linux-kernel - Re: [PATCH] kernel: introduce prctl(PR_LOG

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Message-ID: <YUuJo7IfS4x0iLfX@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Sep 2021 21:53:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        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>,
        Colin Ian King <colin.king@...onical.com>,
        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>,
        Balbir Singh <sblbir@...zon.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>,
        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-arm-kernel@...ts.infradead.org,
        Evgenii Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH] kernel: introduce prctl(PR_LOG_UACCESS)

On Wed, Sep 22, 2021 at 03:22:50PM -0400, Steven Rostedt wrote:
> On Wed, 22 Sep 2021 19:46:47 +0200
> David Hildenbrand <david@...hat.com> wrote:
> 
> > > All signals except SIGKILL and SIGSTOP are masked for the interval
> > > between the prctl() and the next syscall in order to prevent handlers
> > > for intervening asynchronous signals from issuing syscalls that may
> > > cause uaccesses from the wrong syscall to be logged.  
> > 
> > Stupid question: can this be exploited from user space to effectively 
> > disable SIGKILL for a long time ... and do we care?
> 
> I first misread it too, but then caught my mistake reading it a second
> time. It says "except SIGKILL". So no, it does not disable SIGKILL.

Disabling SIGINT might already be a giant nuisance. Letting through
SIGSTOP but not SIGCONT seems awkward. Blocking SIGTRAP seems like a bad
idea too. Blocking SIGBUS as delivered by #MC will be hillarious.