netdev - Re: [PATCH net-next] net: pasemi: Fix return type of pasemi_mac_start

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Date:   Mon, 20 Mar 2023 09:09:06 +0100
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Nathan Chancellor <nathan@...nel.org>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <ndesaulniers@...gle.com>, <trix@...hat.com>,
        <netdev@...r.kernel.org>, <llvm@...ts.linux.dev>,
        <patches@...ts.linux.dev>
Subject: Re: [PATCH net-next] net: pasemi: Fix return type of
 pasemi_mac_start_tx()

The 03/19/2023 16:41, Nathan Chancellor wrote:
> 
> With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
> indirect call targets are validated against the expected function
> pointer prototype to make sure the call target is valid to help mitigate
> ROP attacks. If they are not identical, there is a failure at run time,
> which manifests as either a kernel panic or thread getting killed. A
> warning in clang aims to catch these at compile time, which reveals:
> 
>   drivers/net/ethernet/pasemi/pasemi_mac.c:1665:21: error: incompatible function pointer types initializing 'netdev_tx_t (*)(struct sk_buff *, struct net_device *)' (aka 'enum netdev_tx (*)(struct sk_buff *, struct net_device *)') with an expression of type 'int (struct sk_buff *, struct net_device *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>           .ndo_start_xmit         = pasemi_mac_start_tx,
>                                     ^~~~~~~~~~~~~~~~~~~
>   1 error generated.
> 
> ->ndo_start_xmit() in 'struct net_device_ops' expects a return type of
> 'netdev_tx_t', not 'int'. Adjust the return type of
> pasemi_mac_start_tx() to match the prototype's to resolve the warning.
> While PowerPC does not currently implement support for kCFI, it could in
> the future, which means this warning becomes a fatal CFI failure at run
> time.

Reviewed-by: Horatiu Vultur <horatiu.vultur@...rochip.com>

> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  drivers/net/ethernet/pasemi/pasemi_mac.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/pasemi/pasemi_mac.c b/drivers/net/ethernet/pasemi/pasemi_mac.c
> index aaab590ef548..ed7dd0a04235 100644
> --- a/drivers/net/ethernet/pasemi/pasemi_mac.c
> +++ b/drivers/net/ethernet/pasemi/pasemi_mac.c
> @@ -1423,7 +1423,7 @@ static void pasemi_mac_queue_csdesc(const struct sk_buff *skb,
>         write_dma_reg(PAS_DMA_TXCHAN_INCR(txring->chan.chno), 2);
>  }
> 
> -static int pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
> +static netdev_tx_t pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
>  {
>         struct pasemi_mac * const mac = netdev_priv(dev);
>         struct pasemi_mac_txring * const txring = tx_ring(mac);
> 
> ---
> base-commit: e8d018dd0257f744ca50a729e3d042cf2ec9da65
> change-id: 20230319-pasemi-incompatible-pointer-types-strict-8569226f4e10
> 
> Best regards,
> --
> Nathan Chancellor <nathan@...nel.org>
> 

-- 
/Horatiu