On Thu, Jun 13, 2019 at 12:14:50PM -0700, Andy Lutomirski wrote: > 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? I think it would be a friendly way to help anyone wondering why something suddenly started segfaulting, yeah. Just a pr_warn_once() or something (not a WARN() since it's "intentionally" reachable by userspace). -- Kees Cook
