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Peter Anvin" , Ingo Molnar , Mario Limonciello , Thomas Gleixner , , Yazen Ghannam , , Penny Zheng , , "Mario Limonciello (AMD)" References: <20260825214805.39148-1-jason.andryuk@amd.com> <20260825214805.39148-3-jason.andryuk@amd.com> <20260831023016.GEapTnOHTbN8XZGe2j@fat_crate.local> <13e77e26-7b4e-452f-bc61-a84acadf37f0@amd.com> <20260901002705.GFapYb2c6fPJYqokRi@fat_crate.local> Content-Language: en-US From: Jason Andryuk In-Reply-To: <20260901002705.GFapYb2c6fPJYqokRi@fat_crate.local> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001D6:EE_|SJ1PR12MB6076:EE_ X-MS-Office365-Filtering-Correlation-Id: 2e9dd6b3-3509-42d3-efd3-08df082085c7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|23010399003|36860700016|1800799024|376014|13003099007|10067099003|6133799003|11063799006|4143699003|56012099006|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(82310400026)(23010399003)(36860700016)(1800799024)(376014)(13003099007)(10067099003)(6133799003)(11063799006)(4143699003)(56012099006)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 30gks7Ewlynm2LZUgg+50KhNi5QrHqoJS8UBocEs234TD62gpwevfG5TV+os07WCwSA3r9MJQoqieXdVpFqBiwxQOwcfytMvywLNEsgzxdeeNwW9jcII+WRawUzmqRrAeFGQHhiy5g99zSSh6/WBzucyv61o3bAerjAxiTb4HY3HpvvM4lMXCbTFfL5QEHNkIP4cBNBxTjOG2D/FsaVfIdNHGsZzTYoXdJIMKBS2d9pGmN32Tw9uYw8Dfi80VL55Vvk95FmqxjvH8wdWMxKbfjh7peHxlL6+QWcW0P5aDaOLEoyKAeF+wAPea9bmuJJgxJ2gPf3dwQz17DkYPtXFuSug5XiV7hs1z6K+wb0FjOrDKu0ymBLP28gWvbTkdxIU1urXeKygghCQm2q55YHPiHAaPIX35FP0m9BC/PszalyEpbsOhDv7CcdXniTwMxY8 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Sep 2026 11:59:48.5070 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2e9dd6b3-3509-42d3-efd3-08df082085c7 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ5PEPF000001D6.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ1PR12MB6076 On 2026-08-31 20:27, Borislav Petkov wrote: > On Mon, Aug 31, 2026 at 01:52:08PM -0400, Jason Andryuk wrote: >> No, the code and the comment are both correct as posted. It's just that I >> wrote the comment reversed from the code to state the positive property we >> want. > > So if amd_smn_init() succeeds, that means we have registered the PCI config > regions of the PCI roots, including the SMN ones, as IORESOURCE_EXCLUSIVE and > they won't be exported to userspace through /dev/mem and what not. > > So, any caller of __amd_smn_rw() should fail because it is coming from kernel > space and it can expect that userspace could interfere with the hw and thus > not a good idea. > > So yes, this is what got me confused and the (!amd_roots) check is correct. > >> I'll change this whichever way you want. It's not a big deal, which is why >> I added the comment like you requested originally. > > I think I already "intercepted" your suggestion, see here: > > From 1a1c4addc5a14e9ef2bb7d351a62ff4563d0f10a Mon Sep 17 00:00:00 2001 > From: Jason Andryuk > Date: Tue, 25 Aug 2026 17:48:03 -0400 > Subject: [PATCH] x86/amd_node: Prevent potential NULL pointer dereference > > amd_smn_read/write() are exported functions around __amd_smn_rw(), so > they are always available even if amd_smn_init() fails. In that case, > amd_roots is NULL and __amd_smn_rw() will access uninitialized memory. > > Then, commit > > 83518453074d ("x86/amd_node: Add SMN offsets to exclusive region access") > > added smn_exclusive which indicated the calls to > pci_request_config_region_exclusive() succeeded to prevent concurrent > userspace access. > > Commit > > 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") > > re-ordered initialization so pci_request_config_region_exclusive() is called > earlier and a failure exits amd_smn_init() before allocating amd_roots. > Setting smn_exclusive moved to the end of amd_smn_init(), after amd_roots is > allocated. It became redundant and can be removed. > > Replace smn_exclusive with directly checking amd_roots to avoid a potential > NULL pointer dereference. > > [ bp: Reorg commit message, touchup comment. ] > > Fixes: 77466b798d59 ("x86/amd_node: Remove dependency on AMD_NB") > Signed-off-by: Jason Andryuk > Signed-off-by: Borislav Petkov (AMD) > Reviewed-by: Yazen Ghannam > Reviewed-by: Mario Limonciello (AMD) > Cc: stable@vger.kernel.org > Link: https://patch.msgid.link/20260825214805.39148-3-jason.andryuk@amd.com Looks good to me. Thanks, Jason