[PATCH AUTOSEL 6.1 09/31] cpuidle: Avoid potential overflow in integer multiplication

[Sasha Levin]

From: C Cheng <C.Cheng at mediatek.com>

[ Upstream commit 88390dd788db485912ee7f9a8d3d56fc5265d52f ]

In detail:

In C language, when you perform a multiplication operation, if
both operands are of int type, the multiplication operation is
performed on the int type, and then the result is converted to
the target type. This means that if the product of int type
multiplication exceeds the range that int type can represent,
an overflow will occur even if you store the result in a
variable of int64_t type.

For a multiplication of two int values, it is better to use
mul_u32_u32() rather than s->exit_latency_ns = s->exit_latency *
NSEC_PER_USEC to avoid potential overflow happenning.

Signed-off-by: C Cheng <C.Cheng at mediatek.com>
Signed-off-by: Bo Ye <bo.ye at mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
[ rjw: New subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/cpuidle/driver.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index f70aa17e2a8e0..c594e28adddf3 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c
@@ -16,6 +16,7 @@
 #include <linux/cpumask.h>
 #include <linux/tick.h>
 #include <linux/cpu.h>
+#include <linux/math64.h>
 
 #include "cpuidle.h"
 
@@ -185,7 +186,7 @@ static void __cpuidle_driver_init(struct cpuidle_driver *drv)
 			s->target_residency_ns = 0;
 
 		if (s->exit_latency > 0)
-			s->exit_latency_ns = s->exit_latency * NSEC_PER_USEC;
+			s->exit_latency_ns = mul_u32_u32(s->exit_latency, NSEC_PER_USEC);
 		else if (s->exit_latency_ns < 0)
 			s->exit_latency_ns =  0;
 	}
-- 
2.43.0