Messages in this thread | | | Date | Sun, 01 Sep 2013 09:10:29 -0700 | From | "H. Peter Anvin" <> | Subject | Re: On the correctness of dbe3ed1c078c193be34326728d494c5c4bc115e2 |
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On 09/01/2013 08:58 AM, Linus Torvalds wrote: > On Sun, Sep 1, 2013 at 5:20 AM, H. Peter Anvin <hpa@zytor.com> wrote: >> >> This has the end result that we treat a user space instruction which >> touches a privileged data structure that then page faults (e.g. a >> segment load which causes #PF on the GDT) as a user-space fault. >> >> This seems very wrong to me, since such a #PF would indicate a serious >> error in the kernel. > > Not necessarily. Don't we basically do exactly that for the F00F bug > workaround, for example? > > Linus >
Actually, from looking at it, the F00F workaround is broken *exactly* because of this patch. By forcing PF_USER to set, we go into the if (error_code & PF_USER) branch of __bad_area_semaphore(), which means we *don't* do the F00F checking, and will deliver a SIGSEGV with the IDT address to the user space process instead of SIGILL.
-hpa
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