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

1 files 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