[PATCH 5.10.y] hwmon: (coretemp) Fix 32-bit jiffies wraparound in show_temp()

[Sasha Levin <sashal@kernel.org>]

From: Guenter Roeck <linux@roeck-us.net>

[ Upstream commit 9a6aa085c94c7f2817c4d50a7264e6fb51286f40 ]

show_temp() rate-limits MSR reads by storing tdata->last_updated as an
unsigned long and comparing it against jiffies using
time_after(jiffies, tdata->last_updated + HZ).

time_after() relies on signed long subtraction, which only produces the
expected result while the two timestamps are within LONG_MAX jiffies of
each other. On 32-bit kernels, if tempX_input is not read for more than
LONG_MAX jiffies (~24.85 days at HZ=1000), the signed difference flips
sign and time_after() evaluates to false. Because tdata->last_updated is
only refreshed when time_after() succeeds, subsequent reads remain
blocked from refreshing for another ~24.85 days until jiffies wraps
past tdata->last_updated + HZ again, returning either a stale cached
temperature or -ENODATA if the sensor had never been read since
initialization.

Store tdata->last_updated as a u64 and use get_jiffies_64() with
time_after64(), which does not wrap in any practical uptime.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Fixes: bebe467823c0 ("hwmon: New coretemp driver")
Cc: stable@vger.kernel.org
Tested-by: Asaf Nuri Bertizlioğlu <ycistak@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
[ sashal: adapted the time comparison to preserve the existing !tdata->valid guard for first-read handling ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hwmon/coretemp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
index cbe2f874b5e2f..d8ab0175f16b1 100644
--- a/drivers/hwmon/coretemp.c
+++ b/drivers/hwmon/coretemp.c
@@ -70,7 +70,7 @@ struct temp_data {
 	int temp;
 	int ttarget;
 	int tjmax;
-	unsigned long last_updated;
+	u64 last_updated;
 	unsigned int cpu;
 	u32 cpu_core_id;
 	u32 status_reg;
@@ -157,7 +157,8 @@ static ssize_t show_temp(struct device *dev,
 	mutex_lock(&tdata->update_lock);
 
 	/* Check whether the time interval has elapsed */
-	if (!tdata->valid || time_after(jiffies, tdata->last_updated + HZ)) {
+	if (!tdata->valid ||
+	    time_after64(get_jiffies_64(), tdata->last_updated + HZ)) {
 		rdmsr_on_cpu(tdata->cpu, tdata->status_reg, &eax, &edx);
 		/*
 		 * Ignore the valid bit. In all observed cases the register
@@ -167,7 +168,7 @@ static ssize_t show_temp(struct device *dev,
 		 */
 		tdata->temp = tdata->tjmax - ((eax >> 16) & 0x7f) * 1000;
 		tdata->valid = 1;
-		tdata->last_updated = jiffies;
+		tdata->last_updated = get_jiffies_64();
 	}
 
 	mutex_unlock(&tdata->update_lock);
-- 
2.53.0