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From: Kees Cook <keescook@chromium.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: masahiroy@kernel.org, ndesaulniers@google.com, morbo@google.com,
	justinstitt@google.com, samitolvanen@google.com,
	nicolas@fjasle.eu, linux-kbuild@vger.kernel.org,
	llvm@lists.linux.dev, patches@lists.linux.dev,
	kernel test robot <lkp@intel.com>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	richard@nod.at, johannes@sipsolutions.net,
	linux-um@lists.infradead.org
Subject: Re: [PATCH v2 1/2] um: net: Fix return type of uml_net_start_xmit()
Date: Wed, 6 Dec 2023 12:30:40 -0800	[thread overview]
Message-ID: <202312061230.2210A1FE@keescook> (raw)
In-Reply-To: <20231206-enable-wincompatible-function-pointer-types-strict-w-1-v2-1-91311b4c37b0@kernel.org>

On Wed, Dec 06, 2023 at 09:49:46AM -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
> warning in clang aims to catch these at compile time, which reveals:
> 
>   arch/um/drivers/net_kern.c:353:21: warning: 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 *)' [-Wincompatible-function-pointer-types-strict]
>     353 |         .ndo_start_xmit         = uml_net_start_xmit,
>         |                                   ^~~~~~~~~~~~~~~~~~
>   1 warning generated.
> 
> ->ndo_start_xmit() in 'struct net_device_ops' expects a return type of
> 'netdev_tx_t', not 'int'. Adjust the return type of uml_net_start_xmit()
> to match the prototype's to resolve the warning. While UML does not
> currently implement support for kCFI, it could in the future, which
> means this warning becomes a fatal CFI failure at run time.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202310031340.v1vPh207-lkp@intel.com/
> Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Yes please. :)

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

-- 
Kees Cook

  reply	other threads:[~2023-12-06 20:30 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-12-06 16:49 [PATCH v2 0/2] Enable -Wincompatible-function-pointer-types-strict under W=1 Nathan Chancellor
2023-12-06 16:49 ` [PATCH v2 1/2] um: net: Fix return type of uml_net_start_xmit() Nathan Chancellor
2023-12-06 20:30   ` Kees Cook [this message]
2023-12-06 16:49 ` [PATCH v2 2/2] kbuild: Enable -Wincompatible-function-pointer-types-strict in W=1 Nathan Chancellor
2023-12-06 20:31   ` Kees Cook

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