On Wed, Jul 29, 2015 at 10:57:26AM -0700, Andy Lutomirski wrote:
> OK if I do that as a follow-up? It would probably want to be a
> separate patch anyway.
Of course.
> Hmm, I'm starting to like this new regime in which we never ever
> switch to user mode from anywhere other than the standard kernel
> stack. It looks like even Xen may play along and do it cleanly soon
> :) Maybe I'll even add an assertion somewhere to make sure we don't
> break it. (I think this also means that the bad iret fixup can be
> simplified.)
Definitely sounds like a nice, logical thing. We sometimes switch stacks
to land on the kernel stack before returning to user mode (IST and all)
but I guess that's a clean enough thing to do. Oh, and only a couple of
insns so yeah.
> Also, with all this stuff applied (and the modify_ldt thing, once the
> Xen folks figure out what's wrong), I think we can reinstate the old
> LARL check for 16-bit segments and thus prevent naughty users from
> banging on espfix using only sigreturn.
Uuh, and then only check ZF. I guess this should cover all the legacy
cases, which is nice.
Yeah, sounds coolio. :-)
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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