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

[Kees Cook]

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