Re: [PATCH] ASLRv3: randomize_va_space=3 preventing offset2lib attack

[Kees Cook]

On Mon, Dec 8, 2014 at 12:09 PM, Christian Borntraeger
<borntraeger@xxxxxxxxxx> wrote:
> Am 05.12.2014 um 01:07 schrieb Hector Marco:
>> [PATCH] ASLRv3: randomize_va_space=3 preventing offset2lib attack
>>
>>   The issue appears on PIE linked executables when all memory areas of
>>   a process are randomized (randomize_va_space=2). In this case, the
>>   attack "offset2lib" de-randomizes all library areas on 64 bit Linux
>>   systems in less than one second.
>>
>>   Further details of the PoC attack at:
>>   http://cybersecurity.upv.es/attacks/offset2lib/offset2lib.html
>>
>>   PIE linked applications are loaded side by side with the dynamic
>>   libraries, which is exploited by the offset2lib attack. Moving away
>>   the executable from the mmap_base area (libraries area) prevents the
>>   attack.
>>
>>   This patch loads the PIE linked executable in a different area than
>>   the libraries when randomize_va_space=3.
>>
>>   Patch implementation details:
>>
>>    - The ELF_ET_DYN_BASE address is used as the base to load randomly
>>      the PIE executable.
>>
>>    - The executable image has the same entropy than
>>      randomize_va_space=2.
> [...]
>> --- a/arch/arm/mm/mmap.c
>> +++ b/arch/arm/mm/mmap.c
> [...]
>> --- a/arch/arm64/mm/mmap.c
>> +++ b/arch/arm64/mm/mmap.c
> [...]
>
>> --- a/arch/x86/mm/mmap.c
>> +++ b/arch/x86/mm/mmap.c
> [...]
>
> FWIW, please note that s390 and power (maybe others?) also have PIE support done differently, e.g.
> commit d2c9dfccbc3 ("[S390] Randomize PIEs") and commit 501cb16d3cfdc ("powerpc: Randomise PIEs")
>
> What I can tell from a quick look both architectures should be fine regarding offsetlib, as they place the executable already in a different section and randomize those differently even with randomize_va_space=2.
>
> Would it make sense to unify the implementations again?

Seems like that would be best. If this is already being done on
non-x86 and non-arm, we should just fix x86 and arm to DTRT. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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