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d="scan'208";a="16986654" Subject: Re: [PATCH 11/16] x86/spec-ctrl: Adjust DO_OVERWRITE_RSB to be shadow stack compatible To: Jan Beulich References: <20200501225838.9866-1-andrew.cooper3@citrix.com> <20200501225838.9866-12-andrew.cooper3@citrix.com> <3c01d6c3-5a61-018b-13df-6e75256f6d6c@suse.com> From: Andrew Cooper Message-ID: Date: Thu, 7 May 2020 14:25:31 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <3c01d6c3-5a61-018b-13df-6e75256f6d6c@suse.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Content-Language: en-GB X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL02.citrite.net (10.69.22.126) X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Xen-devel , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 07/05/2020 14:22, Jan Beulich wrote: > On 02.05.2020 00:58, Andrew Cooper wrote: >> @@ -114,6 +114,16 @@ >> sub $1, %ecx >> jnz .L\@_fill_rsb_loop >> mov %\tmp, %rsp /* Restore old %rsp */ >> + >> +#ifdef CONFIG_XEN_SHSTK >> + mov $1, %ecx >> + rdsspd %ecx >> + cmp $1, %ecx >> + je .L\@_shstk_done >> + mov $64, %ecx /* 64 * 4 bytes, given incsspd */ >> + incsspd %ecx /* Restore old SSP */ >> +.L\@_shstk_done: >> +#endif > The latest here I wonder why you don't use alternatives patching. > I thought that's what you've introduced the synthetic feature > flag for. We're already in the middle of an alternative and they don't nest.  More importantly, this path gets used on the BSP, after patching and before CET gets enabled. ~Andrew