From 6e15eb3ba6c0249c9e8c783517d131b47db995ca Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri, 3 May 2013 14:11:24 +0200
Subject: [PATCH] perf/x86/intel/lbr: Fix LBR filter
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@linux.intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/20130503121256.158211806@chello.nl
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/n/tip-mk8i82ffzax01cnqo829iy1q@git.kernel.org
---
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 da02e9cc3754..de341d4ec92a 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
--
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