From: "hpanvin@gmail.com" <hpa@zytor.com>
To: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determine nested NMI
Date: Sun, 19 Feb 2012 05:46:13 -0800 [thread overview]
Message-ID: <0e44abc3-f1a9-4c5b-88a8-baa563f57067@email.android.com> (raw)
In-Reply-To: <20120219125601.GD25900@elte.hu>
Vsyscall page, not vdso...
Ingo Molnar <mingo@elte.hu> wrote:
>
>* Steven Rostedt <rostedt@goodmis.org> 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 <srostedt@redhat.com>
>> 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 <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..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.
next prev parent reply other threads:[~2012-02-19 13:46 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 [this message]
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
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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