linux-kernel - Re: [PATCH v3 12/19] x86, kaslr: Fix a bug that relocation can not be handled when kernel is loaded above 2G

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Date:	Tue, 8 Mar 2016 13:22:51 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Vivek Goyal <vgoyal@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v3 12/19] x86, kaslr: Fix a bug that relocation can not
 be handled when kernel is loaded above 2G

On 03/07/16 at 03:30pm, Kees Cook wrote:
> On Fri, Mar 4, 2016 at 8:25 AM, Baoquan He <bhe@...hat.com> wrote:
> > When process 32 bit relocation tables a local variable 'extended'
> > is defined to calculate the physical address of relocs entry.
> > However its type is 'int' which is enough for i386, but not enough
> > for x86_64. That's why relocation can only be handled under 2G.
> > Otherwise a overflow will happen and cause system hang.
> >
> > Here change it to 'long' as 32 bit inverse relocation processing
> > does, and this change is safe for i386 relocation handling.
> >
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> 
> Acked-by: Kees Cook <keescook@...omium.org>
> 
> This patch should probably be moved up into the start of this series
> instead of living in the middle here, since it's a clear stand-alone
> bug fix.

Of course. Will put it in the start of this series. 

Thanks.

> 
> -Kees
> 
> > ---
> >  arch/x86/boot/compressed/misc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > index 4b2cd0c..70445c3 100644
> > --- a/arch/x86/boot/compressed/misc.c
> > +++ b/arch/x86/boot/compressed/misc.c
> > @@ -298,7 +298,7 @@ static void handle_relocations(void *output, unsigned long output_len)
> >          * So we work backwards from the end of the decompressed image.
> >          */
> >         for (reloc = output + output_len - sizeof(*reloc); *reloc; reloc--) {
> > -               int extended = *reloc;
> > +               long extended = *reloc;
> >                 extended += map;
> >
> >                 ptr = (unsigned long)extended;
> > --
> > 2.5.0
> >
> 
> 
> 
> -- 
> Kees Cook
> Chrome OS & Brillo Security