From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=pass header.oldest-pass=0 smtp.remote-ip=52.101.201.3 ARC-Seal: i=2; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=pass; t=1794385132; b=NsSprfphVpuwF5yvvTzrc7ihtkfWM3opzRUEPslDRzkrKPFmSvHeul+vnWsAjDkG5fMa wh1fhHlnx70GIIdTLG/GJewaoITH3XLLSYmbHv8AZmumvId6rlwo/fVwoDLvHXc9hu30M RDQlHmBOIrVNBocgzAcXYG/RFvjgaaa7tb+n3qrRSgrDTSCFXvlpruU/+l2RYccugzMYC esncpAZye5ZI8viWaFjldKDa9oM7TsEKAZDlszWYPv4OAf0DPX6jFBa/o6dH+r1/nbRM/ NVLFWt2slXMc2JfAjQ0F2g1UNrGLU5S5ykTg70VY9NU4ocUeOs4GgZyTC9ASXLs5AAQ== ARC-Message-Signature: i=2; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794385132; h=DMARC-Filter:DKIM-Signature:Received:Received:Message-ID:Date: User-Agent:Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding:X-ClientProxiedBy:MIME-Version: X-MS-PublicTrafficType:X-MS-TrafficTypeDiagnostic: X-MS-Office365-Filtering-Correlation-Id:X-MS-Exchange-SenderADCheck: X-MS-Exchange-AntiSpam-Relay:X-Microsoft-Antispam: X-Microsoft-Antispam-Message-Info:X-Forefront-Antispam-Report: X-MS-Exchange-AntiSpam-MessageData-ChunkCount: X-MS-Exchange-AntiSpam-MessageData-0:X-OriginatorOrg: X-MS-Exchange-CrossTenant-Network-Message-Id: X-MS-Exchange-CrossTenant-AuthSource:X-MS-Exchange-CrossTenant-AuthAs: X-MS-Exchange-CrossTenant-OriginalArrivalTime: X-MS-Exchange-CrossTenant-FromEntityHeader: X-MS-Exchange-CrossTenant-Id:X-MS-Exchange-CrossTenant-MailboxType: X-MS-Exchange-CrossTenant-UserPrincipalName: X-MS-Exchange-Transport-CrossTenantHeadersStamped; bh=lrShLJ88cqiFfMjHf5yF10atqk/pMhGbbvLtXygq+N8=; b=Uco5/nP/RNAfB3JYRLlp1OD7hMUNqHeSJnDzbQYeyzL4Pp3H1DUz1j1MB7aMR3D8FzgV q2ia6F9/LfAAmvGlmG/JbkAYalTR9dGqwnEi9owSmXcoy4HL17pCbLIYxSf4Ua2k9iarJ DDeFrnmw6BCGHzNQFveWcU/XJLxfFcXBSh0N915/Hpr7HqeNUXzDyAe6lRvzPlLRvCSjk iXFHIbtHI0Zp7rXlLg5Wy3P+RG83CnRj9/FGnBmwleimaEnMu23MprqUTyF5o3hOdV0yA jJNs+GexmLwWqm0e8zm4ezDxREgXqOsA3Q5utpKPg+8X4tAm5hA5kLdpiVgxVaYDPGA== ARC-Authentication-Results: i=2; smtp.subspace.kernel.org; dmarc=pass header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass header.d=amd.com header.i=@amd.com header.a=rsa-sha256 header.s=selector1 header.b=irDrH+iL; arc=pass header.oldest-pass=0 smtp.remote-ip=52.101.201.3 Received: from PH7PR06CU001.outbound.protection.outlook.com (mail-westus3azon11010003.outbound.protection.outlook.com [52.101.201.3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (secp384r1) server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 83292606A31C; Wed, 11 Nov 2026 08:18:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 83292606A31C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=amd.com header.i=@amd.com header.a=rsa-sha256 header.s=selector1 header.b=irDrH+iL ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=ASufgGZPLl1g/rbE/CxqW7swUTep2raswLcEHX5xvq1JOKcNrvKLqfHpkxSbnE/ab9tm/KSo3XUZjj/KL1NYT2qajC07uVSNR/XmMlLITgj/xzlNz9XDuxYzhRVPlMvqMnevR1nAc8dHGae+gz+UcwVsFvLutXXWSyJihed59MeK2Wcak9gPXVZ48KFNtny+Xv3ToXI2nnfndiakx2knnmUGNVsSRGjf920sI0tjokBfveTp1QgU3fhyCman0SelXW0+iHjJ/N0316RXNO1ZO3+PTycD0g9kar74O16FuGkNv7QvWmyGM6BK3Tfm/xjezjvHYoVoJ3moBovfllHDFQ== 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=lrShLJ88cqiFfMjHf5yF10atqk/pMhGbbvLtXygq+N8=; b=tdFDJDZ5uXTcLu3q/JroZAhFCcX8fIBzVTRwRRbX6zUBqzw/vLoTjVgWqLaZq0CwYTzoDK3VpKla1lKP+Ha1hz83zb+lqSKlO9EB9u8aiCHnShBNKuoCEOHS1wnnILhpc+G+kj51t58/zQeIxQ1h9/wan5LCQ5a9z1NhIdu5oP105Vgalq7pBjjlMVwcQwYagawRUYVdw7LG1L6wYzluR1ooJW9lNDOkQavJd2+B8kP8F5p2qkTlANUMRD2S3I/HvLKsKpTuByndRAsxKHzwuKdx9va3M/P7e6ZotBcYeloIGlQrLwhnkZEiZCialL+RS8p0tCEnrk4ts661Chl90Q== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=amd.com; dmarc=pass action=none header.from=amd.com; dkim=pass header.d=amd.com; arc=none 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=lrShLJ88cqiFfMjHf5yF10atqk/pMhGbbvLtXygq+N8=; b=irDrH+iLGXG5RPPMz1yUavBV9mYuKbvIAhmWO2upuvHiKuEZv6wMTvtiX3ygQNRZgC2TbhDAL1d2iE8JoDZFlAw1Jwcwy/kp7Cup/X36xKGTA/cHNy90tC7IwLCc2TuoCHZF/ilcv1MM+4vHRVAo7kUFwK+cfTa/1YGcwuKyMgI= Authentication-Results: mx.microsoft.com 1; dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) by CH3PR12MB9217.namprd12.prod.outlook.com (2603:10b6:610:195::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.615.8; Wed, 11 Nov 2026 08:18:48 +0000 Received: from PH7PR12MB5685.namprd12.prod.outlook.com ([fe80::ce69:cfae:774d:a65c]) by PH7PR12MB5685.namprd12.prod.outlook.com ([fe80::ce69:cfae:774d:a65c%3]) with mapi id 15.21.0615.007; Wed, 11 Nov 2026 08:18:48 +0000 Message-ID: <1e7fe0eb-2b06-4db0-98b1-3535218847b3@amd.com> Date: Wed, 11 Nov 2026 09:18:43 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] bpf: make dmabuf iterator stay drained after NULL To: Kang Chen , Yonghong Song , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , "T.J. Mercier" Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Sumit Semwal , Philipp Stanner , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org References: <20261110125106.2935677-1-k.chen@smail.nju.edu.cn> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20261110125106.2935677-1-k.chen@smail.nju.edu.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR0P281CA0180.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:b4::10) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|CH3PR12MB9217:EE_ X-MS-Office365-Filtering-Correlation-Id: 2a99bd62-8c6c-44bb-8baf-08df3fcc6939 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014|23010399003|22082099003|18002099003|10067099003|11063799006|261028144727099003|261009223027099003|261026140227099003|261102123227099003|56012099006|261022105027099003|261021121427099003|261022075727099003|261021123027099003|261026121527099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:PH7PR12MB5685.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(7416014)(376014)(23010399003)(22082099003)(18002099003)(10067099003)(11063799006)(261028144727099003)(261009223027099003)(261026140227099003)(261102123227099003)(56012099006)(261022105027099003)(261021121427099003)(261022075727099003)(261021123027099003)(261026121527099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?ZlhtWXVtVWdCdk5CbUtmWDVydWl4NWorWmYwcmx6eUxHc01ERFVFYmZXWW81?= =?utf-8?B?Uzk0OUZNVUUzTWNkMHZQNk0rMEt4aENKdTU0R0c1UENnYVdrZ0hDVFZqMmlt?= =?utf-8?B?d1orb08xVG1PQklLL25zUU1PRTIxQ1Y3cGtPU1BteDJlVGlQdWs2WE1adk4r?= =?utf-8?B?N2NYNkFFY2R0Vk0xRVBKWkN3WGJFZFU1VDh3WldpZTFIdzRvM1FZYmRwVjI3?= =?utf-8?B?YTZIbENnQUhORGEra0tkQ2pVN2JIYlE1U0plWWZkdUdsbHZad3ZVRVFtOFMy?= =?utf-8?B?RFBiQXk3cVB5QW5lTXRyRzBNL3doQUEzMUxsS2ZhZWJYVHRqSWlUU3doblZJ?= =?utf-8?B?M2JubnIxWmsrZ1VqN1QzUmhvdlFtUCtWeXh3UnFoQ1Fta3ZxRGoxbEFqVHFl?= =?utf-8?B?T1B0ZDN6RndyRDRack54bkZsNUJodjcwY050RGxIUHBZQTdYM005RnphZERT?= =?utf-8?B?bVFqU1FHOEpZdnpwcTMzdG9mRU56MlMrcVFkMEJzV3JXbTBEaDNxVCtHWjdQ?= =?utf-8?B?dDRNZDZsMS9EMGFNa3dHNkdQaEZxM0JzNSt0UEVqUWlIRmJGdytFcWRISHd5?= =?utf-8?B?NWxaTnowOU9LOXVJUUE4RitwRFdOWTZNMG5LK1EycmEwdlJTeU5HM09GdTRV?= =?utf-8?B?b3ZGTnp3d1QwTWFHRkNac2IvOFhyVWh4bExFZEZXckNjOFdqVm9VakRRdjBz?= =?utf-8?B?SG5DRUVpaTRFeFFrY0dHaVpWREszWk9TWUN1TlhBRytFVDdRY2MvdUUrN2xx?= =?utf-8?B?MGZtaXNySXNpNzVvbytNdjRXYjRPOXpqK0ZwR0F4TXpMeXZMZ050bHBHUVM0?= =?utf-8?B?SFdaOFptWThDZHVET1ExYVliVDUxNzJCbENNcGlYcW13TGQ3T1d1Y05SeXB3?= =?utf-8?B?Q25LWDhKK2tEQ3NiU0R0Y2hKV29HZ2VDRmQzeDhNdFJSWGZhZlBVNTVWaHJ5?= =?utf-8?B?MDVMRXpReEMxM2FFVXlsWHZZcC9sNExDaEJad2dxMkhXYkxLeUE0TXdtN21T?= =?utf-8?B?bmNFeUtUOCtPYzhVbHArVi9OUDN5TmZ5SktHZDhyZWkybXVpSmNlMkZmcXRy?= =?utf-8?B?cmZSV1g5Y3F5MUpUVnFvRzZVSk5FZW1icHY1b2pYQmZaYjdXNHhNdnZSVmdx?= =?utf-8?B?QVNLNEtwVzU0YmZpUlhIZXBTZmxsUFp5VnJPM3V1S3BGbE9FZVEyb3NXWHBv?= =?utf-8?B?eFJBakFsK3ZaMk5Pa0phTUZlMExhU0R5UTJHVjIxQUx4TWpOY0JWcE5kUDBG?= =?utf-8?B?YUczRjlhTVBPM1dxUkpCRHFoY2MvWVUwTDhVR2ZlV0JjWHRLNzM5M3pVUlhu?= =?utf-8?B?cHlsSjJST2lKZFVqTkVzdHdBV2MwcUhySHE2SElVQzlMTG4yL3A0L0tRM1dE?= =?utf-8?B?SzRKL1Q5akRMbGlBOEpEN1UzN2tTczgzeVlyZkpVUEt5cnFrQzIyK0l2a3BF?= =?utf-8?B?MWRDa3dSN1VUNmZFRlg3MzB4QTU0TDljTm5aUkU5eVBQWkh5TlhLeGhDYzBM?= =?utf-8?B?QU9DVmc1dWpLSkhPNTRKNzQyZ05Jd1J2emxIdms4UUpyUmUzNnJKcWtjY2Fy?= =?utf-8?B?ZHY0ZWtjWTRleXZKN3JVVWhob2RRaUFkTEE3QWZFY0ltbTdQbkVqK0RIUUdG?= =?utf-8?B?NGVvenQ5VXFhM09yYUwvZjAwcDFuY25UZWRaeWo3TXc0dDNhYjU1OGViZGk5?= =?utf-8?B?RFN6eWVYN3h3bkRITGxKOXFVdnJwa3lZdlVSVXBSdUdCL0lwSzdBL2xvWTJu?= =?utf-8?B?WFN2QlJPeWkxdFVNVzZ2dk9JOGp0M2VpeHgrSEVyMGY3aWpqWWdhYXZscFVF?= =?utf-8?B?bDVsK0t3SElvcHQ5QUovNTB4VVBKUW01eUMzRkVNZTZWRGtobSswTWxiOUhZ?= =?utf-8?B?WklITi9nRlNxbHhkR3ZGbEJKMUZ0OXhmTGdENzA0SDdaNjZwczdCS0gyVmxL?= =?utf-8?B?dlE0bzZ0UTN6TDZCTU9pYmFvMHkxdVRqTVZMNjVvSTZWSGU5eFFNS2M2MVow?= =?utf-8?B?RWxGT04vd3pFd1pSSzRuVnZ0VGVOUXN4aUwxQTNpL29RTHozK3dwUnBEdndJ?= =?utf-8?B?Znd4WDAyVXhOc1BXSjBDanFVaENlSEE4ZFdUOWNwT1JTZjQ0UGt0bVI0a2kv?= =?utf-8?B?ZVJsTitsVjB5TlJmbnppRmVYaUxySmQ1RUkreGVucmc2VWlWOVRkSGppUEdm?= =?utf-8?B?NUdKSkpoZFdlUWdkc3prcGRDekFmR05Ua2FPaXd4WVM2cFRNM3A3cXMwSlBT?= =?utf-8?B?bE5reUtoL25weGRQYmJwMDF4dU5ZMHNRR3ZWYXFNbEI2NENsR2xuWHkyZFIr?= =?utf-8?Q?ytsMznO05HjUMteTtD?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2a99bd62-8c6c-44bb-8baf-08df3fcc6939 X-MS-Exchange-CrossTenant-AuthSource: PH7PR12MB5685.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Nov 2026 08:18:48.2942 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: xFqbuovGKa1j/mxgfeQJf4x047zHndh2Sihxhj+KTIWmRip5/c9LzhrFwqjDwyuW X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB9217 Adding T.J. to comment. Regards, Christian. On 11/10/26 13:51, Kang Chen wrote: > bpf_iter_dmabuf_next() uses kit->dmabuf == NULL to mean "iteration has > not started". dma_buf_iter_next() also returns NULL at the end of the > list, so a next() call after exhaustion restarts from the list head. > > The verifier relies on the iterator contract that once next() returns > NULL it keeps returning NULL: process_iter_next_call() marks the > iterator DRAINED and treats the result of later next() calls as the > constant zero. A restarted dmabuf iteration therefore hands the BPF > program a kernel pointer while the verifier believes R0 == 0. > > Use an invalid pointer value as the drained sentinel so the iterator > state keeps its one-pointer ABI, and skip dma_buf_put() for it. > > Fixes: 6eab7ac7c5ee ("bpf: Add open coded dmabuf iterator") > Signed-off-by: Kang Chen > --- > kernel/bpf/dmabuf_iter.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/kernel/bpf/dmabuf_iter.c b/kernel/bpf/dmabuf_iter.c > index cd500248abd9..a2b7c38f9ae6 100644 > --- a/kernel/bpf/dmabuf_iter.c > +++ b/kernel/bpf/dmabuf_iter.c > @@ -156,6 +156,13 @@ struct bpf_iter_dmabuf_kern { > struct dma_buf *dmabuf; > } __aligned(8); > > +/* > + * The iterator state is one pointer wide because struct bpf_iter_dmabuf is > + * part of the generated vmlinux.h ABI. Use an invalid pointer value as the > + * "drained" sentinel instead of growing the state. > + */ > +#define DMABUF_ITER_DONE ((struct dma_buf *)1L) > + > __bpf_kfunc_start_defs(); > > __bpf_kfunc int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) > @@ -173,11 +180,25 @@ __bpf_kfunc struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it) > { > struct bpf_iter_dmabuf_kern *kit = (void *)it; > > + /* > + * The verifier assumes that an iterator which returned NULL keeps > + * returning NULL (see process_iter_next_call()). Without this check > + * the NULL left by the last dma_buf_iter_next() would be interpreted > + * as "not started" and the iteration would restart from the list head. > + */ > + if (kit->dmabuf == DMABUF_ITER_DONE) > + return NULL; > + > if (kit->dmabuf) > kit->dmabuf = dma_buf_iter_next(kit->dmabuf); > else > kit->dmabuf = dma_buf_iter_begin(); > > + if (!kit->dmabuf) { > + kit->dmabuf = DMABUF_ITER_DONE; > + return NULL; > + } > + > return kit->dmabuf; > } > > @@ -185,7 +206,7 @@ __bpf_kfunc void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) > { > struct bpf_iter_dmabuf_kern *kit = (void *)it; > > - if (kit->dmabuf) > + if (kit->dmabuf && kit->dmabuf != DMABUF_ITER_DONE) > dma_buf_put(kit->dmabuf); > } > > -- > 2.34.1 >