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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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().
>> +     */
>> +    if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) )
>> +    {
>> +        cr4_pv32_mask &= ~X86_CR4_SMAP;
>> +        write_cr4(read_cr4() & ~X86_CR4_SMAP);
>> +    }
>> +    rc = dom0_construct(d, image, image_headroom, initrd, cmdline);
>> +    if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) )
> ... blank lines added around the function call. Happy to adjust while
> committing, so long as you agree.

+1 to both suggestions.

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>