[PATCH] firmware: arm_scmi: Relax CLOCK_DESCRIBE_RATES out-of-spec checks

[Robin Murphy]

On 2022-06-16 18:03, Cristian Marussi wrote:
> A reply to CLOCK_DESCRIBE_RATES issued against a non rate-discrete clock
> should be composed of a triplet of rates descriptors (min/max/step)
> returned all in one reply message.
> 
> This is not always the case when dealing with some SCMI server deployed in
> the wild: relax such constraint while maintaining memory safety by checking
> carefully the returned payload size.
> 
> While at that cleanup a stale debug printout.

I know we're testing on the same platform so it's of limited value, but 
for the record this does indeed make my display work again, so FWIW:

Tested-by: Robin Murphy <robin.murphy at arm.com>

Thanks for the quick turnaround!
Robin.

> Fixes: 7bc7caafe6b1 ("firmware: arm_scmi: Use common iterators in the clock protocol")
> Signed-off-by: Cristian Marussi <cristian.marussi at arm.com>
> ---
>   drivers/firmware/arm_scmi/clock.c     | 26 +++++++++++++++++++++++++-
>   drivers/firmware/arm_scmi/driver.c    |  1 +
>   drivers/firmware/arm_scmi/protocols.h |  3 +++
>   3 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/arm_scmi/clock.c b/drivers/firmware/arm_scmi/clock.c
> index c7a83f6e38e5..3ed7ae0d6781 100644
> --- a/drivers/firmware/arm_scmi/clock.c
> +++ b/drivers/firmware/arm_scmi/clock.c
> @@ -194,6 +194,7 @@ static int rate_cmp_func(const void *_r1, const void *_r2)
>   }
>   
>   struct scmi_clk_ipriv {
> +	struct device *dev;
>   	u32 clk_id;
>   	struct scmi_clock_info *clk;
>   };
> @@ -223,6 +224,29 @@ iter_clk_describe_update_state(struct scmi_iterator_state *st,
>   	st->num_returned = NUM_RETURNED(flags);
>   	p->clk->rate_discrete = RATE_DISCRETE(flags);
>   
> +	/* Warn about out of spec replies ... */
> +	if (!p->clk->rate_discrete &&
> +	    (st->num_returned != 3 || st->num_remaining != 0)) {
> +		dev_warn(p->dev,
> +			 "Out-of-spec CLOCK_DESCRIBE_RATES reply for %s - returned:%d remaining:%d rx_len:%zd\n",
> +			 p->clk->name, st->num_returned, st->num_remaining,
> +			 st->rx_len);
> +
> +		/*
> +		 * A known quirk: a triplet is returned but num_returned != 3
> +		 * Check for a safe payload size and fix.
> +		 */
> +		if (st->num_returned != 3 && st->num_remaining == 0 &&
> +		    st->rx_len == sizeof(*r) + sizeof(__le32) * 2 * 3) {
> +			st->num_returned = 3;
> +			st->num_remaining = 0;
> +		} else {
> +			dev_err(p->dev,
> +				"Cannot fix out-of-spec reply !\n");
> +			return -EPROTO;
> +		}
> +	}
> +
>   	return 0;
>   }
>   
> @@ -255,7 +279,6 @@ iter_clk_describe_process_response(const struct scmi_protocol_handle *ph,
>   
>   		*rate = RATE_TO_U64(r->rate[st->loop_idx]);
>   		p->clk->list.num_rates++;
> -		//XXX dev_dbg(ph->dev, "Rate %llu Hz\n", *rate);
>   	}
>   
>   	return ret;
> @@ -275,6 +298,7 @@ scmi_clock_describe_rates_get(const struct scmi_protocol_handle *ph, u32 clk_id,
>   	struct scmi_clk_ipriv cpriv = {
>   		.clk_id = clk_id,
>   		.clk = clk,
> +		.dev = ph->dev,
>   	};
>   
>   	iter = ph->hops->iter_response_init(ph, &ops, SCMI_MAX_NUM_RATES,
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index c1922bd650ae..8b7ac6663d57 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -1223,6 +1223,7 @@ static int scmi_iterator_run(void *iter)
>   		if (ret)
>   			break;
>   
> +		st->rx_len = i->t->rx.len;
>   		ret = iops->update_state(st, i->resp, i->priv);
>   		if (ret)
>   			break;
> diff --git a/drivers/firmware/arm_scmi/protocols.h b/drivers/firmware/arm_scmi/protocols.h
> index c679f3fb8718..51c31379f9b3 100644
> --- a/drivers/firmware/arm_scmi/protocols.h
> +++ b/drivers/firmware/arm_scmi/protocols.h
> @@ -179,6 +179,8 @@ struct scmi_protocol_handle {
>    * @max_resources: Maximum acceptable number of items, configured by the caller
>    *		   depending on the underlying resources that it is querying.
>    * @loop_idx: The iterator loop index in the current multi-part reply.
> + * @rx_len: Size in bytes of the currenly processed message; it can be used by
> + *	    the user of the iterator to verify a reply size.
>    * @priv: Optional pointer to some additional state-related private data setup
>    *	  by the caller during the iterations.
>    */
> @@ -188,6 +190,7 @@ struct scmi_iterator_state {
>   	unsigned int num_remaining;
>   	unsigned int max_resources;
>   	unsigned int loop_idx;
> +	size_t rx_len;
>   	void *priv;
>   };
>