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Message-ID: <CAJcbSZGLAXmE_mFZMAZgioWExzm3A4vXBKLGJ7DZNAbJOcH8Zw@mail.gmail.com>
Date: Wed, 22 Mar 2017 13:49:51 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Andy Lutomirski <luto@...capital.net>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>,
Dave Hansen <dave.hansen@...el.com>, David Howells <dhowells@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>, Arnd Bergmann <arnd@...db.de>,
René Nyffenegger <mail@...enyffenegger.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Oleg Nesterov <oleg@...hat.com>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>, Stephen Smalley <sds@...ho.nsa.gov>,
Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>, Rik van Riel <riel@...hat.com>, Kees Cook <keescook@...omium.org>,
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"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Christian Borntraeger <borntraeger@...ibm.com>, Russell King <linux@...linux.org.uk>,
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X86 ML <x86@...nel.org>,
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"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v4 1/4] syscalls: Restore address limit after a syscall
On Wed, Mar 22, 2017 at 1:44 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Wed, Mar 22, 2017 at 1:38 PM, Thomas Garnier <thgarnie@...gle.com> 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.
We can default to BUGging. I think my approach was avoiding doing a
BUG_ON just to avoid breaking people.
>
> --Andy
--
Thomas
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