On Mon, Feb 05, 2018 at 04:37:26PM +0000, Andy Lutomirski wrote: > On Mon, Feb 5, 2018 at 4:30 PM, Ingo Molnar <[email protected]> wrote: > > > > * Andy Lutomirski <[email protected]> wrote: > > > >> > >> > >> > On Feb 5, 2018, at 3:42 AM, Ingo Molnar <[email protected]> wrote: > >> > > >> > > >> > * Dan Williams <[email protected]> wrote: > >> > > >> >> + /* > >> >> + * Sanitize extra registers of values that a speculation attack > >> >> + * might want to exploit. In the CONFIG_FRAME_POINTER=y case, > >> >> + * the expectation is that %ebp will be clobbered before it > >> >> + * could be used. > >> >> + */ > >> >> + .macro CLEAR_EXTRA_REGS_NOSPEC > >> >> + xorq %r15, %r15 > >> >> + xorq %r14, %r14 > >> >> + xorq %r13, %r13 > >> >> + xorq %r12, %r12 > >> >> + xorl %ebx, %ebx > >> >> +#ifndef CONFIG_FRAME_POINTER > >> >> + xorl %ebp, %ebp > >> >> +#endif > >> >> + .endm > >> > > >> > Yeah, so this series look pretty good to me, but there's one small > >> > detail: I think > >> > RBP should be cleared unconditionally here, even in the > >> > CONFIG_FRAME_POINTERS=y > >> > case, because: > >> > >> ENCODE_FRAME_POINTER should take care of rbp, though. > > > > AFAICS there's various entry paths where it's not used I think: for example > > the > > compat system calls in entry_64_compat.S don't seem to encode RBP in such a > > fashion (unless I missed some macro side effect). > > Then that's a separate bug that should be fixed. Josh?
We don't encode the frame pointer on syscalls, because "fast path" (though that's obviously no longer a consideration). -- Josh
