[PATCH 2/5] drm/i915: consider vm_pgoff in vm_access()

["David Hildenbrand (Arm)" <david@kernel.org>]

vm_access() treats the start of every VMA as the beginning of the GEM
object. After a VMA split, vm_pgoff identifies a later part of the
object. Debugger reads and writes through ptrace or /proc/<pid>/mem then
access the wrong bytes.

Properly consider vm_pgoff just like the fault handlers already do.

Fixes: 9f909e215fea ("drm/i915: Implement vm_ops->access for gdb access into mmaps")
Cc: stable@vger.kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 drivers/gpu/drm/i915/gem/i915_gem_mman.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index 6b337684dbfe8..e3b24dc8e94f5 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -511,13 +511,15 @@ vm_access(struct vm_area_struct *area, unsigned long addr,
 	struct i915_mmap_offset *mmo = area->vm_private_data;
 	struct drm_i915_gem_object *obj = mmo->obj;
 	struct i915_gem_ww_ctx ww;
+	unsigned long obj_offset;
 	void *vaddr;
 	int err = 0;
 
 	if (i915_gem_object_is_readonly(obj) && write)
 		return -EACCES;
 
-	addr -= area->vm_start;
+	obj_offset = area->vm_pgoff - drm_vma_node_start(&mmo->vma_node);
+	addr += (obj_offset << PAGE_SHIFT) - area->vm_start;
 	if (range_overflows_t(u64, addr, len, obj->base.size))
 		return -EINVAL;
 

-- 
2.43.0