Re: [Xen-devel] [PATCH v2] Merge IS_PRIV checks into XSM hooks

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 09/11/2012 04:09 AM, Jan Beulich wrote:
>>>> On 10.09.12 at 23:10, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>> On 09/10/2012 04:51 PM, Keir Fraser wrote:
>>> On 10/09/2012 20:48, "Daniel De Graaf" <dgdegra@xxxxxxxxxxxxx> wrote:
>>>
>>>> Overall, this series should not change the behavior of Xen when XSM is
>>>> not enabled; however, in some cases, the exact errors that are returned
>>>> will be different because security checks have been moved below validity
>>>> checks. Also, once applied, newly introduced domctls and sysctls will
>>>> not automatically be guarded by IS_PRIV checks - they will need to add
>>>> their own permission checking code.
>>>
>>> How do we guard against accidentally forgetting to do this?
>>
>> The same way you guard against it when adding a new hypercall: when adding
>> new functionality that needs access checks, also add the access checks.
> 
> Except that previously the access check was done centrally at the
> top of do_domctl(), so newly added sub-functions didn't need to
> worry.
> 
> Jan
> 

One addition I am considering is an extra XSM hook at the start of do_domctl
and do_sysctl that takes only the command (and domain, for domctl); this
could be used to restrict access to unknown domctl/sysctls, and would fix
the issues of adding sub-functions without access checks.

-- 
Daniel De Graaf
National Security Agency

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