Messages in this thread | | | From | Andrew Lutomirski <> | Date | Sun, 29 May 2011 15:57:05 -0400 | Subject | Re: [PATCH 4/5] x86-64: Replace vsyscall gettimeofday fallback with int 0xcc |
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On Sun, May 29, 2011 at 3:49 PM, Ingo Molnar <mingo@elte.hu> wrote: > > * Andrew Lutomirski <luto@mit.edu> wrote: > >> > Ok, i suspect you marked it 0xCC because that's the INT3 instruction >> > - not very useful for exploits? >> >> Exactly. >> >> The comments in irq_vectors.h make it sound like vectors 0x81..0xed >> are used for device interrupts but AFAICT it's only 0x20..0x39 that >> are used, so the precise choice of vector doesn't matter that much. > > No, we use almost all of the vector space for device interrupts. Why > do you think only 0x20..0x39 is used?
Possibility my inability to understand all the IRQ mapping code in just half an hour of trying.
In arch/x86/kernel/irq.c, arch_probe_nr_irqs returns NR_IRQS_LEGACY, which I think means that the genirq code allocates will only expect IRQs on that many vectors.
If I'm wrong then my patch could be bad: if something tries to use vector 0xcc for a device interrupt, then the vsyscall emulation code will eat that interrupt.
(0xcc is barely below the maximum. INVALIDATE_TLB_VECTOR_START could be as low as 0xcf.)
--Andy
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