[PATCH] perf/x86: fix broken LBR fixup code

[PATCH] perf/x86: fix broken LBR fixup code

[Stephane Eranian]

I noticed that the LBR fixups were not working anymore
on programs where they used to. I tracked this down to
a recent change to copy_from_user_nmi().

commit db0dc75d6403b6663c0eab4c6ccb672eb9b2ed72
Author: Arun Sharma <asharma@fb.com>
Date:   Fri Apr 20 15:41:36 2012 -0700

    perf/x86: Check user address explicitly in copy_from_user_nmi()
    
This commit added a call to __range_not_ok() to the
copy_from_user_nmi() routine. The problem is that the logic
of the test must be reversed. __range_not_ok() returns 0 if the
range is VALID. We want to return early from copy_from_user_nmi()
if the range is NOT valid.

Signed-off-by: Stephane Eranian <eranian@google.com>
---

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 677b1ed..4f74d94 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -22,7 +22,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 	void *map;
 	int ret;
 
-	if (__range_not_ok(from, n, TASK_SIZE) == 0)
+	if (__range_not_ok(from, n, TASK_SIZE))
 		return len;
 
 	do {

Re: [PATCH] perf/x86: fix broken LBR fixup code

[Peter Zijlstra]

On Mon, 2012-06-11 at 15:44 +0200, Stephane Eranian wrote:
> I noticed that the LBR fixups were not working anymore
> on programs where they used to. I tracked this down to
> a recent change to copy_from_user_nmi().
> 
> commit db0dc75d6403b6663c0eab4c6ccb672eb9b2ed72
> Author: Arun Sharma <asharma@fb.com>
> Date:   Fri Apr 20 15:41:36 2012 -0700
> 
>     perf/x86: Check user address explicitly in copy_from_user_nmi()
>     
> This commit added a call to __range_not_ok() to the
> copy_from_user_nmi() routine. The problem is that the logic
> of the test must be reversed. __range_not_ok() returns 0 if the
> range is VALID. We want to return early from copy_from_user_nmi()
> if the range is NOT valid.

D'0h.. Thanks!

Re: [PATCH] perf/x86: fix broken LBR fixup code

[Arun Sharma]

On 6/11/12 6:47 AM, Peter Zijlstra wrote:
> On Mon, 2012-06-11 at 15:44 +0200, Stephane Eranian wrote:
>> I noticed that the LBR fixups were not working anymore
>> on programs where they used to. I tracked this down to
>> a recent change to copy_from_user_nmi().
>>
>> commit db0dc75d6403b6663c0eab4c6ccb672eb9b2ed72
>> Author: Arun Sharma<asharma@fb.com>
>> Date:   Fri Apr 20 15:41:36 2012 -0700
>>
>>      perf/x86: Check user address explicitly in copy_from_user_nmi()
>>
>> This commit added a call to __range_not_ok() to the
>> copy_from_user_nmi() routine. The problem is that the logic
>> of the test must be reversed. __range_not_ok() returns 0 if the
>> range is VALID. We want to return early from copy_from_user_nmi()
>> if the range is NOT valid.
>
> D'0h.. Thanks!

My bad. I was fooled by all the kernel addresses that were unwound 
properly. Didn't notice the broken unwinding in user space before I sent 
the patch. The fix looks good. Thanks.

  -Arun

[tip:perf/urgent] perf/x86: Fix broken LBR fixup code

[tip-bot for Stephane Eranian]

Commit-ID:  25f42985825dd93f0593efe454e54c2aa13f7830
Gitweb:     http://git.kernel.org/tip/25f42985825dd93f0593efe454e54c2aa13f7830
Author:     Stephane Eranian <eranian@google.com>
AuthorDate: Mon, 11 Jun 2012 15:44:26 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Jun 2012 15:00:28 +0200

perf/x86: Fix broken LBR fixup code

I noticed that the LBR fixups were not working anymore
on programs where they used to. I tracked this down to
a recent change to copy_from_user_nmi():

 db0dc75d640 ("perf/x86: Check user address explicitly in copy_from_user_nmi()")

This commit added a call to __range_not_ok() to the
copy_from_user_nmi() routine. The problem is that the logic
of the test must be reversed. __range_not_ok() returns 0 if the
range is VALID. We want to return early from copy_from_user_nmi()
if the range is NOT valid.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Arun Sharma <asharma@fb.com>
Link: http://lkml.kernel.org/r/20120611134426.GA7542@quad
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/lib/usercopy.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 677b1ed..4f74d94 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -22,7 +22,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 	void *map;
 	int ret;
 
-	if (__range_not_ok(from, n, TASK_SIZE) == 0)
+	if (__range_not_ok(from, n, TASK_SIZE))
 		return len;
 
 	do {