From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.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: Fri, 29 Jan 2021 16:24:54 -0500 [thread overview]
Message-ID: <20210129162454.293523c6@gandalf.local.home> (raw)
In-Reply-To: <20210129140103.3ce971b7@gandalf.local.home>
On Fri, 29 Jan 2021 14:01:03 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 29 Jan 2021 18:59:43 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Fri, Jan 29, 2021 at 09:45:48AM -0800, Alexei Starovoitov wrote:
> > > Same things apply to bpf side. We can statically prove safety for
> > > ftrace and kprobe attaching whereas to deal with NMI situation we
> > > have to use run-time checks for recursion prevention, etc.
> >
> > I have no idea what you're saying. You can attach to functions that are
> > called with random locks held, you can create kprobes in some very
> > sensitive places.
> >
> > What can you staticlly prove about that?
>
> I think the main difference is, if you attach a kprobe or ftrace function,
> you can theoretically analyze the location before you do the attachment.
>
> Does, the NMI context mean "in_nmi()" returns true? Because there's cases
> in ftrace callbacks where that is checked (like the stack tracer). And
> having ftrace return true for "in_nmi()" will break a lot of existing
> utilities.
Specifically, kprobe and ftrace callbacks may have this:
if (in_nmi())
return;
raw_spin_lock_irqsave(&lock, flags);
[..]
raw_spin_unlock_irqrestore(&lock, flags);
Which is totally fine to have, but the above only works if "in_nmi()"
returns true only if you are in a real NMI.
The stack tracer code does exactly the above.
-- Steve
next prev parent reply other threads:[~2021-01-29 21:25 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 [this message]
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
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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