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Subject[PATCH 2/3] perf, x86, 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 either stop using modules as
all sane people do or optimize it using an RCU backed rb-tree.

Reported-by: Andi Kleen <ak@linux.intel.com>
Cc: eranian@google.com
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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(-)

--- 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 fro
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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