Re: [PATCH 2/3] s390/netiucv: Fix return type of netiucv_tx()

Alexandra Winter
2022-11-03T12:10:18Z

On 02.11.22 17:32, 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
> proposed warning in clang aims to catch these at compile time, which
> reveals:
>
> drivers/s390/net/netiucv.c:1854:21: 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 = netiucv_tx,
> ^~~~~~~~~~
>
> ->ndo_start_xmit() in 'struct net_device_ops' expects a return type of
> 'netdev_tx_t', not 'int'. Adjust the return type of netiucv_tx() to
> match the prototype's to resolve the warning and potential CFI failure,
> should s390 select ARCH_SUPPORTS_CFI_CLANG in the future.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> drivers/s390/net/netiucv.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/s390/net/netiucv.c b/drivers/s390/net/netiucv.c
> index 65aa0a96c21d..1a7f2bc3a87b 100644
> --- a/drivers/s390/net/netiucv.c
> +++ b/drivers/s390/net/netiucv.c
> @@ -1256,7 +1256,7 @@ static int netiucv_close(struct net_device *dev)
> * Note: If we return !0, then the packet is free'd by
> * the generic network layer.
> */
> -static int netiucv_tx(struct sk_buff *skb, struct net_device *dev)
> +static netdev_tx_t netiucv_tx(struct sk_buff *skb, struct net_device *dev)
> {
> struct netiucv_priv *privptr = netdev_priv(dev);
> int rc;

Could you please also remove the corresponding comments:
diff --git a/drivers/s390/net/netiucv.c b/drivers/s390/net/netiucv.c
index 65aa0a96c21d..21e36f63fbc7 100644
--- a/drivers/s390/net/netiucv.c
+++ b/drivers/s390/net/netiucv.c
@@ -1248,13 +1248,6 @@ static int netiucv_close(struct net_device *dev)
/*
* Start transmission of a packet.
* Called from generic network device layer.
- *
- * @param skb Pointer to buffer containing the packet.
- * @param dev Pointer to interface struct.
- *
- * @return 0 if packet consumed, !0 if packet rejected.
- * Note: If we return !0, then the packet is free'd by
- * the generic network layer.
*/
static int netiucv_tx(struct sk_buff *skb, struct net_device *dev)
{

Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>