The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From e84cb605e02f1b3d0aee8d7157419cd8aaa06038 Mon Sep 17 00:00:00 2001
From: Boris Brezillon boris.brezillon@bootlin.com Date: Thu, 18 Oct 2018 12:02:50 +0200 Subject: [PATCH] drm/sun4i: Fix an ulong overflow in the dotclock driver
The calculated ideal rate can easily overflow an unsigned long, thus making the best div selection buggy as soon as no ideal match is found before the overflow occurs.
Fixes: 4731a72df273 ("drm/sun4i: request exact rates to our parents") Cc: stable@vger.kernel.org Signed-off-by: Boris Brezillon boris.brezillon@bootlin.com Acked-by: Maxime Ripard maxime.ripard@bootlin.com Signed-off-by: Maxime Ripard maxime.ripard@bootlin.com Link: https://patchwork.freedesktop.org/patch/msgid/20181018100250.12565-1-boris.b...
diff --git a/drivers/gpu/drm/sun4i/sun4i_dotclock.c b/drivers/gpu/drm/sun4i/sun4i_dotclock.c index e36004fbe453..2a15f2f9271e 100644 --- a/drivers/gpu/drm/sun4i/sun4i_dotclock.c +++ b/drivers/gpu/drm/sun4i/sun4i_dotclock.c @@ -81,9 +81,19 @@ static long sun4i_dclk_round_rate(struct clk_hw *hw, unsigned long rate, int i;
for (i = tcon->dclk_min_div; i <= tcon->dclk_max_div; i++) { - unsigned long ideal = rate * i; + u64 ideal = (u64)rate * i; unsigned long rounded;
+ /* + * ideal has overflowed the max value that can be stored in an + * unsigned long, and every clk operation we might do on a + * truncated u64 value will give us incorrect results. + * Let's just stop there since bigger dividers will result in + * the same overflow issue. + */ + if (ideal > ULONG_MAX) + goto out; + rounded = clk_hw_round_rate(clk_hw_get_parent(hw), ideal);