Re: [PATCH v6] x86/dom0: disable SMAP for PV domain building only

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/08/2024 2:02 pm, Roger Pau Monné wrote:
> On Wed, Aug 28, 2024 at 12:51:23PM +0100, Andrew Cooper wrote:
>> On 28/08/2024 12:50 pm, Jan Beulich wrote:
>>> On 28.08.2024 13:30, Roger Pau Monne wrote:
>>>> Move the logic that disables SMAP so it's only performed when building a PV
>>>> dom0, PVH dom0 builder doesn't require disabling SMAP.
>>>>
>>>> The fixes tag is to account for the wrong usage of cpu_has_smap in
>>>> create_dom0(), it should instead have used
>>>> boot_cpu_has(X86_FEATURE_XEN_SMAP).  Fix while moving the logic to apply 
>>>> to PV
>>>> only.
>>>>
>>>> While there also make cr4_pv32_mask __ro_after_init.
>>>>
>>>> Fixes: 493ab190e5b1 ('xen/sm{e, a}p: allow disabling sm{e, a}p for Xen 
>>>> itself')
>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> preferably with ...
>>>
>>>> @@ -1051,6 +1051,34 @@ out:
>>>>      return rc;
>>>>  }
>>>>  
>>>> +int __init dom0_construct_pv(struct domain *d,
>>>> +                             const module_t *image,
>>>> +                             unsigned long image_headroom,
>>>> +                             module_t *initrd,
>>>> +                             const char *cmdline)
>>>> +{
>>>> +    int rc;
>>>> +
>>>> +    /*
>>>> +     * Temporarily clear SMAP in CR4 to allow user-accesses in
>>>> +     * construct_dom0().  This saves a large number of corner cases
>>> ... the final 's' dropped here and ...
>>>
>>>> +     * interactions with copy_from_user().


Actually, even with this adjustment the comment is still wonky.

The point is that we're clearing SMAP so we *don't* need to rewrite
construct_dom0() in terms of copy_{to,from}_user().

I've adjusted it.

~Andrew