Re: [PATCH v2] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

Jaehoon Chung
2016-06-20T03:06:47Z

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@samsung.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
>