RE: [PATCH] wilc1000: fix DMA on stack objects

[David Laight <David.Laight@ACULAB.COM>]

From: Michael Walle
> Sent: 28 July 2022 16:21
> 
> From: Michael Walle <mwalle@kernel.org>
> 
> Sometimes wilc_sdio_cmd53() is called with addresses pointing to an
> object on the stack. E.g. wilc_sdio_write_reg() will call it with an
> address pointing to one of its arguments. Detect whether the buffer
> address is not DMA-able in which case a bounce buffer is used. The bounce
> buffer itself is protected from parallel accesses by sdio_claim_host().
> 
> Fixes: 5625f965d764 ("wilc1000: move wilc driver out of staging")
> Signed-off-by: Michael Walle <mwalle@kernel.org>
> ---
> The bug itself probably goes back way more, but I don't know if it makes
> any sense to use an older commit for the Fixes tag. If so, please suggest
> one.
> 
> The bug leads to an actual error on an imx8mn SoC with 1GiB of RAM. But the
> error will also be catched by CONFIG_DEBUG_VIRTUAL:
> [    9.817512] virt_to_phys used for non-linear address: (____ptrval____) (0xffff80000a94bc9c)
> 
>  .../net/wireless/microchip/wilc1000/sdio.c    | 28 ++++++++++++++++---
>  1 file changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/wireless/microchip/wilc1000/sdio.c
> b/drivers/net/wireless/microchip/wilc1000/sdio.c
> index 7962c11cfe84..e988bede880c 100644
> --- a/drivers/net/wireless/microchip/wilc1000/sdio.c
> +++ b/drivers/net/wireless/microchip/wilc1000/sdio.c
> @@ -27,6 +27,7 @@ struct wilc_sdio {
>  	bool irq_gpio;
>  	u32 block_size;
>  	int has_thrpt_enh3;
> +	u8 *dma_buffer;
>  };
> 
>  struct sdio_cmd52 {
> @@ -89,6 +90,9 @@ static int wilc_sdio_cmd52(struct wilc *wilc, struct sdio_cmd52 *cmd)
>  static int wilc_sdio_cmd53(struct wilc *wilc, struct sdio_cmd53 *cmd)
>  {
>  	struct sdio_func *func = container_of(wilc->dev, struct sdio_func, dev);
> +	struct wilc_sdio *sdio_priv = wilc->bus_data;
> +	bool need_bounce_buf = false;
> +	u8 *buf = cmd->buffer;
>  	int size, ret;
> 
>  	sdio_claim_host(func);
> @@ -100,12 +104,20 @@ static int wilc_sdio_cmd53(struct wilc *wilc, struct sdio_cmd53 *cmd)
>  	else
>  		size = cmd->count;
> 
> +	if ((!virt_addr_valid(buf) || object_is_on_stack(buf)) &&

How cheap are the above tests?
It might just be worth always doing the 'bounce'?

> +	    !WARN_ON_ONCE(size > WILC_SDIO_BLOCK_SIZE)) {

That WARN() ought to be an error return?
Or just assume that large buffers will dma-capable?

	David

> +		need_bounce_buf = true;
> +		buf = sdio_priv->dma_buffer;
> +	}
> +
>  	if (cmd->read_write) {  /* write */
> -		ret = sdio_memcpy_toio(func, cmd->address,
> -				       (void *)cmd->buffer, size);
> +		if (need_bounce_buf)
> +			memcpy(buf, cmd->buffer, size);
> +		ret = sdio_memcpy_toio(func, cmd->address, buf, size);
>  	} else {        /* read */
> -		ret = sdio_memcpy_fromio(func, (void *)cmd->buffer,
> -					 cmd->address,  size);
> +		ret = sdio_memcpy_fromio(func, buf, cmd->address, size);
> +		if (need_bounce_buf)
> +			memcpy(cmd->buffer, buf, size);
>  	}
> 
>  	sdio_release_host(func);
> @@ -127,6 +139,12 @@ static int wilc_sdio_probe(struct sdio_func *func,
>  	if (!sdio_priv)
>  		return -ENOMEM;
> 
> +	sdio_priv->dma_buffer = kzalloc(WILC_SDIO_BLOCK_SIZE, GFP_KERNEL);
> +	if (!sdio_priv->dma_buffer) {
> +		ret = -ENOMEM;
> +		goto free;
> +	}
> +
>  	ret = wilc_cfg80211_init(&wilc, &func->dev, WILC_HIF_SDIO,
>  				 &wilc_hif_sdio);
>  	if (ret)
> @@ -160,6 +178,7 @@ static int wilc_sdio_probe(struct sdio_func *func,
>  	irq_dispose_mapping(wilc->dev_irq_num);
>  	wilc_netdev_cleanup(wilc);
>  free:
> +	kfree(sdio_priv->dma_buffer);
>  	kfree(sdio_priv);
>  	return ret;
>  }
> @@ -171,6 +190,7 @@ static void wilc_sdio_remove(struct sdio_func *func)
> 
>  	clk_disable_unprepare(wilc->rtc_clk);
>  	wilc_netdev_cleanup(wilc);
> +	kfree(sdio_priv->dma_buffer);
>  	kfree(sdio_priv);
>  }
> 
> --
> 2.30.2

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