From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D2F01C433EF for ; Fri, 10 Dec 2021 17:16:44 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.244109.422236 (Exim 4.92) (envelope-from ) id 1mvjVG-0006tE-Qe; Fri, 10 Dec 2021 17:16:14 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 244109.422236; Fri, 10 Dec 2021 17:16:14 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mvjVG-0006t7-NQ; Fri, 10 Dec 2021 17:16:14 +0000 Received: by outflank-mailman (input) for mailman id 244109; Fri, 10 Dec 2021 17:16:13 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mvjVF-0006t1-PG for xen-devel@lists.xenproject.org; Fri, 10 Dec 2021 17:16:13 +0000 Received: from ppsw-42.csi.cam.ac.uk (ppsw-42.csi.cam.ac.uk [131.111.8.142]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id ded68ef4-59dc-11ec-ad7a-b7ef48004f0a; Fri, 10 Dec 2021 18:16:12 +0100 (CET) Received: from hades.srcf.societies.cam.ac.uk ([131.111.179.67]:36146) by ppsw-42.csi.cam.ac.uk (ppsw.cam.ac.uk [131.111.8.138]:25) with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) id 1mvjVC-00059H-87 (Exim 4.95) (return-path ); Fri, 10 Dec 2021 17:16:10 +0000 Received: from [192.168.1.10] (host-92-12-61-86.as13285.net [92.12.61.86]) (Authenticated sender: amc96) by hades.srcf.societies.cam.ac.uk (Postfix) with ESMTPSA id 54EC1200D8; Fri, 10 Dec 2021 17:16:10 +0000 (GMT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: ded68ef4-59dc-11ec-ad7a-b7ef48004f0a X-Cam-AntiVirus: no malware found X-Cam-ScannerInfo: https://help.uis.cam.ac.uk/email-scanner-virus Message-ID: <23feef0d-2913-69cf-1a1f-59b1e933ad37@srcf.net> Date: Fri, 10 Dec 2021 17:16:10 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.2 Content-Language: en-GB To: Jan Beulich , Andrew Cooper Cc: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , Xen-devel References: <20211126123446.32324-1-andrew.cooper3@citrix.com> <20211126163830.30151-1-andrew.cooper3@citrix.com> From: Andrew Cooper Subject: Re: [PATCH v1.1 64/65] x86/efi: Disable CET-IBT around Runtime Services calls In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 06/12/2021 11:06, Jan Beulich wrote: > On 26.11.2021 17:38, Andrew Cooper wrote: >> --- a/xen/arch/x86/efi/stub.c >> +++ b/xen/arch/x86/efi/stub.c >> @@ -11,6 +11,8 @@ >> #include >> #include >> >> +bool __initdata efi_no_cet_ibt; > I'm having trouble seeing what this is needed for - when this file gets > built, neither boot.c nor runtime.c will get compiled, and hence there > should not be any reference to the symbol that needs satisfying. > >> @@ -735,6 +736,14 @@ static void __init efi_init(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTabl >> >> StdOut = SystemTable->ConOut; >> StdErr = SystemTable->StdErr ?: StdOut; >> + >> +#ifdef CONFIG_X86 > CONFIG_XEN_IBT? > >> + /* >> + * Heuristic. Look under an arbitrary function pointer to see if UEFI was >> + * compiled with CET-IBT support. Experimentally some are not. >> + */ >> + efi_no_cet_ibt = !is_endbr64(efi_rs->GetTime); > I'm afraid I consider this insufficient. Even if the core EFI was built > with IBT support, some driver may not have been. That's not an issue.  Everything is built together in practice. > Hence I think there > needs to be a command line control to force turning off IBT. The only > question is whether we want to also honor its positive form - that > would, afaict, be a recipe for a guaranteed crash if used wrongly (and > it would be meaningless when used on IBT-aware firmware). It turns out that IBT support is lacking from tianocore, so nothing is going to support IBT for a good while yet. https://bugzilla.tianocore.org/show_bug.cgi?id=3726 is the proposed change to the spec to support this. In the meantime, I'm just going to blanket disable IBT for RS calls. ~Andrew