Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754029Ab2BSNqo (ORCPT ); Sun, 19 Feb 2012 08:46:44 -0500 Received: from terminus.zytor.com ([198.137.202.10]:54211 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753188Ab2BSNqn (ORCPT ); Sun, 19 Feb 2012 08:46:43 -0500 References: <1329617173.1561.5.camel@acer.local.home> <20120219125601.GD25900@elte.hu> User-Agent: K-9 Mail for Android In-Reply-To: <20120219125601.GD25900@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determine nested NMI From: "hpanvin@gmail.com" Date: Sun, 19 Feb 2012 05:46:13 -0800 To: Ingo Molnar , Steven Rostedt CC: linux-kernel@vger.kernel.org, Andrew Morton , Peter Zijlstra Message-ID: <0e44abc3-f1a9-4c5b-88a8-baa563f57067@email.android.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3056 Lines: 99 Vsyscall page, not vdso... Ingo Molnar wrote: > >* Steven Rostedt wrote: > >> Ingo, >> >> I found that it is possible for userspace to prevent an NMI >> from triggering while it is running by setting its stack >> pointer to that of the NMI stack. This tricks the NMI nested >> algorithm in thinking that the NMI is nested. The easy >> solution to this is to test the %rip to make sure that the NMI >> happened in kernel mode before testing for nesting. > >Ouch... > >> I've tested a program that exhibits the missing NMIs and this >> patch corrects that behavior. > >Does it need a -stable tag? > >> Please pull the latest tip/perf/urgent tree, which can be >> found at: >> >> >git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git >> tip/perf/urgent >> >> Head SHA1: b80ddc7b1636474297815d47fbfed7552f9b8f2c >> >> >> Steven Rostedt (1): >> x86: Test saved %rip in NMI to determine nested NMI >> >> ---- >> arch/x86/kernel/entry_64.S | 8 ++++++++ >> 1 files changed, 8 insertions(+), 0 deletions(-) >> --------------------------- >> commit b80ddc7b1636474297815d47fbfed7552f9b8f2c >> Author: Steven Rostedt >> Date: Sat Feb 18 20:26:52 2012 -0500 >> >> x86: Test saved %rip in NMI to determine nested NMI >> >> Currently, the NMI handler tests if it is nested by checking the >> special variable saved no the stack (set during NMI handling) and >> whether the saved stack is the NMI stack as well (to prevent the >race >> when the variable is set to zero). But userspace may set their >%rsp >> to any value as long as the do not derefence it, and it may make >it >> point to the NMI stack, which will prevent NMIs from triggering >while >> the userspace app is running. (I tested this, and it is indeed >the case) >> >> Add another check to determine nested NMIs by looking at the >saved >> %rip and making sure that it is a kernel pointer (negative). >> >> Cc: H. Peter Anvin >> Signed-off-by: Steven Rostedt >> >> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S >> index 3fe8239..7c35a7a 100644 >> --- a/arch/x86/kernel/entry_64.S >> +++ b/arch/x86/kernel/entry_64.S >> @@ -1532,6 +1532,14 @@ ENTRY(nmi) >> pushq_cfi %rdx >> >> /* >> + * If the RIP is not negative then we are in userspace where this >is not >> + * a nested NMI. >> + */ >> + movq 8(%rsp), %rdx >> + testq %rdx, %rdx >> + jns first_nmi > >Does this do the right thing for the vDSO as well? It is in >negative addresses: > >ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 > [vsyscall] > >Thanks, > > Ingo -- Sent from my Android phone with K-9 Mail. Please excuse my brevity. -- 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/