[PATCH] accel/rocket: Validate task regcmd address and count on submission

[Sidong Yang]

The regcmd fields in drm_rocket_task come from userspace and are
programmed into the PC unit without any validation.

Bits 31:4 of PC_BASE_ADDRESS hold the register command DMA address
and bit 0 selects slave mode, so a misaligned regcmd silently drops
its low bits, and an odd address flips the PC unit into slave mode.
Similarly, pc_data_amount is a 16-bit field holding
(regcmd_count + 1) / 2 - 1, so a larger regcmd_count is silently
truncated by the register encoding.

Reject unaligned regcmd addresses and out-of-range regcmd_count with
-EINVAL at submission time. Existing userspace is not affected: Mesa
places regcmd buffers at 64-byte aligned offsets, and its regcmd
counts stay far below the limit.

Signed-off-by: Sidong Yang <sidong.yang@xxxxxxxxxx>
---
 drivers/accel/rocket/rocket_job.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/accel/rocket/rocket_job.c b/drivers/accel/rocket/rocket_job.c
index bb77b6bf0f23..9ebabf86fe97 100644
--- a/drivers/accel/rocket/rocket_job.c
+++ b/drivers/accel/rocket/rocket_job.c
@@ -7,6 +7,7 @@
 #include <drm/drm_file.h>
 #include <drm/drm_gem.h>
 #include <drm/rocket_accel.h>
+#include <linux/align.h>
 #include <linux/interrupt.h>
 #include <linux/overflow.h>
 #include <linux/iommu.h>
@@ -21,6 +22,15 @@
 
 #define JOB_TIMEOUT_MS 500
 
+/*
+ * The PC unit fetches two 64-bit register commands per pc_data_amount unit,
+ * and the field holds (regcmd_count + 1) / 2 - 1.
+ */
+#define ROCKET_MAX_REGCMDS	((PC_REGISTER_AMOUNTS_PC_DATA_AMOUNT__MASK + 1) * 2U)
+
+/* Bits 3:0 of PC_BASE_ADDRESS hold the mode selection bit and reserved bits */
+#define ROCKET_REGCMD_ALIGN	16
+
 static struct rocket_job *
 to_rocket_job(struct drm_sched_job *sched_job)
 {
@@ -95,6 +105,20 @@ rocket_copy_tasks(struct drm_device *dev,
 			goto fail;
 		}
 
+		if (task.regcmd_count > ROCKET_MAX_REGCMDS) {
+			drm_dbg(dev, "regcmd_count field in drm_rocket_task should be <= %u.\n",
+				ROCKET_MAX_REGCMDS);
+			ret = -EINVAL;
+			goto fail;
+		}
+
+		if (!IS_ALIGNED(task.regcmd, ROCKET_REGCMD_ALIGN)) {
+			drm_dbg(dev, "regcmd field in drm_rocket_task should be aligned to %u bytes.\n",
+				ROCKET_REGCMD_ALIGN);
+			ret = -EINVAL;
+			goto fail;
+		}
+
 		rjob->tasks[i].regcmd = task.regcmd;
 		rjob->tasks[i].regcmd_count = task.regcmd_count;
 	}

base-commit: a284476db2653ae893f46cbea408eb412db54eb0
-- 
2.42.0