linux-kernel - RE: [PATCH net-next] net: ethernet: renesas: Fix return type of rswitch_start

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Date:   Fri, 4 Nov 2022 04:29:42 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
CC:     Sergey Shtylyov <s.shtylyov@....ru>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH net-next] net: ethernet: renesas: Fix return type of
 rswitch_start_xmit()

Hi, Nathan,

> From: Nathan Chancellor, Sent: Friday, November 4, 2022 7:01 AM
> 
> 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
> proposed warning in clang aims to catch these at compile time, which
> reveals:
> 
>   drivers/net/ethernet/renesas/rswitch.c:1533:20: 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 = rswitch_start_xmit,
>                           ^~~~~~~~~~~~~~~~~~
>   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 rswitch_start_xmit()
> to match the prototype's to resolve the warning and CFI failure.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---

Thank you for the patch!

Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>

Best regards,
Yoshihiro Shimoda

>  drivers/net/ethernet/renesas/rswitch.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
> index 20df2020d3e5..f0168fedfef9 100644
> --- a/drivers/net/ethernet/renesas/rswitch.c
> +++ b/drivers/net/ethernet/renesas/rswitch.c
> @@ -1390,7 +1390,7 @@ static int rswitch_stop(struct net_device *ndev)
>  	return 0;
>  };
> 
> -static int rswitch_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> +static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  {
>  	struct rswitch_device *rdev = netdev_priv(ndev);
>  	struct rswitch_gwca_queue *gq = rdev->tx_queue;
> 
> base-commit: ef2dd61af7366e5a42e828fff04932e32eb0eacc
> --
> 2.38.1