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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan