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Date: Wed, 28 Jun 2017 10:52:55 -0700
From: Kees Cook <keescook@...omium.org>
To: Thomas Garnier <thgarnie@...gle.com>, Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, 
	Paolo Bonzini <pbonzini@...hat.com>, Rik van Riel <riel@...hat.com>, Oleg Nesterov <oleg@...hat.com>, 
	Josh Poimboeuf <jpoimboe@...hat.com>, Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>, 
	Al Viro <viro@...iv.linux.org.uk>, Arnd Bergmann <arnd@...db.de>, 
	Dave Hansen <dave.hansen@...el.com>, David Howells <dhowells@...hat.com>, 
	Russell King <linux@...linux.org.uk>, Andy Lutomirski <luto@...capital.net>, 
	Will Drewry <wad@...omium.org>, Will Deacon <will.deacon@....com>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, 
	Pratyush Anand <panand@...hat.com>, Chris Metcalf <cmetcalf@...lanox.com>, 
	"x86@...nel.org" <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Linux API <linux-api@...r.kernel.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v10 1/3] x86/syscalls: Check address limit on user-mode return

On Tue, Jun 20, 2017 at 1:24 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Jun 14, 2017 at 6:12 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
>> Ensure the address limit is a user-mode segment before returning to
>> user-mode. Otherwise a process can corrupt kernel-mode memory and elevate
>> privileges [1].
>>
>> The set_fs function sets the TIF_SETFS flag to force a slow path on
>> return. In the slow path, the address limit is checked to be USER_DS if
>> needed.
>>
>> The addr_limit_user_check function is added as a cross-architecture
>> function to check the address limit.
>>
>> [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990
>>
>> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
>
> Thanks for reworking this series!
>
> The bad state correctly BUGs under the LKDTM test:
>
> [   21.171586] lkdtm: Performing direct entry CORRUPT_USER_DS
> [   21.172791] lkdtm: setting bad task size limit
> [   21.173742] ------------[ cut here ]------------
> [   21.174641] kernel BUG at ./include/linux/syscalls.h:220!
> ...
> [   21.193166] Call Trace:
> [   21.193617]  ? trace_hardirqs_on_thunk+0x1a/0x1c
> [   21.194443]  entry_SYSCALL64_slow_path+0x25/0x25
>
>
> Tested-by: Kees Cook <keescook@...omium.org>

Is everyone happy with this patch for x86? Does this need anything
more/different?

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

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