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 72EFCC369C2 for ; Fri, 25 Apr 2025 12:54:31 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.968020.1357723 (Exim 4.92) (envelope-from ) id 1u8IZQ-0005Mm-5U; Fri, 25 Apr 2025 12:54:20 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 968020.1357723; Fri, 25 Apr 2025 12:54:20 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1u8IZQ-0005Mf-1X; Fri, 25 Apr 2025 12:54:20 +0000 Received: by outflank-mailman (input) for mailman id 968020; Fri, 25 Apr 2025 12:54:18 +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 1u8IZO-0005MU-Ps for xen-devel@lists.xenproject.org; Fri, 25 Apr 2025 12:54:18 +0000 Received: from NAM11-DM6-obe.outbound.protection.outlook.com (mail-dm6nam11on20615.outbound.protection.outlook.com [2a01:111:f403:2415::615]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 63a82c91-21d4-11f0-9ffb-bf95429c2676; Fri, 25 Apr 2025 14:54:15 +0200 (CEST) Received: from MW4PR04CA0228.namprd04.prod.outlook.com (2603:10b6:303:87::23) by CH3PR12MB8659.namprd12.prod.outlook.com (2603:10b6:610:17c::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8678.27; Fri, 25 Apr 2025 12:54:10 +0000 Received: from SJ5PEPF000001F1.namprd05.prod.outlook.com (2603:10b6:303:87:cafe::91) by MW4PR04CA0228.outlook.office365.com (2603:10b6:303:87::23) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.20.8655.35 via Frontend Transport; Fri, 25 Apr 2025 12:54:09 +0000 Received: from SATLEXMB04.amd.com (165.204.84.17) by SJ5PEPF000001F1.mail.protection.outlook.com (10.167.242.69) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8655.12 via Frontend Transport; Fri, 25 Apr 2025 12:54:09 +0000 Received: from localhost (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Fri, 25 Apr 2025 07:54:07 -0500 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: 63a82c91-21d4-11f0-9ffb-bf95429c2676 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=OPgPAoxhY6BD/oqQ0O3/m0Dia8mgL+WWu/tLvNtwNsR2yU+etoUyuyr3HyoGHAAIii9Tn576pQXzKX3H3HxDoOfB0dxX5RFQv04sFC9ZN7XxMs66YMaymz72MGYU5I2GwD+3p72t46TszCNxR6+iBVE2SDSS9idDr7AcQIgtQzt0bPADNNfZ9B+CwmLk0tmIUx4zF7m/9Gbop4oHxtZZtvF7HiA08DanPBf5MM5D2FVW+UF9icSRBBXY/dSKe5kuAN/YEDL1Ic8toT+uL3lbzSYZwvgo3e680ndym1OSxCGU9IcxnEwsjnWetVtJLGEPnEmHvuoNpyfgLvmnyurvdw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=DpA0IsOcL84k4K+IiDU2FFoW7pmc4NixteRXMA26fP4=; b=RvegQIwJysy+e86tYHFbYQ3LWiHR82Hv2QVPO7VaRy41YZmZZlv8B+OLHw0hgLR6zFf85bKR2SuyN7pqlF2TuG7+pMMyvBGSOtw1MPQswsqC8IJg5SYphXqfEzNd7L2Y38MneAARWAipbxP7N6wfd495b6M5YJYnyf+qC7lidCpfjCuttis3KZCKiwuj+DO21cRSC/NgnPATZrIs6UVjQPpKefUEFR4FS9dwfU0JxN7WksWgC/Mzf5uXiiCa0T19tFqsRRqH7o99caE+6i6aMvTNvX3zFEm+sVzNgTqG7O77VEsjYXDPl0xL3ZT7Q8wS4D7NFWb6dIwlCov0S/6fwg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 165.204.84.17) smtp.rcpttodomain=citrix.com smtp.mailfrom=amd.com; dmarc=pass (p=quarantine sp=quarantine pct=100) action=none header.from=amd.com; dkim=none (message not signed); arc=none (0) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=DpA0IsOcL84k4K+IiDU2FFoW7pmc4NixteRXMA26fP4=; b=PmB7tg6dd8jhOgS3uC4oAUebnY6XvqXO8s+pr1gdb2j+ZNlUNymxE4DRr59bI+Xbf+lbT4w9HyFJsZBpQaYersMVk1oFLI4guSIGeSOYEPinoynoD6DLEOFXsKP8Kf/r1W1/izU5d3webaZc7NkIenot6RpnNmTogT3BBBTPa1Y= X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 165.204.84.17) smtp.mailfrom=amd.com; dkim=none (message not signed) header.d=none;dmarc=pass action=none header.from=amd.com; Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="UTF-8" Date: Fri, 25 Apr 2025 13:54:06 +0100 Message-ID: CC: , Jan Beulich , Andrew Cooper , Anthony PERARD , Xen-devel Subject: Re: [PATCH] x86/hvmloader: fix usage of NULL with cpuid_count() From: Alejandro Vallejo To: =?utf-8?q?Roger_Pau_Monn=C3=A9?= X-Mailer: aerc 0.20.1 References: <20250424125813.96449-1-roger.pau@citrix.com> In-Reply-To: X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001F1:EE_|CH3PR12MB8659:EE_ X-MS-Office365-Filtering-Correlation-Id: 4c17ae63-5183-4ab8-96e7-08dd83f8453c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|82310400026|1800799024|36860700013|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?OWhaMlIvN2pvbFJKcmdjVGNkak1rQVhFc3RrOHhvT0k3S3F2cmY4b3lCK1Nt?= =?utf-8?B?aDFoTkY3cHdaekVhdkZVc0xPQmdSODIxd1RTUVZETVArOUxGdXlSTGVUL1pD?= =?utf-8?B?RFJpM29YVGZrUUtrQ0s1TXdGdkE0WGJmay94cHk1SnkvcnhFbnozazRCdkxT?= =?utf-8?B?b0N3dkcvOERDTjJZT2R2azZDWFNWNDlyZ253bXd6TEJBeFlGTlMxYzQ1Nk4x?= =?utf-8?B?b1V6ZmhxQ0VJZGtwSFNxWmhWR2RieWk5Y09ZeWl1RDhMQk96a2doWmN4dlRR?= =?utf-8?B?bW9leUxqbE1lY2dRRUNVdEx5bzZBelhWTHhzL21kSFJlMWt6Sno1Nmh3aGpn?= =?utf-8?B?N0hudkJLVnBnNFY1a1V2VUI1VGJXdFRQTzNEU3hZVGhIRXhwZVRNSXBhQ1JT?= =?utf-8?B?TjQ4a2hKcUlrVEcwSUNzZ09VVVFOcUJyOEc0aHFWck9XcjMrVHhhR0Z5ajFn?= =?utf-8?B?amtZRjJwZFRFbXBWcnJOOUtHQ0tEeUlPVmNrcW9tdnhROHArOXoxMEN1TVlV?= =?utf-8?B?TkpnZ0c5aGJxL3o1QU1NWXYybEpzZWkzOXBXNWFzRDdqeE9pay9OVDJtejc5?= =?utf-8?B?VDIzZy9tMmJXMStwNDNXN0d0QTk5NzR3WjFobW91RHR6ZGlxbWp1SmRCTVV6?= =?utf-8?B?czhXS1hoMnVRdHBRTnNFNGxScE9SaXlpSmh1c3ZtQ1NXRTNvSHo4YXM0V2Nt?= =?utf-8?B?OXUwVTA2NENKRERNUW84OExtMENaNXMwMWU5QktZcSttL0FZYi9RRlNYNTlO?= =?utf-8?B?WWlVb1lEZEYyT2ZsSlYwdEJRWDVGWmJaZHRtQ3Rua2NIUmlFTzEyTHFUVFJx?= =?utf-8?B?VGI2WFF4RFlUTkpVdzI4Y2d0RGtmcWIxd3FFbmdteEs2UVlCN2V3M0ZqWFZj?= =?utf-8?B?OW1kZC80blNuL2NTVzZaM3dnZktqU3hiTnhoMHA2dERPTXdMamhBNS84UTNa?= =?utf-8?B?RWdtSWhyNHg2d205NDFFMEhWR0RqMTdPS0xlbUgzZk5TcFpnSWJVM2xqbkhF?= =?utf-8?B?bi9LYUVLWVZsajVXckZBTU1oVTFKYlF0WnRmdXpaUFpycUNLVlU4cGR2WnV1?= =?utf-8?B?SElsd3ZXclhwTkJVVXovT2t4b2I3NUdFb0dwQjdLbW1LdFJkTHZzNTdjYkJz?= =?utf-8?B?N0F1aGZEcHRvUEl2d0NrRzJqMFcxL1RxU3lSUkVRbG96WDBnQ1FIYXZFSzds?= =?utf-8?B?aFpWU2tSeDNwekVBL1JlQWVEVFluMWdRbm1BL2s4N3NXSHR5WW5XeW9nRFcw?= =?utf-8?B?NVpSNFZQL0xZWXpIZGxHUE93OGJvU2pUWVZtaGlmRkZVWm5MbGVQMXl2ZUdP?= =?utf-8?B?cjZCSndrdVdKY3RNeEFEemRQaDB6a3hYS0MyaWdQYW50czdRYzIvSUs5blE5?= =?utf-8?B?SVFBWnJ5eENmMFRRTlJEajE0TVQwVXJsMnpDUWVEZHp1NUsxbENhOXdIc2Qy?= =?utf-8?B?b0R4VjBOazJubXJXWWhOdlJrbDhMZnd6MkFWQWZSMnFBQTF4R1RiMDRDaDlh?= =?utf-8?B?QmJWQkhGQ3JDeTZVQUZXM0JxVUVBN3R6OEFxMmRmY3JPb1I1SHJqbzc2TXZQ?= =?utf-8?B?R1FHaGJ1M2RIUDdwWXBlMk9WNG5nWk1ac0VaaURCclRuZFJIMzlKd3NhU2s2?= =?utf-8?B?MGYrU2VaWWpQaUZLWEwwbitwSTZXK1BZMUN5Uzlobm5JVWFlYVROVkNUOEUx?= =?utf-8?B?T3BqMXR0cUpRVEhqZHViSDZpdWlDTHNXMURIeWV0dTc2bUJNeXlycjdqT0wx?= =?utf-8?B?R3FiNlFMa2V0cWJXeUFVeUpWOVdQMU4valhoVXMvbGV5M1dOMWhzL0JJamNw?= =?utf-8?B?bk12S08wZHpFaXFaWmJHZGVROFpXVzF6WnlFci95VnlVUWlKU1lmR21kWFBW?= =?utf-8?B?cGtJcGZRME4xdFl1UTZwMmNhMnhaVmdQRVdQR2RYc05IZGg2WG9LSjN1K1Z5?= =?utf-8?B?ZlJkc1dRbDdQN2FiWnJ4VDhXRFJmdWV4VnZCdUVPS2dXQXhTakRKbXJybVJy?= =?utf-8?B?eWUzdnA1Q25RRE80b0xHcjdqeWlicElnVFRVWVU3Unh5NzhXa2pwVHFtNWFk?= =?utf-8?Q?0MDB9+?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(376014)(82310400026)(1800799024)(36860700013)(7053199007);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Apr 2025 12:54:09.1799 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4c17ae63-5183-4ab8-96e7-08dd83f8453c X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001F1.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8659 On Fri Apr 25, 2025 at 1:44 PM BST, Roger Pau Monn=C3=A9 wrote: > On Fri, Apr 25, 2025 at 01:23:30PM +0100, Alejandro Vallejo wrote: >> On Thu Apr 24, 2025 at 1:58 PM BST, Roger Pau Monne wrote: >> > The commit that added support for retrieving the APIC IDs from the APs >> > introduced several usages of cpuid() with NULL parameters, which is no= t >> > handled by the underlying implementation. For GCC I expect this resul= ts in >> > writes to the physical address at 0, however for Clang the generated c= ode >> > in smp.o is: >> > >> > tools/firmware/hvmloader/smp.o: file format elf32-i386 >> > >> > Disassembly of section .text: >> > >> > 00000000 : >> > 0: 55 pushl %ebp >> > 1: 89 e5 movl %esp, %ebp >> > 3: 53 pushl %ebx >> > 4: 31 c0 xorl %eax, %eax >> > 6: 31 c9 xorl %ecx, %ecx >> > 8: 0f a2 cpuid >> > >> > Showing the usage of a NULL pointer results in undefined behavior, and >> > clang refusing to generate further code after it. >> > >> > Fix by using a temporary variable in cpuid_count() in place for any NU= LL >> > parameter. >> > >> > Fixes: 9ad0db58c7e2 ('tools/hvmloader: Retrieve APIC IDs from the APs = themselves') >> > Signed-off-by: Roger Pau Monn=C3=A9 >>=20 >> Ugh, that's on me. I was sure I saw the pattern in Xen (from where the >> code came from), but clearly I hallucinated. >>=20 >> > --- >> > Could also be fixed by using the temporary variable in the call sites, >> > however that's more code in the call sites at the expense of less chec= king. >> > I don't think the extra NULL check logic in cpuid_count() is that bad. >> > >> > Overall the solution proposed in this patch is safer going forward, as= it >> > prevent issues like this from being introduced in the first place. >>=20 >> Might be worth moving this same extra checks onto Xen's cpuid. There's >> no shortage of `junk` variables at the callsites. >>=20 >> > --- >> > tools/firmware/hvmloader/util.h | 11 +++++++++++ >> > 1 file changed, 11 insertions(+) >> > >> > diff --git a/tools/firmware/hvmloader/util.h b/tools/firmware/hvmloade= r/util.h >> > index 644450c51ceb..765a013ddd9e 100644 >> > --- a/tools/firmware/hvmloader/util.h >> > +++ b/tools/firmware/hvmloader/util.h >> > @@ -190,6 +190,17 @@ static inline void cpuid_count( >> > uint32_t *ecx, >> > uint32_t *edx) >> > { >> > + uint32_t tmp; >> > + >> > + if ( !eax ) >> > + eax =3D &tmp; >> > + if ( !ebx ) >> > + ebx =3D &tmp; >> > + if ( !ecx ) >> > + ecx =3D &tmp; >> > + if ( !edx ) >> > + edx =3D &tmp; >> > + >>=20 >> A somewhat more compact alternative that doesn't require tmp would be: >>=20 >> eax =3D eax ?: &leaf; >> ebx =3D ebx ?: &leaf; >> ecx =3D ecx ?: &leaf; >> edx =3D edx ?: &leaf; > > But that performs the write unconditionally? It might be more compact > code-wise, but might incur in an unneeded store? Pretty sure it would all optimise to very similar, if not identical code. > >> It clobbers `leaf`, but only after it's no longer relevant. > > My preference was to use a explicitly tmp variable, but I could switch > to using leaf if that's the preference. Given that Andrew has already > Acked the current version I'm tempted to just go with what has already > been Acked. That's perfectly fine. It was merely a cosmetic nit. LGTM as it is too. > > Thanks, Roger. Cheers, Alejandro