Messages in this thread | | | Subject | Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch | From | Andy Lutomirski <> | Date | Mon, 18 Feb 2019 18:20:07 -0800 |
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> On Feb 18, 2019, at 4:24 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> On Mon, Feb 18, 2019 at 2:31 PM H. Peter Anvin <hpa@zytor.com> wrote: >> >> The question is what "fix it" means. I'm really concerned about AC escapes, >> and everyone else should be, too. > > I do think that it might be the right thing to do to add some kind of > WARN_ON_ONCE() for AC being set in various can-reschedule situations. > > We'd just have to abstract it sanely. I'm sure arm64 has the exact > same issue with PAN - maybe it saves properly, but the same "we > wouldn't want to go through the scheduler with PAN clear". > > On x86, we might as well check DF at the same time as AC. > >
hpa is right, though — calling into tracing code with AC set is not really so good. And calling schedule() (via preempt_enable() or whatever) is also bad because it runs all the scheduler code with AC on. Admittedly, the scheduler is not *that* interesting of an attack surface.
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