[PATCH net-next] net: ethernet: renesas: Fix return type of rswitch_start_xmit()

[PATCH net-next] net: ethernet: renesas: Fix return type of rswitch_start_xmit()

[Nathan Chancellor]

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@kernel.org>
---
 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

RE: [PATCH net-next] net: ethernet: renesas: Fix return type of rswitch_start_xmit()

[Yoshihiro Shimoda]

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@kernel.org>
> ---

Thank you for the patch!

Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.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

Re: [PATCH net-next] net: ethernet: renesas: Fix return type of rswitch_start_xmit()

[Kees Cook]

On Thu, Nov 03, 2022 at 03:00:32PM -0700, 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/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@kernel.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH net-next] net: ethernet: renesas: Fix return type of rswitch_start_xmit()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  3 Nov 2022 15:00:32 -0700 you 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:
> 
> [...]

Here is the summary with links:
  - [net-next] net: ethernet: renesas: Fix return type of rswitch_start_xmit()
    https://git.kernel.org/netdev/net-next/c/8e0aa1ff44ca

You are awesome, thank you!
-- 
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