| Message ID | 20191208212206.16808-1-repk@triplefau.lt (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Neil Armstrong |
| Headers | show |
| Series | clk: meson: pll: Fix by 0 division in __pll_params_to_rate() | expand |
On Sun 08 Dec 2019 at 22:22, Remi Pommarel <repk@triplefau.lt> 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. Thanks for reporting this > > Fixes: 8289aafa4f36 ("clk: meson: improve pll driver results with > frac") In mainline, the commit above went in with sha1 3c4fe763d64d. Also, this commit is not really responsible for the problem. Having HW initialized with N = 0 would have failed since the beginning, I believe. In this case the correct fixes would be: Fixes: 7a29a869434e ("clk: meson: Add support for Meson clock controller") > 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; This can only really happen after init, in recalc() rate. I would much prefer if you could check the n value right after it is read (meson_parm_read()) in .recalc_rate() and add a comment explaining that some HW may have this parameter set 0 on init. > + > return DIV_ROUND_UP_ULL(rate, n); > }
On Mon, Dec 09, 2019 at 10:51:13AM +0100, Jerome Brunet wrote: > > On Sun 08 Dec 2019 at 22:22, Remi Pommarel <repk@triplefau.lt> 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. > > Thanks for reporting this > > > > > Fixes: 8289aafa4f36 ("clk: meson: improve pll driver results with > > frac") > > In mainline, the commit above went in with sha1 3c4fe763d64d. > > Also, this commit is not really responsible for the problem. Having HW > initialized with N = 0 would have failed since the beginning, I believe. > > In this case the correct fixes would be: > Fixes: 7a29a869434e ("clk: meson: Add support for Meson clock controller") > > > > 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; > > This can only really happen after init, in recalc() rate. > > I would much prefer if you could check the n value right after it is > read (meson_parm_read()) in .recalc_rate() and add a comment explaining > that some HW may have this parameter set 0 on init. > Sure will do. Thanks for reviewing this.
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); }
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(+)