linux-kernel - Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

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Message-ID: <jpgpndkjmkb.fsf@linux.bootlegged.copy>
Date:   Tue, 10 Mar 2020 10:45:24 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     Connor Kuehl <ckuehl@...hat.com>, thomas.lendacky@....com,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        gary.hook@....com, erdemaktas@...gle.com, rientjes@...gle.com,
        npmccallum@...hat.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

Brijesh Singh <brijesh.singh@....com> writes:

> 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 <ckuehl@...hat.com>
>> ---
>>   drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>>   1 file changed, 17 insertions(+), 16 deletions(-)
>>
>
> Reviewed-by: Brijesh Singh <brijesh.singh@....com>
>
> thanks

Reviewed-by: Bandan Das <bsd@...hat.com>