drm/i915: Large page offsets for pread/pwrite

Handle integer overflow when computing the sub-page length for shmem
backed pread/pwrite.

Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181012140228.29783-1-chris@chris-wilson.co.uk
(cherry picked from commit a5e856a5348f6cd50889d125c40bbeec7328e466)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

1 files changed, 2 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index db9688d14912..aa3969d52773 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1127,11 +1127,7 @@ i915_gem_shmem_pread(struct drm_i915_gem_object *obj,
         offset = offset_in_page(args->offset);
         for (idx = args->offset >> PAGE_SHIFT; remain; idx++) {
                 struct page *page = i915_gem_object_get_page(obj, idx);
-                int length;
-
-                length = remain;
-                if (offset + length > PAGE_SIZE)
-                        length = PAGE_SIZE - offset;
+                unsigned int length = min_t(u64, remain, PAGE_SIZE - offset);
 
                 ret = shmem_pread(page, offset, length, user_data,
                                   page_to_phys(page) & obj_do_bit17_swizzling,
@@ -1575,11 +1571,7 @@ i915_gem_shmem_pwrite(struct drm_i915_gem_object *obj,
         offset = offset_in_page(args->offset);
         for (idx = args->offset >> PAGE_SHIFT; remain; idx++) {
                 struct page *page = i915_gem_object_get_page(obj, idx);
-                int length;
-
-                length = remain;
-                if (offset + length > PAGE_SIZE)
-                        length = PAGE_SIZE - offset;
+                unsigned int length = min_t(u64, remain, PAGE_SIZE - offset);
 
                 ret = shmem_pwrite(page, offset, length, user_data,
                                    page_to_phys(page) & obj_do_bit17_swizzling,