[PATCH] firmware: imx: warn on unexpected RX

[Leonard Crestez <leonard.crestez@nxp.com>]

The imx_scu_call_rpc function function returns the result inside the
same "msg" struct containing the transmitted message. This is
implemented by holding a pointer to msg (which is usually on the stack)
in sc_imx_rpc and writing to it from imx_scu_rx_callback.

This means that if the have_resp parameter is incorrect or SCU sends an
unexpected for any reason the most likely result is kernel stack
corruption.

Fix this by only setting sc_imx_rpc.msg for the duration of the
imx_scu_call_rpc call and warning in imx_scu_rx_callback if unset.

Print the unexpected response data to help debugging.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
---
 drivers/firmware/imx/imx-scu.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/imx/imx-scu.c b/drivers/firmware/imx/imx-scu.c
index 04a24a863d6e..869be7a5172c 100644
--- a/drivers/firmware/imx/imx-scu.c
+++ b/drivers/firmware/imx/imx-scu.c
@@ -105,10 +105,16 @@ static void imx_scu_rx_callback(struct mbox_client *c, void *msg)
 	struct imx_sc_chan *sc_chan = container_of(c, struct imx_sc_chan, cl);
 	struct imx_sc_ipc *sc_ipc = sc_chan->sc_ipc;
 	struct imx_sc_rpc_msg *hdr;
 	u32 *data = msg;
 
+	if (!sc_ipc->msg) {
+		dev_warn(sc_ipc->dev, "unexpected rx idx %d 0x%08x, ignore!\n",
+				sc_chan->idx, *data);
+		return;
+	}
+
 	if (sc_chan->idx == 0) {
 		hdr = msg;
 		sc_ipc->rx_size = hdr->size;
 		dev_dbg(sc_ipc->dev, "msg rx size %u\n", sc_ipc->rx_size);
 		if (sc_ipc->rx_size > 4)
@@ -163,11 +169,12 @@ int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
 		return -EINVAL;
 
 	mutex_lock(&sc_ipc->lock);
 	reinit_completion(&sc_ipc->done);
 
-	sc_ipc->msg = msg;
+	if (have_resp)
+		sc_ipc->msg = msg;
 	sc_ipc->count = 0;
 	ret = imx_scu_ipc_write(sc_ipc, msg);
 	if (ret < 0) {
 		dev_err(sc_ipc->dev, "RPC send msg failed: %d\n", ret);
 		goto out;
@@ -185,10 +192,11 @@ int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
 		hdr = msg;
 		ret = hdr->func;
 	}
 
 out:
+	sc_ipc->msg = NULL;
 	mutex_unlock(&sc_ipc->lock);
 
 	dev_dbg(sc_ipc->dev, "RPC SVC done\n");
 
 	return imx_sc_to_linux_errno(ret);
-- 
2.17.1


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