Messages in this thread |  | | From | Andy Lutomirski <> | Date | Wed, 26 Feb 2020 07:10:01 -0800 | Subject | Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine_check() |
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On Wed, Feb 26, 2020 at 5:28 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Feb 25, 2020 at 09:29:00PM -0800, Andy Lutomirski wrote: > > > >> +void notrace do_machine_check(struct pt_regs *regs, long error_code) > > >> { > > >> DECLARE_BITMAP(valid_banks, MAX_NR_BANKS); > > >> DECLARE_BITMAP(toclear, MAX_NR_BANKS); > > >> @@ -1360,6 +1366,7 @@ void do_machine_check(struct pt_regs *re > > >> ist_exit(regs); > > >> } > > >> EXPORT_SYMBOL_GPL(do_machine_check); > > >> +NOKPROBE_SYMBOL(do_machine_check); > > > > > > That won't protect all the function called by do_machine_check(), right? > > > There are lots of them. > > > > > > > It at least means we can survive to run actual C code in > > do_machine_check(), which lets us try to mitigate this issue further. > > PeterZ has patches for that, and maybe this series fixes it later on. > > (I'm reading in order!) > > Yeah, I don't cover that either. Making the kernel completely kprobe > safe is _lots_ more work I think. > > We really need some form of automation for this :/ The current situation > is completely nonsatisfactory.
I've looked at too many patches lately and lost track a bit of which is which. Shouldn't a simple tracing_disable() or similar in do_machine_check() be sufficient? We'd maybe want automation to check everything before it. We still need to survive hitting a kprobe int3, but that shouldn't have recursion issues.
(Yes, that function doesn't exist in current kernels. And we'd need to make sure that BPF respects it.)
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