Messages in this thread |  | | From | Linus Torvalds <> | Date | Thu, 2 Jul 2020 12:52:27 -0700 | Subject | Re: objtool clac/stac handling change.. |
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On Thu, Jul 2, 2020 at 6:32 AM Michael Ellerman <mpe@ellerman.id.au> wrote: > > Probably the simplest option for us is to just handle it in our > unsafe_op_wrap(). I'll try and come up with something tomorrow.
IMy suggestion was to basically just always handle it in all exception cases.
And note that IU don't mean the fault handler: obviously page faults (or unaligned faults or whatever) can happen while in a user access region.
But I mean any time fixup_exception() triggers.
For x86, this is in fact particularly natural: it involves just always clearing the AC bit in the "struct pt_regs" that fixup_exception() gets anyway. We can do it without even bothering with checking for CLAC/STAC support, since without it, AC is meaningless in kernel mode anyway, but also because doing "user_access_end()" in the exception would be pointless: AC is restored by the exception routine, so on x86 you *have* to do it by just modifying the return state.
Linus
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