Patch "cpuidle: Avoid potential overflow in integer multiplication" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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 5.15-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-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 72a07253f065977f577587fa1257e4c5ff930701
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 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;
 	}