[PATCH v5 7/8] drm/xe/mmio_gem: reject VM_EXEC and drop VM_DONTCOPY

[Matthew Auld <matthew.auld@intel.com>]

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;
-- 
2.55.0