From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Subject: Re: [PATCH v4 1/4] syscalls: Restore address limit after a syscall
Date: Wed, 22 Mar 2017 13:44:57 -0700
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To: Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Martin Schwidefsky <schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Dave Hansen <dave.hansen-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>, =?UTF-8?Q?Ren=C3=A9_Nyffenegger?= <mail-gLCNRsNSrVdVZEhyV+6z5nIPMjoJpjVV@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "Paul E . McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Pavel Tikhomirov <ptikhomirov-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>, Stephen Smalley <sds-+05T5uksL2qpZYMLLGbcSA@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "H . Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Kees
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On Wed, Mar 22, 2017 at 1:38 PM, Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
> This patch ensures a syscall does not return to user-mode with a kernel
> address limit. If that happened, a process can corrupt kernel-mode
> memory and elevate privileges.
>
> For example, it would mitigation this bug:
>
> - https://bugs.chromium.org/p/project-zero/issues/detail?id=990
>
> If the CONFIG_BUG_ON_DATA_CORRUPTION option is enabled, an incorrect
> state will result in a BUG_ON.

I'm a bit confused about this choice of configurability.  I can see
two sensible choices:

1. Enable this hardening feature: BUG if there's an exploitable bug.

2. Don't enable it at all.

While it's possible that silently papering over the bug is slightly
faster than BUGging, it will allow bugs to continue to exist
undetected.

--Andy