From: Andrew Jones <drjones@redhat.com>

Fix a QEMU NULL derefence that occurs when the guest attempts to
enable PMU counters with a non-v8 cpu model or a v8 cpu model
which has not configured a PMU.

Fixes: 4e7beb0cc0f3 ("target/arm: Add a timer to predict PMU counter overflow")
Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190322162333.17159-2-drjones@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index c8d3c213b6b..fc73488f6cc 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -1259,6 +1259,10 @@ static bool pmu_counter_enabled(CPUARMState *env, uint8_t counter)
     int el = arm_current_el(env);
     uint8_t hpmn = env->cp15.mdcr_el2 & MDCR_HPMN;
 
+    if (!arm_feature(env, ARM_FEATURE_PMU)) {
+        return false;
+    }
+
     if (!arm_feature(env, ARM_FEATURE_EL2) ||
             (counter < hpmn || counter == 31)) {
         e = env->cp15.c9_pmcr & PMCRE;
-- 
2.20.1