x86/boot/compressed/misc.c
> > +++ b/arch/x86/boot/compressed/misc.c
> > @@ -532,7 +532,9 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
> >  	return output + entry_offset;
> >  }
> >  
> > +#ifdef CONFIG_FORTIFY_SOURCE
> >  void __fortify_panic(const u8 reason, size_t avail, size_t size)
> >  {
> >  	error("detected buffer overflow");
> >  }
> > +#endif
> > 
> > 
> > Jeff, can you test this? (I still haven't been able to reproduce the
> > warning.)
> 
> Adding Dan since this comes during:
>   CHECK   arch/x86/boot/compressed/misc.c
> 
> What version of smatch are you using? I'm using v0.5.0-8639-gff1cc4d453ff

The "warning: symbol '__fortify_panic' was not declared. Should it be
static?" warning is from Sparse, not Smatch.  So probably that's why you
can't reproduce it.

regards,
dan carpenter