Subject: Re: [PATCH] ath10k: fix invalid dma_addr_t token assignment

From: Kalle Valo <[email-masked]>
Date: Mon, 18 Oct 2021 16:10:21 +0300

Arnd Bergmann <[email-masked]> writes:

> From: Arnd Bergmann <[email-masked]>
>
> Using a kernel pointer in place of a dma_addr_t token can
> lead to undefined behavior if that makes it into cache
> management functions. The compiler caught one such attempt
> in a cast:
>
> drivers/net/wireless/ath/ath10k/mac.c: In function 'ath10k_add_interface':
> drivers/net/wireless/ath/ath10k/mac.c:5586:47: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
>  5586 |                         arvif->beacon_paddr = (dma_addr_t)arvif->beacon_buf;
>       |                                               ^
>
> Looking through how this gets used down the way, I'm fairly
> sure that beacon_paddr is never accessed again for ATH10K_DEV_TYPE_HL
> devices, and if it was accessed, that would be a bug.

That's my understanding as well. beacon_paddr is only accessed in
ath10k_wmi_event_host_swba() and only low latency (ATH10K_DEV_TYPE_LL)
should use that function.

> Change the assignment to use a known-invalid address token
> instead, which avoids the warning and makes it easier to catch
> bugs if it does end up getting used.
>
> Fixes: e263bdab9c0e ("ath10k: high latency fixes for beacon buffer")
> Signed-off-by: Arnd Bergmann <[email-masked]>
> ---
>  drivers/net/wireless/ath/ath10k/mac.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
> index 7ca68c81d9b6..c0e78eaa65f8 100644
> --- a/drivers/net/wireless/ath/ath10k/mac.c
> +++ b/drivers/net/wireless/ath/ath10k/mac.c
> @@ -5583,7 +5583,7 @@ static int ath10k_add_interface(struct ieee80211_hw *hw,
>  		if (ar->bus_param.dev_type == ATH10K_DEV_TYPE_HL) {
>  			arvif->beacon_buf = kmalloc(IEEE80211_MAX_FRAME_LEN,
>  						    GFP_KERNEL);
> -			arvif->beacon_paddr = (dma_addr_t)arvif->beacon_buf;
> +			arvif->beacon_paddr = DMA_MAPPING_ERROR;

In the pending branch I added a comment here:

https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=02a383c9bf959147a95c4efeaa4edf35c4450fac

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