Re: [Qemu-devel] [PATCH v1 1/1] cadence_uart: Check baud rate generator and divider values on migration

[Peter Maydell]

On 5 November 2016 at 00:00, Alistair Francis
<address@hidden> wrote:
> The Cadence UART device emulator calculates speed by dividing the
> baud rate by a 'baud rate generator' & 'baud rate divider' value.
> The device specification defines these register values to be
> non-zero and within certain limits. Checks were recently added when
> writing to these registers but not when restoring from migration.
>
> This patch adds checks when restoring from migration to avoid divide by
> zero errors.
>
> Reported-by: Huawei PSIRT <address@hidden>
> Signed-off-by: Alistair Francis <address@hidden>
> ---
>
>  hw/char/cadence_uart.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
> index def34cd..e3a6248 100644
> --- a/hw/char/cadence_uart.c
> +++ b/hw/char/cadence_uart.c
> @@ -487,6 +487,19 @@ static int cadence_uart_post_load(void *opaque, int 
> version_id)
>  {
>      CadenceUARTState *s = opaque;
>
> +    /* Ensure these two aren't invalid numbers */
> +    if (s->r[R_BRGR] <= 1) {
> +        /* Value is invalid, reset it */
> +        s->r[R_BRGR] = 0x0000028B;
> +    }
> +    if (s->r[R_BDIV] <= 3) {
> +        /* Value is invalid, reset it */
> +        s->r[R_BDIV] = 0x0000000F;
> +    }
> +
> +    s->r[R_BRGR] = s->r[R_BRGR] & 0xFFFF;
> +    s->r[R_BDIV] = s->r[R_BDIV] & 0xFF;
> +
>      uart_parameters_setup(s);
>      uart_update_status(s);
>      return 0;


Usually we just fail the migration if the incoming
data is bogus -- any particular reason not to take that
approach here?

thanks
-- PMM