[PATCH 2/2] firmware: zynqmp: fix write to an uninitialised pointer in ipi_req()

[Michal Simek]

When a caller is not interested in the returned message, the ret_payload
pointer is set to NULL in the u-boot-sources. In this case, under EL3, the
memory from address 0x0 would be overwritten by ipi_req() with the returned
IPI message, damaging the original data under this address. The patch, in
case ret_payload is NULL, assigns the pointer to the array holding the IPI
message being sent.

Signed-off-by: Adrian Fiergolski <adrian.fiergolski at fastree3d.com>
Signed-off-by: Michal Simek <michal.simek at xilinx.com>
---

Based on origin series from Adrian. That's why also adding his SoB line.
https://lore.kernel.org/r/20211014124349.1429696-1-adrian.fiergolski@fastree3d.com

Adrian: The patch is just suggestion how we could avoid that NULL pointer
writes but done in ipi_req()

---
 drivers/firmware/firmware-zynqmp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/firmware/firmware-zynqmp.c b/drivers/firmware/firmware-zynqmp.c
index 1391aab0a160..7e498d8169e8 100644
--- a/drivers/firmware/firmware-zynqmp.c
+++ b/drivers/firmware/firmware-zynqmp.c
@@ -30,6 +30,10 @@ static int ipi_req(const u32 *req, size_t req_len, u32 *res, size_t res_maxlen)
 {
 	struct zynqmp_ipi_msg msg;
 	int ret;
+	u32 buffer[PAYLOAD_ARG_CNT];
+
+	if (!res)
+		res = buffer;
 
 	if (req_len > PMUFW_PAYLOAD_ARG_CNT ||
 	    res_maxlen > PMUFW_PAYLOAD_ARG_CNT)
-- 
2.33.1