[PATCH 2/2] spi: spi-zynq-qspi: Fix stack violation bug

[Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>]

From: Karen Dombroski <karen.dombroski@marsbioimaging.com>

When the number of bytes for the op is greater than one, the read could
run off the end of the function stack and cause a crash.

This patch restores the behaviour of safely reading out of the original
opcode location.

Kernel panic - not syncing: stack-protector: Kernel stack is corrupted
 in: zynq_qspi_exec_mem_op+0x1c0/0x2e0
CPU1: stopping
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.9.11-mars-2020.11 #2
Hardware name: Xilinx Zynq Platform
[<c010c15c>] (unwind_backtrace) from [<c0109034>] (show_stack+0x10/0x14)
[<c0109034>] (show_stack) from [<c0591848>] (dump_stack+0xb8/0xd4)
[<c0591848>] (dump_stack) from [<c010aecc>] (handle_IPI+0xe0/0x1a4)
[<c010aecc>] (handle_IPI) from [<c0343890>] (gic_handle_irq+0x84/0x90)
[<c0343890>] (gic_handle_irq) from [<c0100b0c>] (__irq_svc+0x6c/0xa8)
Exception stack(0xef087f58 to 0xef087fa0)
7f40:                                                       00000780 ef7e26f4
7f60: 00000000 c0114380 00000000 00000000 ef086000 c0903eec 00000002 ef087fb8
7f80: c0903f28 00000000 ffffffe8 ef087fa8 c0106824 c0106814 60000013 ffffffff
[<c0100b0c>] (__irq_svc) from [<c0106814>] (arch_cpu_idle+0x1c/0x38)
[<c0106814>] (arch_cpu_idle) from [<c0598d58>] (default_idle_call+0x20/0x28)
[<c0598d58>] (default_idle_call) from [<c013b744>] (do_idle+0x124/0x22c)
[<c013b744>] (do_idle) from [<c013b9bc>] (cpu_startup_entry+0x18/0x1c)
[<c013b9bc>] (cpu_startup_entry) from [<001014ac>] (0x1014ac)

Signed-off-by: Karen Dombroski <karen.dombroski@marsbioimaging.com>
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
---
 drivers/spi/spi-zynq-qspi.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-zynq-qspi.c b/drivers/spi/spi-zynq-qspi.c
index 1acde9e24973..5a3d81c31d04 100644
--- a/drivers/spi/spi-zynq-qspi.c
+++ b/drivers/spi/spi-zynq-qspi.c
@@ -528,18 +528,17 @@ static int zynq_qspi_exec_mem_op(struct spi_mem *mem,
        struct zynq_qspi *xqspi = spi_controller_get_devdata(mem->spi->master);
        int err = 0, i;
        u8 *tmpbuf;
-       u8 opcode = op->cmd.opcode;

        dev_dbg(xqspi->dev, "cmd:%#x mode:%d.%d.%d.%d\n",
-               opcode, op->cmd.buswidth, op->addr.buswidth,
+               op->cmd.opcode, op->cmd.buswidth, op->addr.buswidth,
                op->dummy.buswidth, op->data.buswidth);

        zynq_qspi_chipselect(mem->spi, true);
        zynq_qspi_config_op(xqspi, mem->spi);

-       if (op->cmd.nbytes) {
+       if (op->cmd.opcode) {
                reinit_completion(&xqspi->data_completion);
-               xqspi->txbuf = &opcode;
+               xqspi->txbuf = (u8 *)&op->cmd.opcode;
                xqspi->rxbuf = NULL;
                xqspi->tx_bytes = op->cmd.nbytes;
                xqspi->rx_bytes = op->cmd.nbytes;
--
2.17.1

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