From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752230AbeERTES (ORCPT ); Fri, 18 May 2018 15:04:18 -0400 Received: from gateway23.websitewelcome.com ([192.185.49.124]:12058 "EHLO gateway23.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751049AbeERTEP (ORCPT ); Fri, 18 May 2018 15:04:15 -0400 X-Authority-Reason: nr=8 Subject: Re: [PATCH] kernel: sys: fix potential Spectre v1 To: Dan Williams , Thomas Gleixner Cc: Andrew Morton , Linux Kernel Mailing List , Alexei Starovoitov , Peter Zijlstra References: <20180515030038.GA11822@embeddedor.com> <20180515150859.1bccbd8d4543848b30fea859@linux-foundation.org> From: "Gustavo A. R. Silva" Message-ID: <50481b83-4c03-f354-bd11-cef7aecdd85f@embeddedor.com> Date: Fri, 18 May 2018 14:04:12 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 187.172.56.86 X-Source-L: No X-Exim-ID: 1fJkfl-000ArE-Qe X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: ([192.168.1.70]) [187.172.56.86]:52704 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 4 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/15/2018 05:57 PM, Dan Williams wrote: > On Tue, May 15, 2018 at 3:29 PM, Thomas Gleixner wrote: >> On Tue, 15 May 2018, Andrew Morton wrote: >>> On Mon, 14 May 2018 22:00:38 -0500 "Gustavo A. R. Silva" wrote: >>> >>>> resource can be controlled by user-space, hence leading to a >>>> potential exploitation of the Spectre variant 1 vulnerability. >>>> >>>> This issue was detected with the help of Smatch: >>>> >>>> kernel/sys.c:1474 __do_compat_sys_old_getrlimit() warn: potential >>>> spectre issue 'get_current()->signal->rlim' (local cap) >>>> kernel/sys.c:1455 __do_sys_old_getrlimit() warn: potential spectre issue >>>> 'get_current()->signal->rlim' (local cap) >>>> >>>> Fix this by sanitizing *resource* before using it to index >>>> current->signal->rlim >>>> >>>> Notice that given that speculation windows are large, the policy is >>>> to kill the speculation on the first load and not worry if it can be >>>> completed with a dependent load/store [1]. >>> >>> hm. Not my area, but I'm always willing to learn ;) >>> >>>> --- a/kernel/sys.c >>>> +++ b/kernel/sys.c >>>> @@ -69,6 +69,9 @@ >>>> #include >>>> #include >>>> >>>> +/* Hardening for Spectre-v1 */ >>>> +#include >>>> + >>>> #include "uid16.h" >>>> >>>> #ifndef SET_UNALIGN_CTL >>>> @@ -1451,6 +1454,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource, >>>> if (resource >= RLIM_NLIMITS) >>>> return -EINVAL; >>>> >>>> + resource = array_index_nospec(resource, RLIM_NLIMITS); >>>> task_lock(current->group_leader); >>>> x = current->signal->rlim[resource]; >>> >>> Can the speculation proceed past the task_lock()? Or is the policy to >>> ignore such happy happenstances even if they are available? >> >> Locks are not in the way of speculation. Speculation has almost no limits >> except serializing instructions. At least they respect the magic AND >> limitation in array_index_nospec(). > > I'd say it another way, because they don't respect the magic AND, we > just make the result in the speculation path safe. So, it's controlled > speculation. > Dan, What do you think about adding the following function to the nospec API: diff --git a/include/linux/nospec.h b/include/linux/nospec.h index e791ebc..81e9a77 100644 --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -55,4 +55,17 @@ static inline unsigned long array_index_mask_nospec(unsigned long index, \ (typeof(_i)) (_i & _mask); \ }) + + +#ifndef sanitize_index_nospec +inline bool sanitize_index_nospec(unsigned long index, + unsigned long size) +{ + if (index >= size) + return false; + index = array_index_nospec(index, size); + + return true; +} +#endif #endif /* _LINUX_NOSPEC_H */ And here is an example of its use: diff --git a/drivers/media/i2c/tvp7002.c b/drivers/media/i2c/tvp7002.c index 4599b7e..27b39c0 100644 --- a/drivers/media/i2c/tvp7002.c +++ b/drivers/media/i2c/tvp7002.c @@ -35,6 +35,8 @@ #include #include +#include + #include "tvp7002_reg.h" MODULE_DESCRIPTION("TI TVP7002 Video and Graphics Digitizer driver"); @@ -784,7 +786,7 @@ static int tvp7002_enum_dv_timings(struct v4l2_subdev *sd, return -EINVAL; /* Check requested format index is within range */ - if (timings->index >= NUM_TIMINGS) + if (!sanitize_index_nospec(timings->index, NUM_TIMINGS)) return -EINVAL; timings->timings = tvp7002_timings[timings->index].timings; This patter is very common. So, it may be a good idea to unify both bounds checking and the serialization of instructions into a single function. What do you think? Thanks -- Gustavo