linux-kernel - Re: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation

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Message-ID: <87h7wiznl7.fsf@nanos.tec.linutronix.de>
Date:   Thu, 14 May 2020 14:51:32 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation

Peter Zijlstra <peterz@...radead.org> writes:
> On Wed, May 13, 2020 at 09:57:52PM -0700, Andy Lutomirski wrote:
>> On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>> >
>> > From: Peter Zijlstra <peterz@...radead.org>
>> >
>> > Use arch_atomic_*() and READ_ONCE_NOCHECK() to ensure nothing untoward
>> > creeps in and ruins things.
>> >
>> > That is; this is the INT3 text poke handler, strictly limit the code
>> > that runs in it, lest it inadvertenly hits yet another INT3.
>> 
>> 
>> Acked-by: Andy Lutomirski <luto@...nel.org>
>> 
>> Does objtool catch this error?
>
> It does not. I'll put it on the (endless) todo list..

Well, at least it detects when that code calls out into something which
is not in the non-instrumentable section.

As long as instrumentation respects the rules that this section is taboo,
this should not happen. Emphasis on *should*.