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

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Date:   Tue, 10 Mar 2020 12:02:05 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Bandan Das <bsd@...hat.com>
cc:     Brijesh Singh <brijesh.singh@....com>,
        Connor Kuehl <ckuehl@...hat.com>, thomas.lendacky@....com,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        gary.hook@....com, erdemaktas@...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

On Tue, 10 Mar 2020, Bandan Das wrote:

> 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>
> 

Acked-by: David Rientjes <rientjes@...gle.com>