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


From: Cédric Le Goater
Subject: Re: [PATCH v2 3/4] m25p80: Improve command handling for unsupported commands
Date: Fri, 7 Feb 2020 08:22:30 +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>


Reviewed-by: Cédric Le Goater <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;
>          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;
>      }
> 




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