Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 5 Mar 2018 10:23:59 -0800 | Subject | Re: [PATCH 07/34] x86/entry/32: Restore segments before int registers |
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On Mon, Mar 5, 2018 at 5:12 AM, Joerg Roedel <joro@8bytes.org> wrote: > >> The things is, we *know* that we will restore two segment registers with the >> user cr3 already loaded: CS and SS get restored with the final iret. > > Yeah, I know, but the iret-exception path is fine because it will > deliver a SIGILL and doesn't return to the faulting iret.
That's not so much my worry, as just getting %cr3 wrong. The fact is, we still take the exception, and we still have to handle it, and that still needs to get the user<->kernel cr3 right.
So then the whole "restore segments early" must be wrong, because *that* path must get it all right too, no?
And it appears that the code *does* get it right, and you can just avoid this patch entirely?
> The iret-exception case is tested by the ldt_gdt selftest (the > do_multicpu_tests subtest). But I didn't actually tested single-stepping > through sysenter yet. I just re-ran the same tests I did with v2 on this > patch-set.
Ok. Maybe we should have a test for the "take DB on first instruction of sysenter".
Linus
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