4.18-stable review patch. If anyone has any objections, please let me know.
------------------ From: Boris Brezillon <[email protected]> commit e84cb605e02f1b3d0aee8d7157419cd8aaa06038 upstream. 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: <[email protected]> Signed-off-by: Boris Brezillon <[email protected]> Acked-by: Maxime Ripard <[email protected]> Signed-off-by: Maxime Ripard <[email protected]> Link: https://patchwork.freedesktop.org/patch/msgid/[email protected] Signed-off-by: Greg Kroah-Hartman <[email protected]> --- drivers/gpu/drm/sun4i/sun4i_dotclock.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) --- 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 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);
