From: Kees Cook <keescook@chromium.org>
To: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
linux-hyperv@vger.kernel.org,
Nathan Chancellor <nathan@kernel.org>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] Drivers: hv: vmbus: Split memcpy of flex-array
Date: Fri, 23 Sep 2022 21:22:55 -0700 [thread overview]
Message-ID: <202209232119.E32C14857@keescook> (raw)
In-Reply-To: <Yy58rt9N0+dHrNtt@work>
On Fri, Sep 23, 2022 at 10:42:38PM -0500, Gustavo A. R. Silva wrote:
> On Fri, Sep 23, 2022 at 08:07:41PM -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. As it
> > turns out, this appears to actually reduce the text size:
Er, actually, I can't read/math. ;) It _does_ grow the text size. (That's
2_3_ not 22 at the start of the text size...) On examination, it appears
to unroll the already inlined memcpy further.
> >
> > $ 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
^
-Kees
--
Kees Cook
next prev parent reply other threads:[~2022-09-24 4:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-24 3:07 [PATCH] Drivers: hv: vmbus: Split memcpy of flex-array Kees Cook
2022-09-24 3:42 ` Gustavo A. R. Silva
2022-09-24 4:22 ` Kees Cook [this message]
2022-09-24 10:34 ` Wei Liu
2022-09-27 21:23 ` Kees Cook
2022-09-27 20:46 ` Nathan Chancellor
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