linux-kernel - Re: Additional info on modpost segfault

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Date:	Sat, 12 Jun 2010 00:49:47 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Krzysztof Halasa <khc@...waw.pl>, Alan <alan@...eserver.org>,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Additional info on modpost segfault

On Fri, Jun 11, 2010 at 01:42:47PM -0700, H. Peter Anvin wrote:
> Michal, are you sending this to Linus?

I'll, once Linus takes another pull request I sent a couple of hours
ago. Thanks for the patch Krzysztof!

Michal

> 
> 	-hpa
> 
> 
> On 06/10/2010 04:08 PM, Krzysztof Halasa wrote:
> > Alan <alan@...eserver.org> writes:
> > 
> >> program: /home/alan/GitTrees/linux-2.6-mid-ref/scripts/mod/modpost -o
> >> Module.symvers -S vmlinux.o
> >>
> >> Program received signal SIGSEGV, Segmentation fault.
> > 
> > It just hit me.
> > It's the offset calculation in reloc_location() which overflows:
> >         return (void *)elf->hdr + sechdrs[section].sh_offset +
> >                (r->r_offset - sechdrs[section].sh_addr);
> > 
> > E.g. for the first rodata r entry:
> > r->r_offset < sechdrs[section].sh_addr
> > and the expression in the parenthesis produces 0xFFFFFFE0 or something
> > equally wise.
> > 
> > Does the attached patch fix it?
> > 
> > Signed-off-by: Krzysztof Hałasa <khc@...waw.pl>
> > 
> > --- a/scripts/mod/modpost.c
> > +++ b/scripts/mod/modpost.c
> > @@ -1317,8 +1317,8 @@ static unsigned int *reloc_location(struct elf_info *elf,
> >  	Elf_Shdr *sechdrs = elf->sechdrs;
> >  	int section = sechdr->sh_info;
> >  
> >  	return (void *)elf->hdr + sechdrs[section].sh_offset +
> > -		(r->r_offset - sechdrs[section].sh_addr);
> > +		r->r_offset - sechdrs[section].sh_addr;
> >  }
> >  
> >  static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
> > --
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