[ 3.5.y.z extended stable ] Patch "perf/x86/intel/lbr: Fix LBR filter" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    perf/x86/intel/lbr: Fix LBR filter

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 0a0482e443ce13cf68b7b3f40eac34d5b2a3546c Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <a.p.zijlstra at chello.nl>
Date: Fri, 3 May 2013 14:11:24 +0200
Subject: [PATCH] perf/x86/intel/lbr: Fix LBR filter

commit 6e15eb3ba6c0249c9e8c783517d131b47db995ca upstream.

The LBR 'from' adddress is under full userspace control; ensure
we validate it before reading from it.

Note: is_module_text_address() can potentially be quite
expensive; for those running into that with high overhead
in modules optimize it using an RCU backed rb-tree.

Reported-by: Andi Kleen <ak at linux.intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra at chello.nl>
Cc: eranian at google.com
Link: http://lkml.kernel.org/r/20130503121256.158211806@chello.nl
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Link: http://lkml.kernel.org/n/tip-mk8i82ffzax01cnqo829iy1q@git.kernel.org
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 520b426..62a93a4 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -442,8 +442,18 @@ static int branch_type(unsigned long from, unsigned long to)
 			return X86_BR_NONE;

 		addr = buf;
-	} else
-		addr = (void *)from;
+	} else {
+		/*
+		 * The LBR logs any address in the IP, even if the IP just
+		 * faulted. This means userspace can control the from address.
+		 * Ensure we don't blindy read any address by validating it is
+		 * a known text address.
+		 */
+		if (kernel_text_address(from))
+			addr = (void *)from;
+		else
+			return X86_BR_NONE;
+	}

 	/*
 	 * decoder needs to know the ABI especially
--
1.8.1.2