Re: [PATCH net] net: ipa: compute DMA pool size properly

[Bjorn Andersson]

On Sun, Mar 26, 2023 at 11:52:23AM -0500, Alex Elder wrote:
> In gsi_trans_pool_init_dma(), the total size of a pool of memory
> used for DMA transactions is calculated.  However the calculation is
> done incorrectly.
> 
> For 4KB pages, this total size is currently always more than one
> page, and as a result, the calculation produces a positive (though
> incorrect) total size.  The code still works in this case; we just
> end up with fewer DMA pool entries than we intended.
> 
> Bjorn Andersson tested booting a kernel with 16KB pages, and hit a
> null pointer derereference in sg_alloc_append_table_from_pages(),
> descending from gsi_trans_pool_init_dma().  The cause of this was
> that a 16KB total size was going to be allocated, and with 16KB
> pages the order of that allocation is 0.  The total_size calculation
> yielded 0, which eventually led to the crash.
> 
> Correcting the total_size calculation fixes the problem.
> 
> Reported-by: <quic_bjorande@xxxxxxxxxxx>
> Tested-by: <quic_bjorande@xxxxxxxxxxx>

It would be nice to add "Bjorn Andersson" to these two.

Regards,
Bjorn

> Fixes: 9dd441e4ed57 ("soc: qcom: ipa: GSI transactions")
> Signed-off-by: Alex Elder <elder@xxxxxxxxxx>
> ---
>  drivers/net/ipa/gsi_trans.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ipa/gsi_trans.c b/drivers/net/ipa/gsi_trans.c
> index 0f52c068c46d6..ee6fb00b71eb6 100644
> --- a/drivers/net/ipa/gsi_trans.c
> +++ b/drivers/net/ipa/gsi_trans.c
> @@ -156,7 +156,7 @@ int gsi_trans_pool_init_dma(struct device *dev, struct gsi_trans_pool *pool,
>  	 * gsi_trans_pool_exit_dma() can assume the total allocated
>  	 * size is exactly (count * size).
>  	 */
> -	total_size = get_order(total_size) << PAGE_SHIFT;
> +	total_size = PAGE_SIZE << get_order(total_size);
>  
>  	virt = dma_alloc_coherent(dev, total_size, &addr, GFP_KERNEL);
>  	if (!virt)
> -- 
> 2.34.1
>