linux-kernel - Re: [patch 02/10] x86/mce: Disable tracing and kprobes on do_machine

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Message-ID: <20200226132850.GX18400@hirez.programming.kicks-ass.net>
Date:   Wed, 26 Feb 2020 14:28:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [patch 02/10] x86/mce: Disable tracing and kprobes on
 do_machine_check()

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.