Re: + binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patchadded to -mm tree

[Kees Cook]

On Tue, Nov 6, 2012 at 8:21 PM, Jeff Liu <jeff.liu@xxxxxxxxxx> wrote:
> Hi Andrew and Kees,
>
> Great thanks for both your comments!
>
> On 11/07/2012 09:11 AM, Kees Cook wrote:
>> Hrm, I don't like this. get_random_int() specifically says: "Get a
>> random word for internal kernel use only." The intent of AT_RANDOM is
>> for userspace pRNG seeding (though glibc currently uses it directly
>> for stack protector and pointer mangling), which is not "internal
>> kernel use only". :) Though I suppose this is already being used for
>> the randomize_stack_top(), but I think it'd still be better to use
>> higher quality bits.
> Btw Kees, does it sounds make sense if we just return the 16 bytes
> uninitialized stack array if the user disable the stack randomize via
> "/proc/sys/kernel/randomize_va_space = 0" or via the related sysctl, or
> even specified norandmaps on boot?

No, I feel that ASLR (randomize_va_space) is distinctly separate from
how glibc uses AT_RANDOM (stack protector and pointer mangling).
AT_RANDOM should remain active even if randomize_va_space is 0.

-Kees

-- 
Kees Cook
Chrome OS Security
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