linux-kernel - Re: kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter() with nmi

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Message-ID: <20210129175943.GH8912@worktop.programming.kicks-ass.net>
Date:   Fri, 29 Jan 2021 18:59:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nikolay Borisov <nborisov@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter()
 with nmi_enter()")

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?