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x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfMbSJ12Oc/JXLmA8KZSa6YIglgc9QmYIWfg4sO2CMBoriHISSk9XjPgugfgDNieSU2UXL6Q+zJoyyZOVFEVTb6Pi+MAprl7EsirUFG6sq17FYm8mhoJc BvwjfyE/UhLXHg2xUOCtP+wV1cZ4T8BqjXlW5sa8ZSGktfGgLAHZZfqZGVDA9yJdbGl2tT/STjYwgBW4qeMaDu8viu4q+mWqkU4kMDtqPiXw/Bd6BuZUSL2m X-CM-Analysis: v=2.3 cv=NPP7BXyg c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=IkcTkHD0fZMA:10 a=VUJBJC2UJ8kA:10 a=yPCof4ZbAAAA:8 a=mVGBuK6AJzuDjYpWrm8A:9 a=eh7-vHDgZuLHz2N9:21 a=Pz2NRUZH-mo6gI-u:21 a=QEXdDO2ut3YA:10 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751854AbeEBO5u (ORCPT ); Wed, 2 May 2018 10:57:50 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:56720 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751853AbeEBO5t (ORCPT ); Wed, 2 May 2018 10:57:49 -0400 Subject: Re: [Xen-devel] [PATCH 3/4] xen/PVH: Set up GS segment for stack canary To: Jan Beulich Cc: xen-devel , Juergen Gross , linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20180430162339.17143-1-boris.ostrovsky@oracle.com> <20180430162339.17143-4-boris.ostrovsky@oracle.com> <5AE973CD02000078001C008E@prv1-mh.provo.novell.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <5AE973CD02000078001C008E@prv1-mh.provo.novell.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8880 signatures=668698 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=950 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1805020124 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 05/02/2018 04:16 AM, Jan Beulich wrote: >>>> On 30.04.18 at 18:23, wrote: >> --- a/arch/x86/xen/xen-pvh.S >> +++ b/arch/x86/xen/xen-pvh.S >> @@ -54,6 +54,9 @@ >> * charge of setting up it's own stack, GDT and IDT. >> */ >> >> +#define PVH_GDT_ENTRY_CANARY 4 >> +#define PVH_CANARY_SEL (PVH_GDT_ENTRY_CANARY * 8) > I can only advise against doing it this way: There's no safeguard against > someone changing asm/segment.h without changing this value (in fact > this applies to all of the GDT selectors populated in this file). At the very > least tie this to GDT_ENTRY_BOOT_TSS / __BOOT_TSS? > >> @@ -64,6 +67,9 @@ ENTRY(pvh_start_xen) >> mov %eax,%es >> mov %eax,%ss >> >> + mov $(PVH_CANARY_SEL),%eax >> + mov %eax,%gs >> + >> /* Stash hvm_start_info. */ >> mov $_pa(pvh_start_info), %edi >> mov %ebx, %esi >> @@ -150,6 +156,7 @@ gdt_start: >> .quad 0x00cf9a000000ffff /* __BOOT_CS */ >> #endif >> .quad 0x00cf92000000ffff /* __BOOT_DS */ >> + .quad 0x0040900000000018 /* PVH_CANARY_SEL */ > Without any further code before loading the selector, this points at > physical address 0. Don't you need to add in the base address of > the per-CPU stack_canary? This GDT is gone soon after we jump into generic x86 startup code.That code will load its own GDT (and then set up per-cpu segments and all that). -boris