linux-hardening - Re: [PATCH v2] Drivers: hv: vmbus: Split memcpy of flex-array

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Message-ID: <YzRNxs6bVtNZdtNH@liuwe-devbox-debian-v2>
Date:   Wed, 28 Sep 2022 13:36:06 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        linux-hyperv@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] Drivers: hv: vmbus: Split memcpy of flex-array

On Tue, Sep 27, 2022 at 02:17:36PM -0700, Kees Cook wrote:
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), split the memcpy() of the header and the payload
> so no false positive run-time overflow warning will be generated. This
> results in the already inlined memcpy getting unrolled a little more,
> which very slightly increases text size:
> 
> $ size drivers/hv/vmbus_drv.o.before drivers/hv/vmbus_drv.o
>    text    data     bss     dec     hex filename
>   22968    5239     232   28439    6f17 drivers/hv/vmbus_drv.o.before
>   23032    5239     232   28503    6f57 drivers/hv/vmbus_drv.o
> 
> Avoids the run-time false-positive warning:
> 
>   memcpy: detected field-spanning write (size 212) of single field "&ctx->msg" at drivers/hv/vmbus_drv.c:1133 (size 16)
> 
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org/
> 
> Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: Wei Liu <wei.liu@...nel.org>
> Cc: Dexuan Cui <decui@...rosoft.com>
> Cc: linux-hyperv@...r.kernel.org
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Reported-by: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Tested-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Applied to hyperv-next. Thanks.