linux-kernel - Re: Additional info on modpost segfault

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Date:	Thu, 10 Jun 2010 17:06:34 -0700 (PDT)
From:	alan <alan@...eserver.org>
To:	Krzysztof Halasa <khc@...waw.pl>
cc:	Michal Marek <mmarek@...e.cz>,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Additional info on modpost segfault

On Fri, 11 Jun 2010, 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?

YES!

Thank you!

Now the big question is why does this compile on older versions of gcc?

This needs to get added into 2.6.35-rc2.


>
> Signed-off-by: Krzysztof Haÿÿasa <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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