firmware: arm_scmi: Harden shared memory access in fetch_response

A misbheaving SCMI platform firmware could reply with out-of-spec messages, shorter than the mimimum size comprising a header and a status field. Harden shmem_fetch_response to properly truncate such a bad messages. Fixes: 5c8a47a ("firmware: arm_scmi: Make scmi core independent of the transport type") Signed-off-by: Cristian Marussi <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Sudeep Holla <[email protected]>
kawasaki · Jan 3, 2023 · ad78b81 · ad78b81
1 parent f6ca505
commit ad78b81
Showing 1 changed file with 3 additions and 2 deletions.
diff --git a/drivers/firmware/arm_scmi/shmem.c b/drivers/firmware/arm_scmi/shmem.c
@@ -81,10 +81,11 @@ u32 shmem_read_header(struct scmi_shared_mem __iomem *shmem)
 void shmem_fetch_response(struct scmi_shared_mem __iomem *shmem,
 			  struct scmi_xfer *xfer)
 {
+	size_t len = ioread32(&shmem->length);
+
 	xfer->hdr.status = ioread32(shmem->msg_payload);
 	/* Skip the length of header and status in shmem area i.e 8 bytes */
-	xfer->rx.len = min_t(size_t, xfer->rx.len,
-			     ioread32(&shmem->length) - 8);
+	xfer->rx.len = min_t(size_t, xfer->rx.len, len > 8 ? len - 8 : 0);
 
 	/* Take a copy to the rx buffer.. */
 	memcpy_fromio(xfer->rx.buf, shmem->msg_payload + 4, xfer->rx.len);