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Date:   Mon, 5 Mar 2018 21:25:35 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Laura Abbott <labbott@redhat.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Alexander Popov <alex.popov@linux.com>,
        kernel-hardening@lists.openwall.com,
        Kees Cook <keescook@chromium.org>,
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        Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Tycho Andersen <tycho@tycho.ws>,
        Mark Rutland <mark.rutland@arm.com>,
        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>,
        "Dmitry V . Levin" <ldv@altlinux.org>,
        Emese Revfy <re.emese@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
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        Masami Hiramatsu <mhiramat@kernel.org>,
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        Al Viro <viro@zeniv.linux.org.uk>,
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        Vikas Shivappa <vikas.shivappa@linux.intel.com>,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC v9 2/7] x86/entry: Add STACKLEAK erasing the kernel
 stack at the end of syscalls
Message-ID: <20180305202535.GX25201@hirez.programming.kicks-ass.net>
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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.