Re: [Xen-devel] [PATCH 2/2] x86/altp2m: Add a hvmop for setting the suppress #VE bit

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.06.17 at 14:04, <apop@xxxxxxxxxxxxxxx> wrote:
> On Fri, Jun 16, 2017 at 02:39:10AM -0600, Jan Beulich wrote:
>> >>> On 15.06.17 at 21:01, <tamas@xxxxxxxxxxxxx> wrote:
>> > On Fri, Jun 9, 2017 at 10:51 AM, Adrian Pop <apop@xxxxxxxxxxxxxxx> wrote:
>> >> --- a/xen/arch/x86/mm/mem_access.c
>> >> +++ b/xen/arch/x86/mm/mem_access.c
>> >> @@ -466,6 +466,58 @@ int p2m_get_mem_access(struct domain *d, gfn_t gfn, 
> xenmem_access_t *access)
>> >>  }
>> >>
>> >>  /*
>> >> + * Set/clear the #VE suppress bit for a page.  Only available on VMX.
>> >> + */
>> >> +int p2m_set_suppress_ve(struct domain *d, gfn_t gfn, bool suppress_ve,
>> >> +                        unsigned int altp2m_idx)
>> >> +{
>> >> +    struct p2m_domain *host_p2m = p2m_get_hostp2m(d);
>> >> +    struct p2m_domain *ap2m = NULL;
>> >> +    struct p2m_domain *p2m;
>> >> +    mfn_t mfn;
>> >> +    p2m_access_t a;
>> >> +    p2m_type_t t;
>> >> +    int rc;
>> >> +
>> >> +    if ( !cpu_has_vmx_virt_exceptions )
>> >> +        return -EOPNOTSUPP;
>> >> +
>> >> +    /* This subop should only be used from a privileged domain. */
>> >> +    if ( !current->domain->is_privileged )
>> >> +        return -EINVAL;
>> > 
>> > This check looks wrong to me. If this subop should only be used by an
>> > external (privileged) domain then I don't think this should be
>> > implemented as an HVMOP, looks more like a domctl to me.
>> 
>> I think this wants to be an XSM_DM_PRIV check instead.
> 
> I'm not sure, but I expect that to not behave as intended security-wise
> if Xen is compiled without XSM.  Would it?  It would be great if this
> feature worked well without XSM too.

Well, without you explaining why you think this wouldn't work
without XSM, I don't really know what to answer. I suppose
you've grep-ed for other uses of this and/or other XSM_* values,
finding that these exist in various places where all is fine without
XSM?

Jan


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