2019-12-15 11:41:15

by Remi Pommarel

Subject: [PATCH v2] clk: meson: pll: Fix by 0 division in __pll_params_to_rate()

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: 7a29a869434e ("clk: meson: Add support for Meson clock controller")
Signed-off-by: Remi Pommarel <[email protected]>
---
Changes since v1:
- Change Fix tag
- Move null test to .recalc_rate()
---
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..4d3a8003ca20 100644
--- a/drivers/clk/meson/clk-pll.c
+++ b/drivers/clk/meson/clk-pll.c
@@ -77,6 +77,10 @@ static unsigned long meson_clk_pll_recalc_rate(struct clk_hw *hw,
unsigned int m, n, frac;

n = meson_parm_read(clk->map, &pll->n);
+ /* Some hw may have n set to 0 at init, avoid div by 0 in that case */
+ if (n == 0)
+ return 0;
+
m = meson_parm_read(clk->map, &pll->m);

frac = MESON_PARM_APPLICABLE(&pll->frac) ?
--
2.24.0

2019-12-15 20:36:06

by Martin Blumenstingl

Subject: Re: [PATCH v2] clk: meson: pll: Fix by 0 division in __pll_params_to_rate()

On Sun, Dec 15, 2019 at 12:39 PM Remi Pommarel <[email protected]> wrote:
>
> 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: 7a29a869434e ("clk: meson: Add support for Meson clock controller")
> Signed-off-by: Remi Pommarel <[email protected]>
Reviewed-by: Martin Blumenstingl <[email protected]>

thank you for the patch Remi!


Martin