linux-kernel - Re: [PATCH] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup

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Message-id: <575A17F5.1050609@samsung.com>
Date:	Fri, 10 Jun 2016 10:29:25 +0900
From:	Seung-Woo Kim <sw0312.kim@...sung.com>
To:	Jaehoon Chung <jh80.chung@...sung.com>
Cc:	ulf.hansson@...aro.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Seung-Woo Kim <sw0312.kim@...sung.com>
Subject: Re: [PATCH] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

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.

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;
>>
> 
> 
> 

-- 
Seung-Woo Kim
Samsung Software R&D Center
--