linux-kernel - Re: [patch V4 part 1 35/36] x86: Replace ist_enter() with nmi

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1603808584.1778.1588875478687.JavaMail.zimbra@efficios.com>
Date:   Thu, 7 May 2020 14:17:58 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, paulmck <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>, rostedt <rostedt@...dmis.org>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch V4 part 1 35/36] x86: Replace ist_enter() with
 nmi_enter()

----- On May 7, 2020, at 2:04 PM, Andy Lutomirski luto@...nel.org wrote:

> On Tue, May 5, 2020 at 7:14 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> From: Peter Zijlstra <peterz@...radead.org>
>>
>> A few exceptions (like #DB and #BP) can happen at any location in the code,
>> this then means that tracers should treat events from these exceptions as
>> NMI-like. The interrupted context could be holding locks with interrupts
>> disabled for instance.
>>
>> Similarly, #MC is an actual NMI-like exception.
> 
> Is it permissible to send a signal from inside nmi_enter()?  I imagine
> so, but I just want to make sure.

If you mean sending a proper signal, I would guess not.

I suspect you'll rather want to use "irq_work()" from NMI context to ensure
the rest of the work (e.g. sending a signal or a wakeup) is performed from
IRQ context very soon after the NMI, rather than from NMI context.

AFAIK this is how this is done today by perf, ftrace, ebpf, and lttng.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com