drm/i915/cmdparser: Do not check past the cmd length.

The command MEDIA_VFE_STATE checks bits at offset +2 dwords. However, it is
possible to have MEDIA_VFE_STATE command with length = 0 + LENGTH_BIAS = 2.
In that case check_cmd will read bits from the following command, or even past
the end of the buffer.

If the offset ends up outside of the command length, reject the command.

Fixes: 351e3db2b363 ("drm/i915: Implement command buffer parsing logic")
Signed-off-by: Michal Srb <msrb@suse.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205151745.29292-1-msrb@suse.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180205160438.3267-2-chris@chris-wilson.co.uk
(cherry picked from commit 3aec7f871c65eb5f76b4125fda432593c834a6f2)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
index ab4c8b0ec886..95478db9998b 100644
--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -1212,6 +1212,12 @@ static bool check_cmd(const struct intel_engine_cs *engine,
                                         continue;
                         }
 
+                        if (desc->bits[i].offset >= length) {
+                                DRM_DEBUG_DRIVER("CMD: Rejected command 0x%08X, too short to check bitmask (%s)\n",
+                                                 *cmd, engine->name);
+                                return false;
+                        }
+
                         dword = cmd[desc->bits[i].offset] &
                                 desc->bits[i].mask;