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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>
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Subject: Re: [patch V4 part 4 02/24] x86/int3: Avoid atomic instrumentation
In-Reply-To: <20200514093257.GT2978@hirez.programming.kicks-ass.net>
References: <20200505134926.578885807@linutronix.de> <20200505135313.517429268@linutronix.de> <CALCETrXVQsdPafvH56_nF+CKU94wgq-T71=EB6eSBnz70Cd0Rw@mail.gmail.com> <20200514093257.GT2978@hirez.programming.kicks-ass.net>
Date:   Thu, 14 May 2020 14:51:32 +0200
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Peter Zijlstra <peterz@infradead.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@linutronix.de> wrote:
>> >
>> > From: Peter Zijlstra <peterz@infradead.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@kernel.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*.