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Message-ID: <YzNqiLag6NyRMdh+@work> Date: Tue, 27 Sep 2022 16:26:32 -0500 From: "Gustavo A. R. Silva" <gustavoars@...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>, 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> Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org> Thanks! -- Gustavo > --- > v2: - fix commit log, add tags and exact warning test from Nathan > v1: https://lore.kernel.org/lkml/20220924030741.3345349-1-keescook@chromium.org > --- > drivers/hv/vmbus_drv.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c > index 23c680d1a0f5..9b111a8262e3 100644 > --- a/drivers/hv/vmbus_drv.c > +++ b/drivers/hv/vmbus_drv.c > @@ -1131,7 +1131,8 @@ void vmbus_on_msg_dpc(unsigned long data) > return; > > INIT_WORK(&ctx->work, vmbus_onmessage_work); > - memcpy(&ctx->msg, &msg_copy, sizeof(msg->header) + payload_size); > + ctx->msg.header = msg_copy.header; > + memcpy(&ctx->msg.payload, msg_copy.u.payload, payload_size); > > /* > * The host can generate a rescind message while we > -- > 2.34.1 >
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