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Subject: Re: [PATCH RFC v9 2/7] x86/entry: Add STACKLEAK erasing the kernel
 stack at the end of syscalls
To: Laura Abbott <labbott@redhat.com>, Alexander Popov
 <alex.popov@linux.com>, kernel-hardening@lists.openwall.com,
 Kees Cook <keescook@chromium.org>, PaX Team <pageexec@freemail.hu>,
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 Ard Biesheuvel <ard.biesheuvel@linaro.org>, Borislav Petkov <bp@alien8.de>,
 Richard Sandiford <richard.sandiford@arm.com>,
 Thomas Gleixner <tglx@linutronix.de>, "H . Peter Anvin" <hpa@zytor.com>,
 Peter Zijlstra <a.p.zijlstra@chello.nl>, "Dmitry V . Levin"
 <ldv@altlinux.org>, Emese Revfy <re.emese@gmail.com>,
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 "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
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 Andrew Morton <akpm@linux-foundation.org>,
 Alexei Starovoitov <ast@kernel.org>, Josef Bacik <jbacik@fb.com>,
 Masami Hiramatsu <mhiramat@kernel.org>, Nicholas Piggin <npiggin@gmail.com>,
 Al Viro <viro@zeniv.linux.org.uk>, "David S . Miller" <davem@davemloft.net>,
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References: <1520107232-14111-1-git-send-email-alex.popov@linux.com>
 <1520107232-14111-3-git-send-email-alex.popov@linux.com>
 <d968e58a-3abd-8e3c-cee3-00c19c1b6430@linux.intel.com>
 <94f268b2-31a4-620a-86ed-325d5bb33c57@redhat.com>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <da695ba4-57d1-4a77-a96c-ad38ea370cdc@linux.intel.com>
Date: Mon, 5 Mar 2018 11:50:54 -0800
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On 03/05/2018 11:43 AM, 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.

I'm really just curious if anyone tried it and what tradeoffs were made.