Messages in this thread |  | | Date | Mon, 24 Feb 2014 19:49:30 -0800 | From | "H. Peter Anvin" <> | Subject | Re: perf_fuzzer compiled for x32 causes reboot |
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On 02/24/2014 11:30 AM, Peter Zijlstra wrote: > On Mon, Feb 24, 2014 at 02:13:29PM -0500, Steven Rostedt wrote: >> Ah, and x86_64 saves off the cr2 register when entering NMI and restores >> it before returning. But it seems to be missing from the i386 code. > > arch/x86/kernel/nmi.c: > > #define nmi_nesting_preprocess(regs) \ > do { \ > if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { \ > this_cpu_write(nmi_state, NMI_LATCHED); \ > return; \ > } \ > this_cpu_write(nmi_state, NMI_EXECUTING); \ > this_cpu_write(nmi_cr2, read_cr2()); \ > } while (0); \ > nmi_restart: > > #define nmi_nesting_postprocess() \ > do { \ > if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \ > write_cr2(this_cpu_read(nmi_cr2)); \ > if (this_cpu_dec_return(nmi_state)) \ > goto nmi_restart; \ > } while (0) > > That very much looks like saving/restoring CR2 to me. > > FWIW; I hate how the x86_64 and i386 versions of this NMI nesting magic > are so completely different.
Is there any way that nmi_cr2 can end up getting overwritten by multiple nestings of some kind? I would have thought it would have made more sense to spill cr2 onto the stack after the stack has been properly set up.
-hpa
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