[Intel-gfx] [PATCH 1/2] drm/i915/ttm: fix uaf with lmem_userfault_list handling

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

In the fault handler, make sure we check if the BO maps lmem after
we schedule the migration, since the current resource might change from
lmem to smem, if the pages are in the non-cpu visible portion of lmem.
This then leads to adding the object to the lmem_userfault_list even
though the current resource is no longer lmem. If we then destroy the
object, the list might still contain a link to the now free object, since
we only remove it if the object is still in lmem.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7469
Fixes: ad74457a6b5a ("drm/i915/dgfx: Release mmap on rpm suspend")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index 25129af70f70..9421dc4dc98f 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -1048,9 +1048,6 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 	}
 
-	if (i915_ttm_cpu_maps_iomem(bo->resource))
-		wakeref = intel_runtime_pm_get(&to_i915(obj->base.dev)->runtime_pm);
-
 	if (!i915_ttm_resource_mappable(bo->resource)) {
 		int err = -ENODEV;
 		int i;
@@ -1078,6 +1075,9 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
 		}
 	}
 
+	if (i915_ttm_cpu_maps_iomem(bo->resource))
+		wakeref = intel_runtime_pm_get(&to_i915(obj->base.dev)->runtime_pm);
+
 	if (drm_dev_enter(dev, &idx)) {
 		ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
 					       TTM_BO_VM_NUM_PREFAULT);
-- 
2.38.1