linux-kernel - Re: [RFC] #MC mess

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: <20200218181734.703038e1@gandalf.local.home>
Date:   Tue, 18 Feb 2020 18:17:34 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "Luck, Tony" <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, x86-ml <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] #MC mess

On Tue, 18 Feb 2020 15:10:17 -0800
Andy Lutomirski <luto@...capital.net> wrote:

> > On Feb 18, 2020, at 10:20 AM, Luck, Tony <tony.luck@...el.com> wrote:
> > 
> >   
> >> 
> >> Anything else I'm missing? It is likely...  
> > 
> > +    hw_breakpoint_disable();
> > +    static_key_disable(&__tracepoint_read_msr.key);
> > +    tracing_off();
> > +
> >    ist_enter(regs);
> > 
> > How about some code to turn all those back on for a recoverable (where we actually recovered) #MC?
> > 
> >   
> 
> 
> At the very least, in the user_mode(regs) case, tracing is fine.

Also, I don't think "tracing_off()" is what is wanted here. That just
disables writing to the ring buffer, which can be called in pretty much
any context (if it's before in_nmi() get's set, the worse thing that
happens is that events will get dropped due to the recursion protection
that checks to make sure there's no re-entrant events at the same level
of context).

The only issue with having function tracing enabled, is that it may add
a breakpoint when it gets turned on or off. And that tracing_off()
doesn't prevent that.

tracepoints still use RCU of some kind, and the protection there has
nothing to do with whether a trace point does recording or not.

-- Steve