[PATCH v2 1/3] s390/ctcm: Fix return type of ctc{mp,}m_tx()

[PATCH v2 1/3] s390/ctcm: Fix return type of ctc{mp,}m_tx()

[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/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>
---
v2:
  - Pick up tags from Alexandra and Kees.
  - Remove comment block above ctcm_tx() (Alexandra).
v1: https://lore.kernel.org/20221102163252.49175-1-nathan@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 37b551bd43bf..bdfab9ea0046 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;

base-commit: 9abf2313adc1ca1b6180c508c25f22f9395cc780
-- 
2.38.1

[PATCH v2 2/3] s390/netiucv: Fix return type of netiucv_tx()

[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/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.

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>
---
v2:
  - Pick up tags from Alexandra and Kees.
  - Remove comment block above netiucv_tx() (Alexandra).
v1: https://lore.kernel.org/20221102163252.49175-2-nathan@kernel.org/
---
 drivers/s390/net/netiucv.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/drivers/s390/net/netiucv.c b/drivers/s390/net/netiucv.c
index 65aa0a96c21d..66076cada8ae 100644
--- a/drivers/s390/net/netiucv.c
+++ b/drivers/s390/net/netiucv.c
@@ -1248,15 +1248,8 @@ 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)
+static netdev_tx_t netiucv_tx(struct sk_buff *skb, struct net_device *dev)
 {
 	struct netiucv_priv *privptr = netdev_priv(dev);
 	int rc;
-- 
2.38.1

[PATCH v2 3/3] s390/lcs: Fix return type of lcs_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/s390/net/lcs.c:2090:21: 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         = lcs_start_xmit,
                                    ^~~~~~~~~~~~~~
  drivers/s390/net/lcs.c:2097:21: 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         = lcs_start_xmit,
                                    ^~~~~~~~~~~~~~

->ndo_start_xmit() in 'struct net_device_ops' expects a return type of
'netdev_tx_t', not 'int'. Adjust the return type of lcs_start_xmit() 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
Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
v2:
  - Pick up tags from Alexandra and Kees.
  - Adjust indentation of modified lines, as they can fit within the
    line limit (Alexandra).
v1: https://lore.kernel.org/20221102163252.49175-3-nathan@kernel.org/
---
 drivers/s390/net/lcs.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/s390/net/lcs.c b/drivers/s390/net/lcs.c
index 84c8981317b4..38f312664ce7 100644
--- a/drivers/s390/net/lcs.c
+++ b/drivers/s390/net/lcs.c
@@ -1519,9 +1519,8 @@ lcs_txbuffer_cb(struct lcs_channel *channel, struct lcs_buffer *buffer)
 /*
  * Packet transmit function called by network stack
  */
-static int
-__lcs_start_xmit(struct lcs_card *card, struct sk_buff *skb,
-		 struct net_device *dev)
+static netdev_tx_t __lcs_start_xmit(struct lcs_card *card, struct sk_buff *skb,
+				    struct net_device *dev)
 {
 	struct lcs_header *header;
 	int rc = NETDEV_TX_OK;
@@ -1582,8 +1581,7 @@ __lcs_start_xmit(struct lcs_card *card, struct sk_buff *skb,
 	return rc;
 }
 
-static int
-lcs_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t lcs_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct lcs_card *card;
 	int rc;
-- 
2.38.1

Re: [PATCH v2 1/3] s390/ctcm: Fix return type of ctc{mp,}m_tx()

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (master)
by David S. Miller <davem@davemloft.net>:

On Thu,  3 Nov 2022 10:01:28 -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:
  - [v2,1/3] s390/ctcm: Fix return type of ctc{mp,}m_tx()
    https://git.kernel.org/netdev/net-next/c/aa5bf80c3c06
  - [v2,2/3] s390/netiucv: Fix return type of netiucv_tx()
    https://git.kernel.org/netdev/net-next/c/88d86d18d7cf
  - [v2,3/3] s390/lcs: Fix return type of lcs_start_xmit()
    https://git.kernel.org/netdev/net-next/c/bb16db839365

You are awesome, thank you!
-- 
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