linux-kernel - [PATCH AUTOSEL 4.18 75/76] firmware: arm_scmi: fix divide by zero when sustained_perf

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Date:   Mon, 24 Sep 2018 14:48:45 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Sudeep Holla <sudeep.holla@....com>,
        Olof Johansson <olof@...om.net>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 75/76] firmware: arm_scmi: fix divide by zero
 when sustained_perf_level is zero

From: Sudeep Holla <sudeep.holla@....com>

[ Upstream commit 96d529bac562574600eda85726fcfa3eef6dde8e ]

Firmware can provide zero as values for sustained performance level and
corresponding sustained frequency in kHz in order to hide the actual
frequencies and provide only abstract values. It may endup with divide
by zero scenario resulting in kernel panic.

Let's set the multiplication factor to one if either one or both of them
(sustained_perf_level and sustained_freq) are set to zero.

Fixes: a9e3fbfaa0ff ("firmware: arm_scmi: add initial support for performance protocol")
Reported-by: Ionela Voinescu <ionela.voinescu@....com>
Signed-off-by: Sudeep Holla <sudeep.holla@....com>
Signed-off-by: Olof Johansson <olof@...om.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/firmware/arm_scmi/perf.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
index 2a219b1261b1..49cb74f54a10 100644
--- a/drivers/firmware/arm_scmi/perf.c
+++ b/drivers/firmware/arm_scmi/perf.c
@@ -166,7 +166,13 @@ scmi_perf_domain_attributes_get(const struct scmi_handle *handle, u32 domain,
 					le32_to_cpu(attr->sustained_freq_khz);
 		dom_info->sustained_perf_level =
 					le32_to_cpu(attr->sustained_perf_level);
-		dom_info->mult_factor =	(dom_info->sustained_freq_khz * 1000) /
+		if (!dom_info->sustained_freq_khz ||
+		    !dom_info->sustained_perf_level)
+			/* CPUFreq converts to kHz, hence default 1000 */
+			dom_info->mult_factor =	1000;
+		else
+			dom_info->mult_factor =
+					(dom_info->sustained_freq_khz * 1000) /
 					dom_info->sustained_perf_level;
 		memcpy(dom_info->name, attr->name, SCMI_MAX_STR_SIZE);
 	}
-- 
2.17.1