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Message-ID: <202209232119.E32C14857@keescook> Date: Fri, 23 Sep 2022 21:22:55 -0700 From: Kees Cook <keescook@...omium.org> To: "K. Y. Srinivasan" <kys@...rosoft.com> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, 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>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] Drivers: hv: vmbus: Split memcpy of flex-array 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
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