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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] dma-buf: explicitely forbid exposing pages from get_user_pages() Content-Language: en-US To: =?UTF-8?Q?Christian_K=c3=b6nig?= , , , , , , , , CC: =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20260630080112.1117341-1-christian.koenig@amd.com> From: Lizhi Hou In-Reply-To: <20260630080112.1117341-1-christian.koenig@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF00012E82:EE_|BY5PR12MB4242:EE_ X-MS-Office365-Filtering-Correlation-Id: 01097a04-5a55-4109-943e-08dedc487ad1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|36860700016|1800799024|82310400026|376014|22082099003|18002099003|11063799006|56012099006|6133799003; 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)(23010399003)(36860700016)(1800799024)(82310400026)(376014)(22082099003)(18002099003)(11063799006)(56012099006)(6133799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: XbPmcbT1vnszd+2rjN76v2vylkgF8iMGX7pCbadarYU5dnHUQVRIXjHbYYZwwlDvwh/blXw6Z3tzaLD2RuA1WrAwtj9zVhl2sIEs9DZRxQ5NqoQT3RvnIRy+zLE+Zsa5eP5HrpHmNiIbohT8OAIz541VGsF2abjp8uR3dey+MwQlwDN1poWe6rbIqVYWELQpyWKmnaKV91pbbcaJ8Ge8D7B5alsuTRF4HDC4fo3EKxrs1H7KhEpoiD2FGT2f89nUCCPpQ7t31K1Tr+bQf7ekb16tPlOv0xwQygMK7ZVXFVfMfq2K29B2gZyv2+kOvVULJ7J9b7ELTN2i8XQ17Jemtl7EHOswgYGuyrxEFyV2YVpqeS7BVKGM/aiMtsl1yZRlz2Di2bWVKUgCKdxGxnCCwRJxx5mXBRvSkCUIbjvUPuwFjwyOWR49mYpGhO3/ktIo X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jul 2026 16:54:58.8676 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 01097a04-5a55-4109-943e-08dedc487ad1 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: CO1PEPF00012E82.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4242 On 6/30/26 01:01, Christian König wrote: > We recently had another incident where two drivers put pages they got from > get_user_pages() into a DMA-buf and cause quite a number of problems. > > Explicitely document that this is not something exporters can do. > > Signed-off-by: Christian König > --- > drivers/dma-buf/dma-buf.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 71f37544a5c6..aa5af4f439c2 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -685,6 +685,14 @@ static struct file *dma_buf_getfile(size_t size, int flags) > * > * For the detailed semantics exporters are expected to implement see > * &dma_buf_ops. > + * > + * It is explicitely forbidden for exporters to expose buffers they don't "own" > + * as DMA-buf. This includes pages acquired by get_user_pages() or other import > + * mechanism. Not following this rule can create numerous security problems. > + * > + * It is also strongly discouraged to expose the same backing store through > + * multiple DMA-bufs at the same time. This eventually creates aliasing and > + * cache coherency problems which are extremely hard to debug and fix. > */ Reviewed-by: Lizhi Hou > > /**