lkml.org 
[lkml]   [2017]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: x86/module: Detect corrupt relocations against nonzero data
+++ Josh Poimboeuf [02/11/17 21:19 -0500]:
>On Thu, Nov 02, 2017 at 04:57:11PM -0500, Josh Poimboeuf wrote:
>> There have been some cases where external tooling (e.g., kpatch-build)
>> creates a corrupt relocation which targets the wrong address. This is a
>> silent failure which can corrupt memory in unexpected places.
>>
>> On x86, the bytes of data being overwritten by relocations are always
>> initialized to zero beforehand. Use that knowledge to add sanity checks
>> to detect such cases before they corrupt memory.
>>
>> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
>> ---
>> arch/x86/kernel/module.c | 13 +++++++++++++
>> 1 file changed, 13 insertions(+)
>>
>> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
>> index 62e7d70aadd5..a69b12617820 100644
>> --- a/arch/x86/kernel/module.c
>> +++ b/arch/x86/kernel/module.c
>> @@ -172,19 +172,27 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>> case R_X86_64_NONE:
>> break;
>> case R_X86_64_64:
>> + if (*(u64 *)loc != 0)
>> + goto nonzero;
>> *(u64 *)loc = val;
>> break;
>> case R_X86_64_32:
>> + if (*(u32 *)loc != 0)
>> + goto nonzero;
>> *(u32 *)loc = val;
>> if (val != *(u32 *)loc)
>> goto overflow;
>> break;
>> case R_X86_64_32S:
>> + if (*(s32 *)loc != 0)
>> + goto nonzero;
>> *(s32 *)loc = val;
>> if ((s64)val != *(s32 *)loc)
>> goto overflow;
>> break;
>> case R_X86_64_PC32:
>> + if (*(u64 *)loc != 0)
>> + goto nonzero;
>> val -= (u64)loc;
>> *(u32 *)loc = val;
>
>NACK - this last bit is obviously a bug, not sure how it passed my
>testing without module load failures...

Thanks for the patch Josh, btw - could you also CC the x86 folks when
you send out v2?

Thanks!

Jessica

\
 
 \ /
  Last update: 2017-11-03 11:23    [W:0.029 / U:0.484 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site