On Sun, Aug 26, 2018 at 1:15 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Sun, 26 Aug 2018, Andy Lutomirski wrote: >> > On Aug 26, 2018, at 9:47 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> >> On Sun, Aug 26, 2018 at 7:20 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> >>> I tried to convince Ingo to use this method for doing "write rarely" >> >>> and he soundly rejected it. :) I've always liked this because AFAICT, >> >>> it's local to the CPU. I had proposed it in >> >>> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=kspp/write-rarely&id=9ab0cb2618ebbc51f830ceaa06b7d2182fe1a52d >> >> >> >> Ingo, can you clarify why you hate it? I personally would rather use CR3, but CR0 seems like a fine first step, at least for text_poke. >> > >> > Sorry, it looks like it was tglx, not Ingo: >> > >> > https://lkml.kernel.org/r/alpine.DEB.2.20.1704071048360.1716@nanos >> > >> > This thread is long, and one thing that I think went unanswered was >> > "why do we want this to be fast?" the answer is: for doing page table >> > updates. Page tables are becoming a bigger target for attacks now, and >> > it's be nice if they could stay read-only unless they're getting >> > updated (with something like this). >> > >> > >> It kind of sounds like tglx would prefer the CR3 approach. And indeed my >> patch has a serious problem wrt the NMI code. > > That's exactly the problem I have with CR0. It leaves everything and some > more writeable for any code which can interrupt that section. I thought the point was that the implementation I suggested was NMI-proof? (And in reading Documentation/preempt-locking.txt it sounds like disabling interrupts is redundant to preempt_disable()? But I don't understand how; it looks like the preempt stuff is advisory?) -Kees -- Kees Cook Pixel Security
