Date:	Fri, 17 Jun 2016 10:30:50 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	sw0312.kim@...sung.com
Cc:	ulf.hansson@...aro.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

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@...sung.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;
>>>
>>
>>
>>
> 

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