Re: [PATCH v4 7/8] drm/xe/mmio_gem: reject VM_EXEC and drop VM_DONTCOPY

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 9/8/26 15:50, Matthew Auld wrote:
> Hardware MMIO registers should never be executable; reject VM_EXEC
> at mmap time and clear VM_MAYEXEC to prevent later mprotect attempts.
>
> Also drop VM_DONTCOPY so that child processes across fork() can
> inherit the mapping and lazily fault in the PFNs, matching standard
> DRM GEM semantics and making the existing drm_gem_vm_open() callback
> functional.
>
> This aligns with existing PCI_BARRIER, which will use this in the next
> patch. We don't want any noticeable behaviour change there, since this
> will be user visible. This will also be the first user.
>
> Assisted-by: LLM
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Tejas Upadhyay <tejas.upadhyay@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Ilia Levi <ilia.levi@intel.com>

Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>



> ---
>   drivers/gpu/drm/xe/xe_mmio_gem.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_mmio_gem.c b/drivers/gpu/drm/xe/xe_mmio_gem.c
> index 5ffe03d36190..3cdc9538957d 100644
> --- a/drivers/gpu/drm/xe/xe_mmio_gem.c
> +++ b/drivers/gpu/drm/xe/xe_mmio_gem.c
> @@ -177,9 +177,12 @@ static int xe_mmio_gem_mmap(struct drm_gem_object *base, struct vm_area_struct *
>   	if ((vma->vm_flags & VM_SHARED) == 0)
>   		return -EINVAL;
>   
> +	if (vma->vm_flags & VM_EXEC)
> +		return -EINVAL;
> +
>   	vma->vm_page_prot = pgprot_noncached(vma_get_page_prot(vma));
> -	vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP |
> -		     VM_DONTCOPY | VM_NORESERVE);
> +	vm_flags_mod(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP |
> +		     VM_NORESERVE, VM_MAYEXEC);
>   
>   	/* Defer actual mapping to the fault handler. */
>   	return 0;