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Re: [PATCH v2 3/4] m25p80: Improve command handling for unsupported comm

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 3/4] m25p80: Improve command handling for unsupported commands
Date: Fri, 7 Feb 2020 01:21:12 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 2/6/20 7:32 PM, Guenter Roeck wrote:
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 <address@hidden>
v2: Split patch into two parts; improved description.

  hw/block/m25p80.c | 5 +++++
  1 file changed, 5 insertions(+)

diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
index 53bf63856f..8227088441 100644
--- 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;
+        s->pos = 0;
+        s->len = 1;
+        s->state = STATE_READING_DATA;
+        s->data_read_loop = true;
+        s->data[0] = 0;

Maybe self-explicit using:

           s->data[0] = NOP;

Matter of taste probably, but I find this order easier to review:

           s->state = STATE_READING_DATA;
           s->data_read_loop = true;
           s->pos = 0;
           s->data[0] = NOP;
           s->len = 1;

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

          qemu_log_mask(LOG_GUEST_ERROR, "M25P80: Unknown cmd %x\n", value);

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