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Message-ID: <ae9db092-13fa-101c-1d07-5767631f7611@linux.com>
Date: Mon, 16 Jul 2018 10:24:26 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
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Subject: Re: [PATCH v14 0/6] Introduce the STACKLEAK feature and a test for it
On 16.07.2018 01:44, Ingo Molnar wrote:
>
> * Kees Cook <keescook@...omium.org> wrote:
>
>> On Thu, Jul 12, 2018 at 2:22 PM, Alexander Popov <alex.popov@...ux.com> wrote:
>>> On 12.07.2018 23:50, Ingo Molnar wrote:
>>>> Let's make sure informed users have an easy runtime way out
>>>> from the worst of the overhead that doesn't involve "recompile your distro
>>>> kernel". Also, make it easier to measure and fingerpoint the overhead...
>>>
>>> Would you like the following solution?
>>>
>>> I'll create the CONFIG_STACKLEAK_RUNTIME_DISABLE config option, which would be
>>> similar to CONFIG_SECURITY_SELINUX_DISABLE. That option will provide a sysctl
>>> switch disabling stackleak_erase(), which provides the most of performance penalty.
>>
>> I don't think CONFIG/sysctl is the way to go. I'd recommend making it
>> a boot arg and using a static key, similar to what's happening to
>> hardened_usercopy:
>
> Why no sysctl? It's a PITA to reboot systems just to turn a stupid knob off.
>
> Also, it's _much_ easier to measure performance impact when there's a sysctl.
Yes, you are right.
But I looked carefully and now see the troubles which sysctl would bring us.
Each 'task_struct' has 'lowest_stack', which must be initialized before enabling
STACKLEAK. So runtime enabling via sysctl is not plain and may bring race
conditions.
On the other hand, a boot param + static key that can only disable STACKLEAK
during __init are much more robust. I'm preparing the patch and performance
measurements.
Best regards,
Alexander
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