linux-kernel - Re: Dealing with the NMI 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: <20150724195509.GM2859@worktop.programming.kicks-ass.net>
Date:	Fri, 24 Jul 2015 21:55:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Willy Tarreau <w@....eu>, Steven Rostedt <rostedt@...dmis.org>,
	Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Dealing with the NMI mess

On Fri, Jul 24, 2015 at 11:29:29AM -0700, Linus Torvalds wrote:
> On Fri, Jul 24, 2015 at 8:30 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Fri, Jul 24, 2015 at 05:26:37PM +0200, Willy Tarreau wrote:
> >> >
> >> > The point is, if we trigger a #DB on an instruction breakpoint
> >> > while !IF, then we simply disable that breakpoint and do the RET.
> >>
> >> Yes but the breakpoint remains disabled then. Or I'm missing
> >> something.
> >
> > http://marc.info/?l=linux-kernel&m=143773601130974
> >
> > We re-enable before going back to userspace.
> 
> Actually, Andy had a good argument that we don't even need this.
> 
> We just don't ever need to disable data breakpoints. Even if we end up doing
> 
>         cli();
>         copy_from_user_inatomic();
> 
> that actually works fine. If there are data breakpoints, we will have

I worry that we'll end up running the do_debug() handlers from effective
NMI context.

The NMI might have preempted locks which these handlers require etc..
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/