drm/msm: Avoid potential overflow in timeout_to_jiffies()

The return type of ktime_divns() is s64. The timeout_to_jiffies() currently
assigns the result of this ktime_divns() to unsigned long, which on 32 bit
systems may overflow. Furthermore, the result of this function is sometimes
also passed to functions which expect signed long, dma_fence_wait_timeout()
is one such example.

Fix this by adjusting the type of remaining_jiffies to s64, so we do not
suffer overflow there, and return a value limited to range of 0..INT_MAX,
which is safe for all usecases of this timeout.

The above overflow can be triggered if userspace passes in too large timeout
value, larger than INT_MAX / HZ seconds. The kernel detects it and complains
about "schedule_timeout: wrong timeout value %lx" and generates a warning
backtrace.

Note that this fixes commit 6cedb8b3 ("drm/msm: avoid using 'timespec'"),
because the previously used timespec_to_jiffies() function returned unsigned
long instead of s64:
static inline unsigned long timespec_to_jiffies(const struct timespec *value)

Fixes: 6cedb8b3 ("drm/msm: avoid using 'timespec'")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jordan Crouse <jcrouse@codeaurora.org>
Cc: Rob Clark <robdclark@chromium.org>
Cc: stable@vger.kernel.org # 5.6+
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210917005913.157379-1-marex@denx.deSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_drv.h

@@ -504,7 +504,7 @@ static inline int align_pitch(int width, int bpp)
 static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
 {
 	ktime_t now = ktime_get();
-	unsigned long remaining_jiffies;
+	s64 remaining_jiffies;
 
 	if (ktime_compare(*timeout, now) < 0) {
 		remaining_jiffies = 0;
@@ -513,7 +513,7 @@ static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
 		remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
 	}
 
-	return remaining_jiffies;
+	return clamp(remaining_jiffies, 0LL, (s64)INT_MAX);
 }
 
 #endif /* __MSM_DRV_H__ */