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List:       linux-hardening
Subject:    Re: [PATCH v2] Drivers: hv: vmbus: Split memcpy of flex-array
From:       Wei Liu <wei.liu () kernel ! org>
Date:       2022-09-28 13:36:06
Message-ID: YzRNxs6bVtNZdtNH () liuwe-devbox-debian-v2
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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@microsoft.com>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: Stephen Hemminger <sthemmin@microsoft.com>
> Cc: Wei Liu <wei.liu@kernel.org>
> Cc: Dexuan Cui <decui@microsoft.com>
> Cc: linux-hyperv@vger.kernel.org
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Reported-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Applied to hyperv-next. Thanks.


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