From: Steven Rostedt <rostedt@goodmis.org>
To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org,
a.p.zijlstra@chello.nl, torvalds@linux-foundation.org,
stable@kernel.org, tglx@linutronix.de, mingo@elte.hu,
Greg KH <greg@kroah.com>
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case
Date: Mon, 20 Feb 2012 11:51:41 -0500 [thread overview]
Message-ID: <1329756701.25686.31.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <tip-45d5a1683c04be28abdf5c04c27b1417e0374486@git.kernel.org>
On Mon, 2012-02-20 at 03:47 -0800, tip-bot for Steven Rostedt wrote:
> Commit-ID: 45d5a1683c04be28abdf5c04c27b1417e0374486
> Gitweb: http://git.kernel.org/tip/45d5a1683c04be28abdf5c04c27b1417e0374486
> Author: Steven Rostedt <rostedt@goodmis.org>
> AuthorDate: Sun, 19 Feb 2012 16:43:37 -0500
> Committer: Ingo Molnar <mingo@elte.hu>
> CommitDate: Mon, 20 Feb 2012 09:09:57 +0100
>
> x86/nmi: Test saved %cs in NMI to determine nested NMI case
>
> 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.
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: <stable@kernel.org>
Just so that we do not confuse Greg, the bug was introduced in the 3.3
merge window. It does not exist in 3.2 or earlier.
-- Steve
> Link: http://lkml.kernel.org/r/1329687817.1561.27.camel@acer.local.home
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
> arch/x86/kernel/entry_64.S | 7 +++++++
> 1 files changed, 7 insertions(+), 0 deletions(-)
>
> 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:[~2012-02-20 16:51 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 ` [PATCH v2][GIT PULL][v3.3] x86: Test saved %cs " Steven Rostedt
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 [this message]
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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