[PATCH 039/115] perf/x86/intel/lbr: Fix LBR filter

[Luis Henriques]

3.5.7.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <a.p.zijlstra at chello.nl>

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