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References: <20211209221545.2333249-1-pcc@google.com> <fce9898e392f42a0830892a1735deb3e@AcuMS.aculab.com>
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From:   Peter Collingbourne <pcc@google.com>
Date:   Mon, 13 Dec 2021 11:48:35 -0800
Message-ID: <CAMn1gO5mBHR3-Wd2CyxQ8PYt8apTiWNOtFwKY4duwXvGwkZFWA@mail.gmail.com>
Subject: Re: [PATCH v4 0/7] kernel: introduce uaccess logging
To:     David Laight <David.Laight@aculab.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        YiFei Zhu <yifeifz2@illinois.edu>,
        Mark Rutland <mark.rutland@arm.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        Chris Hyser <chris.hyser@oracle.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Dmitry Vyukov <dvyukov@google.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Alexey Gladkov <legion@kernel.org>,
        Ran Xiaokai <ran.xiaokai@zte.com.cn>,
        David Hildenbrand <david@redhat.com>,
        Xiaofeng Cao <caoxiaofeng@yulong.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Thomas Cedeno <thomascedeno@google.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Evgenii Stepanov <eugenis@google.com>
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On Sat, Dec 11, 2021 at 9:23 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Peter Collingbourne
> > Sent: 09 December 2021 22:16
> >
> > This patch series introduces a kernel feature known as uaccess
> > logging, which allows userspace programs to be made aware of the
> > address and size of uaccesses performed by the kernel during
> > the servicing of a syscall. More details on the motivation
> > for and interface to this feature are available in the file
> > Documentation/admin-guide/uaccess-logging.rst added by the final
> > patch in the series.
>
> How does this work when get_user() and put_user() are used to
> do optimised copies?
>
> While adding checks to copy_to/from_user() is going to have
> a measurable performance impact - even if nothing is done,
> adding them to get/put_user() (and friends) is going to
> make some hot paths really slow.
>
> So maybe you could add it so KASAN test kernels, but you can't
> sensibly enable it on a production kernel.
>
> Now, it might be that you could semi-sensibly log 'data' transfers.
> But have you actually looked at all the transfers that happen
> for something like sendmsg().
> The 'user copy hardening' code already has a significant impact
> on that code (in many places).

Hi David,

Yes, I realised after I sent out my patch (and while writing test
cases for it) that it didn't cover get_user()/put_user(). I have a
patch under development that will add this coverage. I used it to run
my invalid syscall and uname benchmarks and the results were basically
the same as without the coverage.

Are you aware of any benchmarks that cover sendmsg()? I can try to
look at writing my own if not. I was also planning to write a
benchmark that uses getresuid() as this was the simplest syscall that
I could find that does multiple put_user() calls.

Peter