Re: [PATCH] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

Jaehoon Chung
2016-06-17T01:30:50Z

Hi Seung-Woo,

On 06/10/2016 10:29 AM, Seung-Woo Kim wrote:
> Hi Jaehoon,
>
> On 2016년 06월 09일 21:38, Jaehoon Chung wrote:
>> Hi Seung-Woo,
>>
>> On 06/08/2016 01:07 PM, Seung-Woo Kim wrote:
>>> This patch removes following UBSAN warnings in dw_mci_setup_bus().
>>> The warnings are caused because of shift with more than 31 on 32
>>> bit variable, so this patch fixes to shift only for less than 32.
>>>
>>> UBSAN: Undefined behaviour in drivers/mmc/host/dw_mmc.c:1102:14
>>> shift exponent 250 is too large for 32-bit type 'unsigned int'
>>> Call trace:
>>> [<ffffff90080908a8>] dump_backtrace+0x0/0x380
>>> [<ffffff9008090c3c>] show_stack+0x14/0x20
>>> [<ffffff90087457b8>] dump_stack+0xe0/0x120
>>> [<ffffff90087b1360>] ubsan_epilogue+0x18/0x68
>>> [<ffffff90087b1a94>] __ubsan_handle_shift_out_of_bounds+0x18c/0x1bc
>>> [<ffffff9008d89cb8>] dw_mci_setup_bus+0x3a0/0x438
>>> [...]
>>>
>>> UBSAN: Undefined behaviour in drivers/mmc/host/dw_mmc.c:1132:27
>>> shift exponent 250 is too large for 32-bit type 'unsigned int'
>>> Call trace:
>>> [<ffffff90080908a8>] dump_backtrace+0x0/0x380
>>> [<ffffff9008090c3c>] show_stack+0x14/0x20
>>> [<ffffff90087457b8>] dump_stack+0xe0/0x120
>>> [<ffffff90087b1360>] ubsan_epilogue+0x18/0x68
>>> [<ffffff90087b1a94>] __ubsan_handle_shift_out_of_bounds+0x18c/0x1bc
>>> [<ffffff9008d89c9c>] dw_mci_setup_bus+0x384/0x438
>>
>> The below message can be discarded.
>
> You are right, like above message, below part can be replaced as [...].
>
>>
>>> [<ffffff9008d89ed4>] dw_mci_set_ios+0x184/0x798
>>> [<ffffff9008d550ac>] mmc_power_up+0x11c/0x260
>>> [<ffffff9008d56b78>] mmc_start_host+0x88/0x100
>>> [<ffffff9008d583f4>] mmc_add_host+0x6c/0x128
>>> [<ffffff9008d88f90>] dw_mci_probe+0x1088/0x1750
>>> [<ffffff9008d8caa8>] dw_mci_pltfm_register+0x108/0x178
>>> [<ffffff9008d8dae4>] dw_mci_exynos_probe+0x4c/0x88
>>> [<ffffff9008a03838>] platform_drv_probe+0x78/0x180
>>> [<ffffff90089fe9fc>] driver_probe_device+0x144/0x460
>>> [<ffffff90089fee0c>] __driver_attach+0xf4/0x140
>>> [<ffffff90089fad98>] bus_for_each_dev+0xf0/0x160
>>> [<ffffff90089fdc9c>] driver_attach+0x34/0x58
>>> [<ffffff90089fd3e0>] bus_add_driver+0x2c0/0x398
>>> [<ffffff9008a00924>] driver_register+0xbc/0x1e0
>>> [<ffffff9008a02a94>] __platform_driver_register+0x84/0xa8
>>> [<ffffff9009dd5730>] dw_mci_exynos_pltfm_driver_init+0x18/0x20
>>> [<ffffff9008082df8>] do_one_initcall+0xa0/0x2c8
>>> [<ffffff9009d81780>] kernel_init_freeable+0x52c/0x5dc
>>> [<ffffff9009519844>] kernel_init+0x1c/0xf8
>>> [<ffffff9008086e10>] ret_from_fork+0x10/0x40
>>>
>>> Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
>>> ---
>>> drivers/mmc/host/dw_mmc.c | 5 +++--
>>> 1 files changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>> index 2cc6123..dff045e 100644
>>> --- a/drivers/mmc/host/dw_mmc.c
>>> +++ b/drivers/mmc/host/dw_mmc.c
>>> @@ -1099,7 +1099,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>>>
>>> div = (host->bus_hz != clock) ? DIV_ROUND_UP(div, 2) : 0;
>>>
>>> - if ((clock << div) != slot->__clk_old || force_clkinit)
>>> + if (((div < 32) ? (clock << div) : 0) != slot->__clk_old ||
>>
>> Well, we don't expect that clock is 0.
>> if clock is 0, it should be passed to " if (!clock)"..
>>
>> During initializing card, clock is 400KHz or less..I understood what you want to fix.
>> But I taught this is not correct.
>
> It seems slot->__clk_old is not really clock but a kind of value to
> store both clock and div in one variable. And at least, my compiler
> calculates right shift with more than 32 as 0. I am not sure there is
> other proper value for the case.
>
> By the way, in my test environment, clock is calculated as like
> following steps:
> mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 400000Hz,
> actual 400000HZ div = 250)
> mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz,
> actual 200000000HZ div = 0)
> mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 52000000Hz,
> actual 50000000HZ div = 2)
> mmc_host mmc0: Bus speed (slot 0) = 400000000Hz (slot req 52000000Hz,
> actual 50000000HZ div = 4)
> mmc_host mmc0: Bus speed (slot 0) = 400000000Hz (slot req 200000000Hz,
> actual 200000000HZ div = 1)
>
> and only the first case is reported as the warning. If you let me know
> any proper value, then I will fix with the value.

I think that "clock << div" and__old_clock are used for checking whether clock is changed.
So it doesn't need to rotate with div.

Could you check the below codes?

if ((clock != slot->clk_old) || force_clkinit)
...

slot->__clk_old = clock;

Best Regards,
Jaehoon Chung

>
> Thanks,
> - Seung-Woo Kim
>
>
>>
>>
>>> + force_clkinit)
>>> dev_info(&slot->mmc->class_dev,
>>> "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ div = %d)\n",
>>> slot->id, host->bus_hz, clock,
>>> @@ -1129,7 +1130,7 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>>> mci_send_cmd(slot, sdmmc_cmd_bits, 0);
>>>
>>> /* keep the clock with reflecting clock dividor */
>>> - slot->__clk_old = clock << div;
>>> + slot->__clk_old = (div < 32) ? (clock << div) : 0;
>>
>> Also, clock is not 0..
>>
>>
>> Best Regards,
>> Jaehoon Chung
>>
>>> }
>>>
>>> host->current_speed = clock;
>>>
>>
>>
>>
>