Re: [PATCH 5/5] x86/vsyscall: Change the default vsyscall mode to xonly

[Andy Lutomirski]

On Mon, Jun 10, 2019 at 1:44 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Mon, Jun 10, 2019 at 01:25:31PM -0700, Andy Lutomirski wrote:
> > The use case for full emulation over xonly is very esoteric.  Let's
> > change the default to the safer xonly mode.
>
> Perhaps describe the esoteric cases here (and maybe in the Kconfig help
> text)? That should a user determine if they actually need it. (What
> would the failure under xonly look like for someone needing emulate?)

I added it to the Kconfig text.

Right now, the failure will just be a segfault.  I could add some
logic so that it would log "invalid read to vsyscall page -- fix your
userspace or boot with vsyscall=emulate".  Do you think that's
important?

--Andy