This is a note to let you know that I've just added the patch titled
cpuidle: Avoid potential overflow in integer multiplication
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cpuidle-avoid-potential-overflow-in-integer-multipli.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit dcbddb346a78526ad4ea2b8add060fe0e96d41f5
Author: C Cheng <C.Cheng@xxxxxxxxxxxx>
Date: Tue Dec 19 11:14:42 2023 +0800
cpuidle: Avoid potential overflow in integer multiplication
[ 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@xxxxxxxxxxxx>
Signed-off-by: Bo Ye <bo.ye@xxxxxxxxxxxx>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
[ rjw: New subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index d9cda7f6ccb98..cf5873cc45dc8 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"
@@ -187,7 +188,7 @@ static void __cpuidle_driver_init(struct cpuidle_driver *drv)
s->target_residency = div_u64(s->target_residency_ns, NSEC_PER_USEC);
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;
else
