[PATCH] spi: zynq-qspi: fix address buffer corruption and support 4-byte address

[Pufan Jin]

In zynq_qspi_exec_mem_op(), when transmitting address bytes, the driver
iterates over op->addr.nbytes and populates xqspi->txbuf[i]. However,
xqspi->txbuf is never re-assigned before populating the address, meaning
it still points to (u8 *)&op->cmd.opcode from the command phase.

This causes two severe issues:
1. Memory corruption: Writing into xqspi->txbuf writes past the opcode
   buffer on the stack (which was passed as const struct spi_mem_op *).
   If opcode is zero, xqspi->txbuf is uninitialized.
2. In zynq_qspi_supports_op(), operations with op->addr.nbytes > 3 are
   rejected. When paired with SPI NOR flashes larger than 16MB (such as
   Winbond W25Q256), spi_nor_spimem_check_read_pp_op() tests 4-byte address
   support, which fails and causes spi_nor_select_read() to drop all read
   capabilities, failing probe with -EINVAL (-22).

The Zynq-7000 QSPI controller hardware in manual I/O mode natively supports
transmitting 1 to 4 address bytes via its TXD FIFO registers
(ZYNQ_QSPI_TXD_00_00_OFFSET).

Fix this by introducing a local opaddr[4] buffer in zynq_qspi_exec_mem_op()
and explicitly setting xqspi->txbuf = opaddr before populating address
bytes. Also allow up to 4 address bytes in zynq_qspi_supports_op().

Fixes: 67dca5e580f1 ("spi: spi-mem: Add support for Zynq QSPI controller")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Pufan Jin <cyan2254650260@xxxxxxxxx>
---
 drivers/spi/spi-zynq-qspi.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi-zynq-qspi.c b/drivers/spi/spi-zynq-qspi.c
index d762aaf45..bfcbcfe85 100644
--- a/drivers/spi/spi-zynq-qspi.c
+++ b/drivers/spi/spi-zynq-qspi.c
@@ -229,11 +229,10 @@ static bool zynq_qspi_supports_op(struct spi_mem *mem,
 		return false;
 
 	/*
-	 * The number of address bytes should be equal to or less than 3 bytes.
+	 * The number of address bytes should be equal to or less than 4 bytes.
 	 */
-	if (op->addr.nbytes > 3)
+	if (op->addr.nbytes > 4)
 		return false;
-
 	return true;
 }
 
@@ -526,6 +525,7 @@ static int zynq_qspi_exec_mem_op(struct spi_mem *mem,
 				 const struct spi_mem_op *op)
 {
 	struct zynq_qspi *xqspi = spi_controller_get_devdata(mem->spi->controller);
+	u8 opaddr[4] __aligned(4);
 	int err = 0, i;
 	u8 *tmpbuf;
 
@@ -547,12 +547,13 @@ static int zynq_qspi_exec_mem_op(struct spi_mem *mem,
 	}
 
 	if (op->addr.nbytes) {
-		for (i = 0; i < op->addr.nbytes; i++) {
-			xqspi->txbuf[i] = op->addr.val >>
+		for (i = 0; i < op->addr.nbytes; i++)
+			opaddr[i] = op->addr.val >>
 					(8 * (op->addr.nbytes - i - 1));
-		}
 
 		reinit_completion(&xqspi->data_completion);
+		xqspi->txbuf = opaddr;
+
 		xqspi->rxbuf = NULL;
 		xqspi->tx_bytes = op->addr.nbytes;
 		xqspi->rx_bytes = op->addr.nbytes;
-- 
2.56.0