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

From: Cristian Marussi
Date: Thu Jun 16 2022 - 13:04:10 EST


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.

Fixes: 7bc7caafe6b1 ("firmware: arm_scmi: Use common iterators in the clock protocol")
Signed-off-by: Cristian Marussi <cristian.marussi@xxxxxxx>
---
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;
};

--
2.32.0