From: Nathan Chancellor nathan@kernel.org
[ Upstream commit aa5bf80c3c067b82b4362cd6e8e2194623bcaca6 ]
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/ctcm_main.c:1064:21: 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 = ctcm_tx, ^~~~~~~ drivers/s390/net/ctcm_main.c:1072:21: 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 = ctcmpc_tx, ^~~~~~~~~
->ndo_start_xmit() in 'struct net_device_ops' expects a return type of 'netdev_tx_t', not 'int'. Adjust the return type of ctc{mp,}m_tx() to match the prototype's to resolve the warning and potential CFI failure, should s390 select ARCH_SUPPORTS_CFI_CLANG in the future.
Additionally, while in the area, remove a comment block that is no longer relevant.
Link: https://github.com/ClangBuiltLinux/linux/issues/1750 Reviewed-by: Alexandra Winter wintera@linux.ibm.com Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Nathan Chancellor nathan@kernel.org Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/s390/net/ctcm_main.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-)
diff --git a/drivers/s390/net/ctcm_main.c b/drivers/s390/net/ctcm_main.c index fd705429708e..f91b6cfd7ed0 100644 --- a/drivers/s390/net/ctcm_main.c +++ b/drivers/s390/net/ctcm_main.c @@ -825,16 +825,9 @@ static int ctcmpc_transmit_skb(struct channel *ch, struct sk_buff *skb) /** * Start transmission of a packet. * Called from generic network device layer. - * - * skb Pointer to buffer containing the packet. - * dev Pointer to interface struct. - * - * returns 0 if packet consumed, !0 if packet rejected. - * Note: If we return !0, then the packet is free'd by - * the generic network layer. */ /* first merge version - leaving both functions separated */ -static int ctcm_tx(struct sk_buff *skb, struct net_device *dev) +static netdev_tx_t ctcm_tx(struct sk_buff *skb, struct net_device *dev) { struct ctcm_priv *priv = dev->ml_priv;
@@ -877,7 +870,7 @@ static int ctcm_tx(struct sk_buff *skb, struct net_device *dev) }
/* unmerged MPC variant of ctcm_tx */ -static int ctcmpc_tx(struct sk_buff *skb, struct net_device *dev) +static netdev_tx_t ctcmpc_tx(struct sk_buff *skb, struct net_device *dev) { int len = 0; struct ctcm_priv *priv = dev->ml_priv;