On Fri, 12 Jan 2018, David Woodhouse wrote: > In accordance with the Intel and AMD documentation, we need to overwrite > all entries in the RSB on exiting a guest, to prevent malicious branch > target predictions from affecting the host kernel. This is needed both > for retpoline and for IBRS. > > [ak: numbers again for the RSB stuffing labels] > Signed-off-by: David Woodhouse <d...@amazon.co.uk> > Tested-by: Peter Zijlstra (Intel) <pet...@infradead.org> > --- > I love the smell of bikeshed paint in the morning. But to be fair, this > one was actually an issue which might possibly have bitten in the future. > > Can we please stop arguing about asm labels now though? Let's get this > stuff done, and we can set about the oh-so-important task of persuading > Linus to eliminate all numeric labels and rely on human-readable labels > with %= and \@ to make them unique, some time after the dust settles.
Fair enough. I surely like the below way more than the sloppy hackery from Andi which completely removed any form of documentation. > +#define __FILL_RETURN_BUFFER(reg, nr, sp) \ > + mov $(nr/2), reg; \ > +771: \ > + call 772f; \ > +773: /* speculation trap */ \ > + pause; \ > + jmp 773b; \ > +772: \ > + call 774f; \ > +775: /* speculation trap */ \ > + pause; \ > + jmp 775b; \ > +774: \ > + dec reg; \ > + jnz 771b; \ > + add $(BITS_PER_LONG/8) * nr, sp; > +
