netdev - Re: [PATCH v2] hv_netvsc: Fix netvsc_start

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Date:   Fri, 01 May 2020 15:25:12 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     natechancellor@...il.com
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, samitolvanen@...gle.com
Subject: Re: [PATCH v2] hv_netvsc: Fix netvsc_start_xmit's return type

From: Nathan Chancellor <natechancellor@...il.com>
Date: Tue, 28 Apr 2020 10:54:56 -0700

> netvsc_start_xmit is used as a callback function for the ndo_start_xmit
> function pointer. ndo_start_xmit's return type is netdev_tx_t but
> netvsc_start_xmit's return type is int.
> 
> This causes a failure with Control Flow Integrity (CFI), which requires
> function pointer prototypes and callback function definitions to match
> exactly. When CFI is in enforcing, the kernel panics. When booting a
> CFI kernel with WSL 2, the VM is immediately terminated because of this.
> 
> The splat when CONFIG_CFI_PERMISSIVE is used:
 ...
> Avoid this by using the right return type for netvsc_start_xmit.
> 
> Fixes: fceaf24a943d8 ("Staging: hv: add the Hyper-V virtual network driver")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1009
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

Applied.