Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 5 Mar 2018 13:58:32 -0800 | Subject | Re: [PATCH 07/34] x86/entry/32: Restore segments before int registers |
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On Mon, Mar 5, 2018 at 1:35 PM, Joerg Roedel <joro@8bytes.org> wrote: > On Mon, Mar 05, 2018 at 12:50:33PM -0800, Linus Torvalds wrote: >> >> Ahh, good. So presumably Joerg actually did check it, just didn't even notice ;) > > Yeah, sort of. I ran the test, but it didn't catch the failure case in > previous versions which was return to user with kernel-cr3 :)
Ahh. Yes, that's bad. The NX protection to guarantee that you don't return to user mode was really good on x86-64.
So some other case could slip through, because user code can happily run with the kernel page tables.
> I could probably add some debug instrumentation to check for that in my > future testing, as there is no NX protection in the user address-range > for the kernel-cr3.
Does not NX work with PAE?
Oh, it looks like the NX bit is marked as "RSVD (must be 0)" in the PDPDT. Oh well.
Linux
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