From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753206AbeCaSQ6 (ORCPT <rfc822;w@1wt.eu>);
        Sat, 31 Mar 2018 14:16:58 -0400
Received: from userp2130.oracle.com ([156.151.31.86]:59970 "EHLO
        userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753045AbeCaSQ5 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 31 Mar 2018 14:16:57 -0400
Subject: Re: [PATCH] x86/xen: Delay get_cpu_cap until stack canary is
 established
To: Jason Andryuk <jandryuk@gmail.com>
Cc: Juergen Gross <jgross@suse.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20180319165804.10636-1-jandryuk@gmail.com>
 <c3075b0c-a60b-0809-e34b-223701a53b84@oracle.com>
 <CAKf6xps0HJecKM0gYSK+3BGhKknYp9Ydxr3S0oWBThtXeytegw@mail.gmail.com>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <ee25829c-e8de-1171-e54e-3b34206acc9e@oracle.com>
Date: Sat, 31 Mar 2018 14:10:49 -0400
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: <CAKf6xps0HJecKM0gYSK+3BGhKknYp9Ydxr3S0oWBThtXeytegw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8849 signatures=668697
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0
 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999
 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.0.1-1711220000 definitions=main-1803310188
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On 03/31/2018 01:38 PM, Jason Andryuk wrote:
> On Wed, Mar 21, 2018, 5:12 PM Boris Ostrovsky 
> <boris.ostrovsky@oracle.com <mailto:boris.ostrovsky@oracle.com>> wrote:
> 
>     On 03/19/2018 12:58 PM, Jason Andryuk wrote:
>      > Commit 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
>     introduced a
>      > call to get_cpu_cap, which is fstack-protected.  This is works on
>     x86-64
>      > as commit 4f277295e54c ("x86/xen: init %gs very early to avoid page
>      > faults with stack protector") ensures the stack protector is
>     configured,
>      > but it it did not cover x86-32.
>      >
>      > Delay calling get_cpu_cap until after xen_setup_gdt has
>     initialized the
>      > stack canary.  Without this, a 32bit PV machine crashes early
>      > in boot.
>      > (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
>      > (XEN) ----[ Xen-4.6.6-xc  x86_64  debug=n  Tainted:    C ]----
>      > (XEN) CPU:    0
>      > (XEN) RIP:    e019:[<00000000c10362f8>]
>      >
>      > And the PV kernel IP corresponds to init_scattered_cpuid_features
>      >    0xc10362f8 <+24>:    mov    %gs:0x14,%eax
>      >
>      > Fixes 2cc42bac1c79 ("x86-64/Xen: eliminate W+X mappings")
>      >
>      > Signed-off-by: Jason Andryuk <jandryuk@gmail.com
>     <mailto:jandryuk@gmail.com>>
>      >
> 
> 
>     Applied to for-linus-4.17
> 
> 
> Thanks. If it's not too late, can this be cc: stable? 


We can always try ;-)

This is 4.15 and 4.16 only, I believe.

-boris



> If not, I'll 
> submit the request after it is in Linus's tree.
> 
> -Jason
>