linux-kernel - Re: [PATCH] alpha: Add extra switch_stack frames in exit, exec, and kernel threads

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Message-ID: <YMpkHpZo4zx01Hw4@zeniv-ca.linux.org.uk>
Date:   Wed, 16 Jun 2021 20:50:38 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Michael Schmitz <schmitzmic@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Tejun Heo <tj@...nel.org>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] alpha: Add extra switch_stack frames in exit, exec, and
 kernel threads

On Tue, Jun 15, 2021 at 02:36:38PM -0500, Eric W. Biederman wrote:
> 
> While thinking about the information leaks fixed in 77f6ab8b7768
> ("don't dump the threads that had been already exiting when zapped.")
> I realized the problem is much more general than just coredumps and
> exit_mm.  We have io_uring threads, PTRACE_EVENT_EXEC and
> PTRACE_EVENT_EXIT where ptrace is allowed to access userspace
> registers, but on some architectures has not saved them.

Wait a sec.  To have anything happen on PTRACE_EVENT_EXEC, you need the
fucker traced.  *IF* you want to go that way, at least make it conditional
upon the same thing.