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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 21 Jun 2021 08:38:14 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michael Schmitz <schmitzmic@...il.com>,
        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: Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads

On Mon, Jun 21, 2021 at 6:55 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Tue, Jun 15, 2021 at 02:58:12PM -0700, Linus Torvalds wrote:
>
> > And I think our horrible "kernel threads return to user space when
> > done" is absolutely horrifically nasty. Maybe of the clever sort, but
> > mostly of the historical horror sort.
>
> How would you prefer to handle that, then?  Separate magical path from
> kernel_execve() to switch to userland?  We used to have something of
> that sort, and that had been a real horror...

Hmm. Maybe the alternatives would all be worse. The current thing is
clever, and shares the return path with the normal case. It's just
also a bit surprising, in that a kernel thread normally must not
return - with the magical exception of "if it had done a
kernel_execve() at some point, then returning is magically the way you
actually start user mode".

So it all feels very special, and there's not even a comment about it.

I think we only have two users of that thing (the very first 'init',
and user-mode-helpr), So I guess it doesn't really matter.

            Linus