netdev - Re: [PATCH net] sfc: fix ef100 design-param checking

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Date:   Wed, 12 Aug 2020 08:23:05 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Edward Cree <ecree@...arflare.com>
Cc:     linux-net-drivers@...arflare.com, davem@...emloft.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH net] sfc: fix ef100 design-param checking

On Wed, Aug 12, 2020 at 10:32:49AM +0100, Edward Cree wrote:
> The handling of the RXQ/TXQ size granularity design-params had two
>  problems: it had a 64-bit divide that didn't build on 32-bit platforms,
>  and it could divide by zero if the NIC supplied 0 as the value of the
>  design-param.  Fix both by checking for 0 and for a granularity bigger
>  than our min-size; if the granularity <= EFX_MIN_DMAQ_SIZE then it fits
>  in 32 bits, so we can cast it to u32 for the divide.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Edward Cree <ecree@...arflare.com>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
> I've only build-tested this, and then only on 64-bit, since our lab's
>  cooling system can't cope with the heatwave and we keep having to shut
>  everything down :(
> 
>  drivers/net/ethernet/sfc/ef100_nic.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/sfc/ef100_nic.c b/drivers/net/ethernet/sfc/ef100_nic.c
> index 36598d0542ed..206d70f9d95b 100644
> --- a/drivers/net/ethernet/sfc/ef100_nic.c
> +++ b/drivers/net/ethernet/sfc/ef100_nic.c
> @@ -979,7 +979,8 @@ static int ef100_process_design_param(struct efx_nic *efx,
>  		 * EFX_MIN_DMAQ_SIZE is divisible by GRANULARITY.
>  		 * This is very unlikely to fail.
>  		 */
> -		if (EFX_MIN_DMAQ_SIZE % reader->value) {
> +		if (!reader->value || reader->value > EFX_MIN_DMAQ_SIZE ||
> +		    EFX_MIN_DMAQ_SIZE % (u32)reader->value) {
>  			netif_err(efx, probe, efx->net_dev,
>  				  "%s size granularity is %llu, can't guarantee safety\n",
>  				  reader->type == ESE_EF100_DP_GZ_RXQ_SIZE_GRANULARITY ? "RXQ" : "TXQ",