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Message-ID: <b6abd009-8f64-c5a2-6496-6affb31ad75e@linux.com>
Date: Tue, 6 Mar 2018 00:21:02 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Peter Zijlstra <peterz@...radead.org>, Laura Abbott <labbott@...hat.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>,
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x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v9 2/7] x86/entry: Add STACKLEAK erasing the kernel
stack at the end of syscalls
On 05.03.2018 23:25, Peter Zijlstra wrote:
> On Mon, Mar 05, 2018 at 11:43:19AM -0800, Laura Abbott wrote:
>> On 03/05/2018 08:41 AM, Dave Hansen wrote:
>>> On 03/03/2018 12:00 PM, Alexander Popov wrote:
>>>> Documentation/x86/x86_64/mm.txt | 2 +
>>>> arch/Kconfig | 27 ++++++++++
>>>> arch/x86/Kconfig | 1 +
>>>> arch/x86/entry/entry_32.S | 88 +++++++++++++++++++++++++++++++
>>>> arch/x86/entry/entry_64.S | 108 +++++++++++++++++++++++++++++++++++++++
>>>> arch/x86/entry/entry_64_compat.S | 11 ++++
>>>
>>> This is a *lot* of assembly. I wonder if you tried at all to get more
>>> of this into C or whether you just inherited the assembly from the
>>> original code?
>>>
>>
>> This came up previously http://www.openwall.com/lists/kernel-hardening/2017/10/23/5
>> there were concerns about trusting C to do the right thing as well as
>> speed.
>
> And therefore the answer to this obvious question should've been part of
> the Changelog :-)
>
> Dave is last in a long line of people asking this same question.
Yes, actually the changelog in the cover letter contains that:
After some experiments, kept the asm implementation of erase_kstack(),
because it gives a full control over the stack for clearing it neatly
and doesn't offend KASAN.
Moreover, later erase_kstack() on x86_64 became different from one on x86_32.
Best regards,
Alexander
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