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

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Date:	Mon, 11 Jun 2012 15:44:26 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, asharma@...com, mingo@...e.hu
Subject: [PATCH] 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().

commit db0dc75d6403b6663c0eab4c6ccb672eb9b2ed72
Author: Arun Sharma <asharma@...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@...gle.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 {
--
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