linux-kernel - Re: + binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patch added to -mm tree

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Message-ID: <CAGXu5j+fLM4YV==xjTsS4qU+CZY_ohL2cdAcEcXBjmS2WHa6Sw@mail.gmail.com>
Date:	Tue, 6 Nov 2012 20:29:33 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Jeff Liu <jeff.liu@...cle.com>
Cc:	akpm@...ux-foundation.org, aedilger@...il.com,
	alan@...ux.intel.com, arnn@...db.de, gregkh@...uxfoundation.org,
	jakub@...hat.com, james.l.morris@...cle.com,
	john.sobecki@...cle.com, tytso@....edu, viro@...iv.linux.org.uk,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: + binfmt_elfc-use-get_random_int-to-fix-entropy-depleting.patch
 added to -mm tree

On Tue, Nov 6, 2012 at 8:21 PM, Jeff Liu <jeff.liu@...cle.com> 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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