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

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Message-Id: <20230319-pasemi-incompatible-pointer-types-strict-v1-1-1b9459d8aef0@kernel.org>
Date:   Sun, 19 Mar 2023 16:41:08 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Cc:     ndesaulniers@...gle.com, trix@...hat.com, netdev@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH net-next] net: pasemi: Fix return type of
 pasemi_mac_start_tx()

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.

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>