hw/ssi/xilinx_spips: Avoid AXI writes to the LQSPI linear memory

Lei Sun found while auditing the code that a CPU write would
trigger a NULL pointer dereference.

>From UG1085 datasheet [*] AXI writes in this region are ignored
and generates an AXI Slave Error (SLVERR).

Fix by implementing the write_with_attrs() handler.
Return MEMTX_ERROR when the region is accessed (this error maps
to an AXI slave error).

[*] https://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf

Reported-by: Lei Sun <slei.casper@gmail.com>
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Tested-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/hw/ssi/xilinx_spips.c b/hw/ssi/xilinx_spips.c
index b7c7275dbe..3c4e8365ee 100644
--- a/hw/ssi/xilinx_spips.c
+++ b/hw/ssi/xilinx_spips.c
@@ -1220,8 +1220,24 @@ static MemTxResult lqspi_read(void *opaque, hwaddr addr, uint64_t *value,
     return lqspi_read(opaque, addr, value, size, attrs);
 }
 
+static MemTxResult lqspi_write(void *opaque, hwaddr offset, uint64_t value,
+                               unsigned size, MemTxAttrs attrs)
+{
+    /*
+     * From UG1085, Chapter 24 (Quad-SPI controllers):
+     * - Writes are ignored
+     * - AXI writes generate an external AXI slave error (SLVERR)
+     */
+    qemu_log_mask(LOG_GUEST_ERROR, "%s Unexpected %u-bit access to 0x%" PRIx64
+                                   " (value: 0x%" PRIx64 "\n",
+                  __func__, size << 3, offset, value);
+
+    return MEMTX_ERROR;
+}
+
 static const MemoryRegionOps lqspi_ops = {
     .read_with_attrs = lqspi_read,
+    .write_with_attrs = lqspi_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
     .valid = {
         .min_access_size = 1,