linux-kernel - Re: [PATCH v2] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup

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Message-id: <57675635.20808@samsung.com>
Date:	Mon, 20 Jun 2016 11:34:29 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Seung-Woo Kim <sw0312.kim@...sung.com>, ulf.hansson@...aro.org,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

Hi SeungWoo,

On 06/17/2016 02:16 PM, Seung-Woo Kim wrote:
> This patch removes following UBSAN warnings in dw_mci_setup_bus().
> 
>   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 warnings are caused because of shift with more than 31 on 32
> bit variable, so this patch fixes to keep both clock and divider
> instead of shift.
> 
> Signed-off-by: Seung-Woo Kim <sw0312.kim@...sung.com>
> ---
>  drivers/mmc/host/dw_mmc.c |    8 +++++---
>  drivers/mmc/host/dw_mmc.h |    8 +++++---
>  2 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 2cc6123..d05c8cc 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 (clock != slot->__clk_old || div != slot->__div_old ||
> +		    force_clkinit)

I have realized why we put this condition..after checking your below codes.
This was patch to avoid the spamming for CONFIG_MMC_CLKGATE..
but CONFIG_MMC_CLKAGET didn't use anymore.. I think we can remove this condition.

How about?

Best Regards,
Jaehoon Chung

>  			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,
> @@ -1128,8 +1129,9 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>  		/* inform CIU */
>  		mci_send_cmd(slot, sdmmc_cmd_bits, 0);
>  
> -		/* keep the clock with reflecting clock dividor */
> -		slot->__clk_old = clock << div;
> +		/* keep the clock and clock divider */
> +		slot->__clk_old = clock;
> +		slot->__div_old = div;
>  	}
>  
>  	host->current_speed = clock;
> diff --git a/drivers/mmc/host/dw_mmc.h b/drivers/mmc/host/dw_mmc.h
> index 1e8d838..fdfc3f5 100644
> --- a/drivers/mmc/host/dw_mmc.h
> +++ b/drivers/mmc/host/dw_mmc.h
> @@ -245,9 +245,10 @@ extern int dw_mci_resume(struct dw_mci *host);
>   * @queue_node: List node for placing this node in the @queue list of
>   *	&struct dw_mci.
>   * @clock: Clock rate configured by set_ios(). Protected by host->lock.
> - * @__clk_old: The last updated clock with reflecting clock divider.
> - *	Keeping track of this helps us to avoid spamming the console
> - *	with CONFIG_MMC_CLKGATE.
> + * @__clk_old: The last updated clock.
> + * @__div_old: The last updated clock divider.
> + *	Keeping track of clock and clock divider helps us to avoid spamming
> + *	the console with CONFIG_MMC_CLKGATE.
>   * @flags: Random state bits associated with the slot.
>   * @id: Number of this slot.
>   * @sdio_id: Number of this slot in the SDIO interrupt registers.
> @@ -263,6 +264,7 @@ struct dw_mci_slot {
>  
>  	unsigned int		clock;
>  	unsigned int		__clk_old;
> +	unsigned int		__div_old;
>  
>  	unsigned long		flags;
>  #define DW_MMC_CARD_PRESENT	0
>