[PATCH] accel/ethosu: reject DMA commands with uninitialized length

[Muhammad Bilal <meatuni001@gmail.com>]

cmd_state_init() initializes the command state with memset(0xff),
leaving dma->len at U64_MAX to signal missing setup. The only setter
is NPU_SET_DMA0_LEN; if userspace omits this command and issues
NPU_OP_DMA_START, dma->len remains U64_MAX.

In dma_length(), a positive stride added to U64_MAX wraps to a small
value. With size0 == 1, check_mul_overflow() does not trigger and
dma_length() returns 0 instead of U64_MAX. The caller's U64_MAX check
then passes, region_size[] stays 0, and the bounds check in
ethosu_job.c is bypassed, allowing hardware to execute DMA with stale
physical addresses.

Fix by checking for U64_MAX at the start of dma_length() before any
arithmetic, consistent with the sentinel value used throughout the
driver to detect uninitialized fields.

Fixes: 5a5e9c0228e6 ("accel: Add Arm Ethos-U NPU driver")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
---
 drivers/accel/ethosu/ethosu_gem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/accel/ethosu/ethosu_gem.c b/drivers/accel/ethosu/ethosu_gem.c
index 8e95539da98f..3401883e207f 100644
--- a/drivers/accel/ethosu/ethosu_gem.c
+++ b/drivers/accel/ethosu/ethosu_gem.c
@@ -164,6 +164,9 @@ static u64 dma_length(struct ethosu_validated_cmdstream_info *info,
 	s8 mode = dma_st->mode;
 	u64 len = dma->len;
 
+	if (len == U64_MAX)
+		return U64_MAX;
+
 	if (mode >= 1) {
 		if (dma->stride[0] < 0 && (u64)(-dma->stride[0]) > len)
 			return U64_MAX;
-- 
2.53.0