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Tue, 10 Mar 2020 14:37:25 +0000 Cc: brijesh.singh@amd.com, gary.hook@amd.com, erdemaktas@google.com, rientjes@google.com, npmccallum@redhat.com, bsd@redhat.com, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions To: Connor Kuehl , thomas.lendacky@amd.com, herbert@gondor.apana.org.au, davem@davemloft.net References: <20200306172010.1213899-1-ckuehl@redhat.com> <20200306172010.1213899-2-ckuehl@redhat.com> From: Brijesh Singh Message-ID: Date: Tue, 10 Mar 2020 09:37:21 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 In-Reply-To: <20200306172010.1213899-2-ckuehl@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SN4PR0201CA0057.namprd02.prod.outlook.com (2603:10b6:803:20::19) To CY4PR12MB1926.namprd12.prod.outlook.com (2603:10b6:903:11b::11) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.236.31.95] (165.204.77.1) by SN4PR0201CA0057.namprd02.prod.outlook.com (2603:10b6:803:20::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2793.16 via Frontend Transport; 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X-Microsoft-Antispam-Message-Info: w+PvEbvF8B5KfMMuXq+XVBZfgYKc1PZgX4WuOnIARzQcBeHTeD7ZjTBpsIs3lJ9bzMgLFH8yDpwReA00hcIwfU8ylFPnnW6PjY5AoQagjCXyb69mtnueTvFnOOM5VGy/x3rQjQrIUaq9pdJx0bsAxTYapdJQdDOkrJ4sDN26Q7BY6VF3BvyY0MHXCL2WFwFEBPchLnlqzRISwWUkQmyfR9OG0hw96nKQtU02Eiau+YLre/Cf28SOY3hYB33W3/mfHGETP6DGCAWjN6m0gU5C66trZ37yAnzDkmQ4yRfD9D0/ud40FdxnkPVwLnd9dzdldnGHOphQBGLt/v7F/FhBpbFU5PIGLDIG8VfHbUgOb51oIBi2wfcJ6PD6YOFRNm3Ez56lFwH/+ZIF1GY5aDdk2A59tgengmLjjoTy5dCfk7Hg9mGXzZoILUnpmPw+lfKD X-MS-Exchange-AntiSpam-MessageData: +ngbBnTRn0Mr7cLCP/JleI/4Fn0MCWxoftTvdQbaPVo02UWiAgIovfyL2rqoXm/OE0IVM3c49fpGfLAzWU9hVIe3r+NGX2HEOBPvykcwvCI7040PaILY82s7iliDaqmLTp0KBejN3NRVFovINjT6Rg== X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 7a96b45f-42f4-45ea-98b0-08d7c5008cc5 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Mar 2020 14:37:25.0825 (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: FCtmS1t5qcpfS9t9mc9TrRdDZU5C9m0HUneKlqGb2KcHakwTnZOhfWl5LAZhisfDGRMZvmwlJqQY86uxpJznfA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR12MB1606 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/6/20 11:20 AM, Connor Kuehl wrote: > Instead of using CAP_SYS_ADMIN which is restricted to the root user, > check the file mode for write permissions before executing commands that > can affect the platform. This allows for more fine-grained access > control to the SEV ioctl interface. This would allow a SEV-only user > or group the ability to administer the platform without requiring them > to be root or granting them overly powerful permissions. > > For example: > > chown root:root /dev/sev > chmod 600 /dev/sev > setfacl -m g:sev:r /dev/sev > setfacl -m g:sev-admin:rw /dev/sev > > In this instance, members of the "sev-admin" group have the ability to > perform all ioctl calls (including the ones that modify platform state). > Members of the "sev" group only have access to the ioctls that do not > modify the platform state. > > This also makes opening "/dev/sev" more consistent with how file > descriptors are usually handled. By only checking for CAP_SYS_ADMIN, > the file descriptor could be opened read-only but could still execute > ioctls that modify the platform state. This patch enforces that the file > descriptor is opened with write privileges if it is going to be used to > modify the platform state. > > This flexibility is completely opt-in, and if it is not desirable by > the administrator then they do not need to give anyone else access to > /dev/sev. > > Signed-off-by: Connor Kuehl > --- > drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++---------------- > 1 file changed, 17 insertions(+), 16 deletions(-) > Reviewed-by: Brijesh Singh thanks