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Tsirkin" , Stefan Hajnoczi Cc: israelr@nvidia.com, virtualization@lists.linux.dev, linux-block@vger.kernel.org, oren@nvidia.com, nitzanc@nvidia.com, dbenbasat@nvidia.com, smalin@nvidia.com, larora@nvidia.com, izach@nvidia.com, aaptel@nvidia.com, parav@nvidia.com, kvm@vger.kernel.org References: <20250224233106.8519-1-mgurtovoy@nvidia.com> <20250227081747.GE85709@fedora> <20250227034434-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Max Gurtovoy In-Reply-To: <20250227034434-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO4P265CA0099.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:2bc::20) To CY5PR12MB6369.namprd12.prod.outlook.com (2603:10b6:930:21::10) Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY5PR12MB6369:EE_|IA0PR12MB8206:EE_ X-MS-Office365-Filtering-Correlation-Id: e2d83a86-d5a8-41be-ea0a-08dd5736229c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; 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Tsirkin wrote: > On Thu, Feb 27, 2025 at 04:17:47PM +0800, Stefan Hajnoczi wrote: >> On Tue, Feb 25, 2025 at 01:31:04AM +0200, Max Gurtovoy wrote: >>> Hi, >>> >>> This patch series introduces safety checks in virtio-blk and virtio-fs >>> drivers to ensure proper handling of device-writable buffer lengths as >>> specified by the virtio specification. >>> >>> The virtio specification states: >>> "The driver MUST NOT make assumptions about data in device-writable >>> buffers beyond the first len bytes, and SHOULD ignore this data." >>> >>> To align with this requirement, we introduce checks in both drivers to >>> verify that the length of data written by the device is at least as >>> large as the expected/needed payload. >>> >>> If this condition is not met, we set an I/O error status to prevent >>> processing of potentially invalid or incomplete data. >>> >>> These changes improve the robustness of the drivers and ensure better >>> compliance with the virtio specification. >>> >>> Max Gurtovoy (2): >>> virtio_blk: add length check for device writable portion >>> virtio_fs: add length check for device writable portion >>> >>> drivers/block/virtio_blk.c | 20 ++++++++++++++++++++ >>> fs/fuse/virtio_fs.c | 9 +++++++++ >>> 2 files changed, 29 insertions(+) >>> >>> -- >>> 2.18.1 >>> >> There are 3 cases: >> 1. The device reports len correctly. >> 2. The device reports len incorrectly, but the in buffers contain valid >> data. >> 3. The device reports len incorrectly and the in buffers contain invalid >> data. >> >> Case 1 does not change behavior. >> >> Case 3 never worked in the first place. This patch might produce an >> error now where garbage was returned in the past. >> >> It's case 2 that I'm worried about: users won't be happy if the driver >> stops working with a device that previously worked. >> >> Should we really risk breakage for little benefit? >> >> I remember there were cases of invalid len values reported by devices in >> the past. Michael might have thoughts about this. >> >> Stefan > > Indeed, there were. This is where Jason's efforts to validate > length stalled. > > See message id 20230526063041.18359-1-jasowang@redhat.com > > I am not sure I get the motivation for this patch. And yes, seems to > risky especially for blk. If it's to help device validation, I suggest a > Kconfig option. The primary motivation for this patch is to improve spec compliance and enhance driver robustness. You're right that there are different cases to consider:     1. For correctly behaving devices (Case 1) and fully incorrectly behaving devices (Case 3), there's no change in behavior (Case 3 never worked anyway).     2. For devices reporting incorrect lengths but with valid data (Case 2), I understand the concern about breaking existing setups. To address the concerns about Case 2 while still moving towards better spec compliance,we can make them configurable, as Michael suggested. Some configuration options:     1. Via a Kconfig     2. Via module param     3. Via adding quirks for known non-compliant devices (identified by subsystem dev/vendor ids) that are otherwise functional.     4. Via virtio_has_feature(vdev, VIRTIO_F_VERSION_1) >