linux-kernel - Re: [PATCH v3 0/6] kernel: introduce uaccess logging

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Date:   Thu, 9 Dec 2021 14:12:03 -0800
From:   Peter Collingbourne <pcc@...gle.com>
To:     Marco Elver <elver@...gle.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>,
        Alexander Potapenko <glider@...gle.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Evgenii Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH v3 0/6] kernel: introduce uaccess logging

On Wed, Dec 8, 2021 at 7:33 AM Marco Elver <elver@...gle.com> wrote:
>
> On Wed, 8 Dec 2021 at 05:48, Peter Collingbourne <pcc@...gle.com> wrote:
> [...]
> > Peter Collingbourne (6):
> >   include: split out uaccess instrumentation into a separate header
> >   uaccess-buffer: add core code
> >   fs: use copy_from_user_nolog() to copy mount() data
> >   uaccess-buffer: add CONFIG_GENERIC_ENTRY support
> >   arm64: add support for uaccess logging
> >   Documentation: document uaccess logging
>
> I think it needs to be possible to disable the feature via a Kconfig
> option. Not all systems want or could even tolerate the additional
> overheads -- even though you say they are minimal elsewhere. For
> example, some embedded systems most likely have absolutely no use for
> this feature, and the increase in .text might be unacceptable. Certain
> features that we usually take for granted are no different (see
> init/Kconfig: FUTEX, EPOLL, .. etc). If you'd like it enabled by
> default, given the overheads are small enough, it can do "default y"
> and be configurable only "if EXPERT".

Okay, done.

> Is it possible to add a kselftest-style test to
> tools/testing/selftests? In addition to the basic tests, can certain
> non-trivial properties, like masking of signals, also be tested? I
> think that'd be extremely valuable, because I'm sure we'd have to
> backport this to several older kernels.

Yes, I've added a new patch with a kselftest. (Good thing I did,
because it (together with DEBUG_PREEMPT) uncovered a bug in the
pre/post-exit-loop code. Fixed in v4.)

Peter