linux-kernel - Re: Additional info on modpost segfault

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Message-ID: <4C129FC7.8070308@zytor.com>
Date:	Fri, 11 Jun 2010 13:42:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Krzysztof Halasa <khc@...waw.pl>
CC:	Alan <alan@...eserver.org>, Michal Marek <mmarek@...e.cz>,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Additional info on modpost segfault

Michal, are you sending this to Linus?

	-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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