Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753581AbbGXINk (ORCPT ); Fri, 24 Jul 2015 04:13:40 -0400 Received: from casper.infradead.org ([85.118.1.10]:55439 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750990AbbGXINh (ORCPT ); Fri, 24 Jul 2015 04:13:37 -0400 Date: Fri, 24 Jul 2015 10:13:26 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: Andy Lutomirski , Steven Rostedt , X86 ML , "linux-kernel@vger.kernel.org" , Willy Tarreau , Borislav Petkov , Thomas Gleixner , Brian Gerst Subject: Re: Dealing with the NMI mess Message-ID: <20150724081326.GO25159@twins.programming.kicks-ass.net> References: <20150723173105.6795c0dc@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1052 Lines: 26 On Thu, Jul 23, 2015 at 02:59:56PM -0700, Linus Torvalds wrote: > Hmmm. I thought watchpoints were "before the instruction" too, but > that's just because I haven't used them in ages, and I didn't remember > the details. I just looked it up. > > You're right - the memory watchpoints trigger after the instruction > has executed, so RF isn't an issue. So yes, the only issue is > instruction breakpoints, and those are the only ones we need to clear. > > And that makes it really easy. > > So yes, I agree. We only need to clear all kernel breakpoints. But but but, we can access userspace with !IF, imagine someone doing: local_irq_disable(); copy_from_user_inatomic(); and as luck would have it, there's a breakpoint on the user memory we just touched. And we go and disable a user breakpoint. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/