linux-kernel - Re: [PATCH] HSI: ssi_protocol: Fix return type of ssip_pn

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Date:   Mon, 14 Nov 2022 21:51:48 +0100
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Sami Tolvanen <samitolvanen@...gle.com>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] HSI: ssi_protocol: Fix return type of ssip_pn_xmit()

Hi,

On Wed, Nov 02, 2022 at 12:07:02PM -0700, Kees Cook wrote:
> On Wed, Nov 02, 2022 at 09:02:33AM -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/hsi/clients/ssi_protocol.c:1053:20: 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 = ssip_pn_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 ssip_pn_xmit() to
> > match the prototype's to resolve the warning and CFI failure.
> > Additionally, use the enum 'NETDEV_TX_OK' instead of a raw '0' for the
> > return value of ssip_pn_xmit().
> > 
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> > Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>

Thanks, queued.

-- Sebastian

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