drm/i915: Fix command parser to validate multiple register access with the same command.
Until now the software command checker assumed that commands could
read or write at most a single register per packet. This is not
necessarily the case, MI_LOAD_REGISTER_IMM expects a variable-length
list of offset/value pairs and writes them in sequence. The previous
code would only check whether the first entry was valid, effectively
allowing userspace to write unrestricted registers of the MMIO space
by sending a multi-register write with a legal first register, with
potential security implications on Gen6 and 7 hardware.
Fix it by extending the drm_i915_cmd_descriptor table to represent
multi-register access and making validate_cmd() iterate for all
register offsets present in the command packet.
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 46722f8..971fc33 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2312,10 +2312,15 @@
* Describes where to find a register address in the command to check
* against the ring's register whitelist. Only valid if flags has the
* CMD_DESC_REGISTER bit set.
+ *
+ * A non-zero step value implies that the command may access multiple
+ * registers in sequence (e.g. LRI), in that case step gives the
+ * distance in dwords between individual offset fields.
*/
struct {
u32 offset;
u32 mask;
+ u32 step;
} reg;
#define MAX_CMD_DESC_BITMASKS 3