[PATCH] clk: meson: pll: Fix by 0 division in __pll_params_to_rate()

Remi Pommarel
2019-12-08T21:14:07Z

Some meson pll registers can be initialized with 0 as N value, introducing
the following division by 0 when computing rate :

UBSAN: Undefined behaviour in drivers/clk/meson/clk-pll.c:75:9
division by zero
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc3-608075-g86c9af8630e1-dirty #400
Call trace:
dump_backtrace+0x0/0x1c0
show_stack+0x14/0x20
dump_stack+0xc4/0x100
ubsan_epilogue+0x14/0x68
__ubsan_handle_divrem_overflow+0x98/0xb8
__pll_params_to_rate+0xdc/0x140
meson_clk_pll_recalc_rate+0x278/0x3a0
__clk_register+0x7c8/0xbb0
devm_clk_hw_register+0x54/0xc0
meson_eeclkc_probe+0xf4/0x1a0
platform_drv_probe+0x54/0xd8
really_probe+0x16c/0x438
driver_probe_device+0xb0/0xf0
device_driver_attach+0x94/0xa0
__driver_attach+0x70/0x108
bus_for_each_dev+0xd8/0x128
driver_attach+0x30/0x40
bus_add_driver+0x1b0/0x2d8
driver_register+0xbc/0x1d0
__platform_driver_register+0x78/0x88
axg_driver_init+0x18/0x20
do_one_initcall+0xc8/0x24c
kernel_init_freeable+0x2b0/0x344
kernel_init+0x10/0x128
ret_from_fork+0x10/0x18

This checks if N is null before doing the division.

Fixes: 8289aafa4f36 ("clk: meson: improve pll driver results with frac")
Signed-off-by: Remi Pommarel <repk@triplefau.lt>
---
drivers/clk/meson/clk-pll.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
index ddb1e5634739..6649659f216a 100644
--- a/drivers/clk/meson/clk-pll.c
+++ b/drivers/clk/meson/clk-pll.c
@@ -66,6 +66,10 @@ static unsigned long __pll_params_to_rate(unsigned long parent_rate,
(1 << pll->frac.width));
}

+ /* Avoid by zero division */
+ if (n == 0)
+ return 0;
+
return DIV_ROUND_UP_ULL(rate, n);
}

--
2.24.0