m25p80: Improve command handling for unsupported commands

Whenever an unsupported command is encountered, the current code
interprets each transferred byte as new command. Most of the time, those
'commands' are interpreted as new unknown commands. However, in rare
cases, it may be that for example address or length information
passed with the original command is by itself a valid command.
If that happens, the state machine may get completely confused and,
worst case, start writing data into the flash or even erase it.

To avoid the problem, transition into STATE_READING_DATA and keep
sending a value of 0 until the chip is deselected after encountering
an unsupported command.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
index 53bf63856f55469b5e4e4feeee4f06c2bfd7a415..82270884416e337221833bc543404e2749ff2f85 100644 (file)
--- a/hw/block/m25p80.c
+++ b/hw/block/m25p80.c
@@ -1161,6 +1161,11 @@ static void decode_new_cmd(Flash *s, uint32_t value)
         s->quad_enable = false;
         break;
     default:
+        s->pos = 0;
+        s->len = 1;
+        s->state = STATE_READING_DATA;
+        s->data_read_loop = true;
+        s->data[0] = 0;
         qemu_log_mask(LOG_GUEST_ERROR, "M25P80: Unknown cmd %x\n", value);
         break;
     }