linux-kernel - Re: [PATCH v4 0/7] kernel: introduce uaccess logging

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Date:   Mon, 13 Dec 2021 11:48:35 -0800
From:   Peter Collingbourne <pcc@...gle.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Mark Rutland <mark.rutland@....com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Chris Hyser <chris.hyser@...cle.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Gladkov <legion@...nel.org>,
        Ran Xiaokai <ran.xiaokai@....com.cn>,
        David Hildenbrand <david@...hat.com>,
        Xiaofeng Cao <caoxiaofeng@...ong.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Thomas Cedeno <thomascedeno@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Evgenii Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH v4 0/7] kernel: introduce uaccess logging

On Sat, Dec 11, 2021 at 9:23 AM David Laight <David.Laight@...lab.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