From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754650Ab0LJIJZ (ORCPT ); Fri, 10 Dec 2010 03:09:25 -0500 Received: from mail.lixom.net ([70.86.134.90]:49818 "EHLO mail.lixom.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754579Ab0LJIJX (ORCPT ); Fri, 10 Dec 2010 03:09:23 -0500 Date: Fri, 10 Dec 2010 02:09:23 -0600 From: Olof Johansson To: Michal Marek Cc: Rusty Russell , Sam Ravnborg , Andrew Morton , linux-kernel@vger.kernel.org, raymes@google.com Subject: [PATCH] modpost: Fix address calculation in reloc_location() Message-ID: <20101210080923.GA13474@lixom.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch fixes a segfault in modpost that is observed when the gold linker is used to link the input objects. The problem is that reloc_location (modpost.c) is computing the address of the relocation target incorrectly. Here, elf->hdr points to the beginning of the ELF file in memory, sechdr points to the relocation section header, section is the index of the section being relocated, and sechdrs[section].sh_offset would be the offset of that section, relative to the beginning of the ELF file. Adding elf->hdr + sechdrs[section].sh_offset gives you the address of the beginning of the section, and adding r->r_offset to that gives you the address of the location to be relocated. You do not need to subtract sechdrs[section].sh_addr from that -- the result of this is an address outside the file, and causes the segfault when addend_386_rel tries to dereference it. This bug is not observed when GNU ld is used to link the inputs. The object file ubuntu/omnibook/omnibook.o is the result of an ld -r of several other files. When GNU ld does an ld -r, it sets the vaddr field for each section to 0, but gold lays out the section addresses sequentially instead: Section Headers: [Nr] Name Type Addr Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .text PROGBITS 00000000 000034 004794 00 AX 0 0 4 [ 2] .data PROGBITS 0000b9d0 0047c8 0009c0 00 WA 0 0 4 [ 3] .bss NOBITS 000162f8 005188 00013c 00 WA 0 0 4 [ 4] .rodata.str1.1 PROGBITS 00004f2d 0052c4 001b1a 01 AMS 0 0 1 [ 5] .init.text PROGBITS 00004794 006dde 0005fa 00 AX 0 0 1 [ 6] .exit.text PROGBITS 00004d8e 0073d8 00018a 00 AX 0 0 1 ... So the bug in the tool remained undiscovered because the section's vaddr always happened to be 0. Signed-off-by: Raymes Khoury Signed-off-by: Olof Johansson --- scripts/mod/modpost.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 1ec7158..623bffc 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -1438,7 +1438,7 @@ static unsigned int *reloc_location(struct elf_info *elf, int section = shndx2secindex(sechdr->sh_info); return (void *)elf->hdr + sechdrs[section].sh_offset + - r->r_offset - sechdrs[section].sh_addr; + r->r_offset; } static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)