From: Steven Rostedt <rostedt@goodmis.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: [PATCH v2][GIT PULL][v3.3] x86: Test saved %cs in NMI to determine nested NMI
Date: Sun, 19 Feb 2012 16:43:37 -0500 [thread overview]
Message-ID: <1329687817.1561.27.camel@acer.local.home> (raw)
In-Reply-To: <20120219125601.GD25900@elte.hu>
Ingo,
I rebased the same branch so you may need to wait a little for the
kernel.org mirrors to update.
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: 38f53faa02c0976ed0a6f0290771a4cbe6dc655b
Steven Rostedt (1):
x86: Test saved %cs in NMI to determine nested NMI
----
arch/x86/kernel/entry_64.S | 7 +++++++
1 files changed, 7 insertions(+), 0 deletions(-)
---------------------------
commit 38f53faa02c0976ed0a6f0290771a4cbe6dc655b
Author: Steven Rostedt <srostedt@redhat.com>
Date: Sat Feb 18 20:26:52 2012 -0500
x86: Test saved %cs in NMI to determine nested NMI
Currently, the NMI handler tests if it is nested by checking the
special variable saved on 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 they 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
%cs (code segment register) and making sure that it is the kernel code segment.
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 3fe8239..debd851 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1532,6 +1532,13 @@ ENTRY(nmi)
pushq_cfi %rdx
/*
+ * If %cs was not the kernel segment, then the NMI triggered in user
+ * space, which means it is definitely not nested.
+ */
+ cmp $__KERNEL_CS, 16(%rsp)
+ jne first_nmi
+
+ /*
* Check the special variable on the stack to see if NMIs are
* executing.
*/
next prev parent reply other threads:[~2012-02-19 21:43 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-19 2:06 [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determine nested NMI Steven Rostedt
2012-02-19 12:56 ` Ingo Molnar
2012-02-19 13:46 ` hpanvin@gmail.com
2012-02-19 13:48 ` Ingo Molnar
2012-02-19 20:34 ` Steven Rostedt
2012-02-19 20:45 ` H. Peter Anvin
2012-02-19 21:00 ` Steven Rostedt
2012-02-19 14:57 ` Steven Rostedt
2012-02-20 8:10 ` Ingo Molnar
2012-02-20 14:41 ` Steven Rostedt
2012-02-20 15:34 ` Ingo Molnar
2012-02-20 17:07 ` H. Peter Anvin
2012-02-19 21:43 ` Steven Rostedt [this message]
2012-02-20 11:47 ` [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case tip-bot for Steven Rostedt
2012-02-20 16:51 ` Steven Rostedt
2012-02-27 21:29 ` Greg KH
2012-02-20 18:03 ` Linus Torvalds
2012-02-20 18:26 ` Steven Rostedt
2012-02-21 22:08 ` [tip:x86/urgent] x86: Specify a size for the cmp in the NMI handler tip-bot for Steven Rostedt
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