linux-kernel - Re: Kernel stack read with PTRACE_EVENT_EXIT and io

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Message-ID: <87sg18abr6.fsf@disp2133>
Date:   Wed, 23 Jun 2021 09:36:45 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Michael Schmitz <schmitzmic@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...nel.org>, Tejun Heo <tj@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Subject: Re: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

Michael Schmitz <schmitzmic@...il.com> writes:

> Hi Eric,
>
> Am 23.06.2021 um 09:48 schrieb Michael Schmitz:
>>>
>>> The challenging ones are /proc/pid/syscall and seccomp which want to see
>>> all of the system call arguments.  I think every architecture always
>>> saves the system call arguments unconditionally, so those cases are
>>> probably not as interesting.  But they certain look like they could be
>>> trouble.
>>
>> Seccomp hasn't yet been implemented on m68k, though I'm working on that
>> with Adrian. The sole secure_computing() call will happen in
>> syscall_trace_enter(), so all system call arguments have been saved on
>> the stack.
>>
>> Haven't looked at /proc/pid/syscall yet ...
>
> Not supported at present (no HAVE_ARCH_TRACEHOOK for m68k). And the
> syscall_get_arguments I wrote for seccomp support only copies the first five
> data registers, which are always saved.

Yes.  It is looking like I can fix everything generically except for
faking user space registers for io_uring threads.

Eric