From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Nikolay Borisov <nborisov@suse.com>,
LKML <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter() with nmi_enter()")
Date: Tue, 2 Feb 2021 19:30:34 +0100 [thread overview]
Message-ID: <YBmaStZn9XEU0QE+@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210202115623.08e8164d@gandalf.local.home>
On Tue, Feb 02, 2021 at 11:56:23AM -0500, Steven Rostedt wrote:
> NMIs are special, and they always have been. They shouldn't be doing much
> anyway. If they are, then that's a problem.
There is a fair amount of NMI level code these days, and it seems to be
ever increasing...
> My question wasn't to have them do it, I was simply asking if they do. I
> was assuming that they do not.
per nmi_enter() we do:
__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
> > But it doesn't help with:
> >
> > spin_lock_irq(&foo); // task context
> > #DB
> > spin_lock_irq(&foo); // interrupt context per your above
>
> The statement above said:
>
> "If #DB and #BP do not change the in_interrupt() context"
>
> Which would make the above be in the same context and the handler would
> not be called for the #DB case.
But then replace the above #DB with __fentry__ and explain how it is
fundamentally different? And consider that direct call into god knows
what code option you have. That doesn't go past any recursion checks
IIRC.
> I'm fine with #DB and #BP being a "in_nmi()", as they are probably even
> more special than NMIs.
That does mean that kprobes are then fundamentally running from
in_nmi(), which is what started all this.
Sure, the opt-probes and ftrace-probes don't actually have in_nmi() set
today (because they don't trigger an exception), but given that that is
all optional, any kprobe handler had better be in_nmi() clean.
next prev parent reply other threads:[~2021-02-02 18:33 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <25cd2608-03c2-94b8-7760-9de9935fde64@suse.com>
[not found] ` <20210128001353.66e7171b395473ef992d6991@kernel.org>
[not found] ` <20210128002452.a79714c236b69ab9acfa986c@kernel.org>
[not found] ` <a35a6f15-9ab1-917c-d443-23d3e78f2d73@suse.com>
[not found] ` <20210128103415.d90be51ec607bb6123b2843c@kernel.org>
2021-01-28 3:38 ` kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter() with nmi_enter()") Masami Hiramatsu
2021-01-28 7:11 ` Nikolay Borisov
2021-01-28 16:12 ` Nikolay Borisov
2021-01-28 16:45 ` Nikolay Borisov
2021-01-28 16:50 ` Josh Poimboeuf
2021-01-28 21:52 ` [PATCH] x86: Disable CET instrumentation in the kernel Josh Poimboeuf
2021-01-29 6:23 ` Nikolay Borisov
2021-01-29 10:21 ` Borislav Petkov
[not found] ` <20210129151034.iba4eaa2fuxsipqa@treble>
2021-01-29 16:30 ` Borislav Petkov
2021-01-29 16:49 ` Josh Poimboeuf
2021-01-29 16:54 ` Nikolay Borisov
2021-01-29 17:03 ` Josh Poimboeuf
2021-01-29 17:07 ` Borislav Petkov
2021-01-29 17:58 ` Seth Forshee
2021-01-28 18:24 ` kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter() with nmi_enter()") Peter Zijlstra
2021-01-29 1:34 ` Alexei Starovoitov
2021-01-29 6:36 ` Nikolay Borisov
[not found] ` <YBPNyRyrkzw2echi@hirez.programming.kicks-ass.net>
[not found] ` <20210129224011.81bcdb3eba1227c414e69e1f@kernel.org>
[not found] ` <20210129105952.74dc8464@gandalf.local.home>
2021-01-29 16:24 ` Peter Zijlstra
2021-01-29 17:45 ` Alexei Starovoitov
2021-01-29 17:59 ` Peter Zijlstra
2021-01-29 19:01 ` Steven Rostedt
2021-01-29 21:05 ` Alexei Starovoitov
2021-01-30 1:41 ` Masami Hiramatsu
2021-01-29 21:24 ` Steven Rostedt
2021-01-30 8:28 ` Peter Zijlstra
2021-01-30 12:44 ` Steven Rostedt
2021-02-02 10:45 ` Peter Zijlstra
2021-02-02 14:52 ` Steven Rostedt
2021-02-02 16:45 ` Peter Zijlstra
2021-02-02 16:56 ` Steven Rostedt
2021-02-02 18:30 ` Peter Zijlstra [this message]
2021-02-02 21:05 ` Steven Rostedt
2021-02-03 13:33 ` Masami Hiramatsu
2021-02-03 13:52 ` Steven Rostedt
2021-01-30 2:02 ` Masami Hiramatsu
2021-01-30 3:08 ` Alexei Starovoitov
2021-01-30 12:10 ` Masami Hiramatsu
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