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: <20150724120249.1ba0d9de@gandalf.local.home>
Date:	Fri, 24 Jul 2015 12:02:49 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Willy Tarreau <w@....eu>, Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Dealing with the NMI mess

On Fri, 24 Jul 2015 08:48:57 -0700
Andy Lutomirski <luto@...capital.net> wrote:

> So by the time we detect that we've hit a watchpoint, the instruction
> that tripped it is done and we don't need RF.  Furthermore, after
> reading 17.3.1.1: I *think* that regs->flags withh have RF *clear* if
> we hit a watchpoint.  So this might be as simple as:
> 
> if ((dr6 && (0xf * DR_TRAP0) && (regs->flags & (X86_EFLAGS_RF |

Um, isn't 0xf * DR_TRAP0 same as a constant "true"?

-- Steve


> X86_EFLAGS_IF)) == X86_EFLAGS_RF && !user_mode(regs))
>   for (i = 0; i < 4; i++)
>     if (dr6 & (DR_TRAP0<<i)) {
>       /* hit a kernel breakpoint with IF clear */
>       dr7 &= ~(DR_GLOBAL_ENABLE << (i * DR_ENABLE_SHIFT));
>     }
> 
> I'm not saying that your code is wrong, but I think this is simpler
> and avoids poking at yet more per-cpu state from NMI context, which is
> kind of nice.
> 
> If you don't like the RF games above, it would also be straightforward
> to parse dr0..dr3 for each DR_TRAP bit that's set and see if it's a
> breakpoint.
> 
> --Andy

--
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/