target/arm: Permit accesses to ELR_Hyp from Hyp mode via MSR/MRS (banked)

The MSR (banked) and MRS (banked) instructions allow accesses to ELR_Hyp
from either Monitor or Hyp mode. Our translate time check
was overly strict and only permitted access from Monitor mode.

The runtime check we do in msr_mrs_banked_exc_checks() had the
correct code in it, but never got there because of the earlier
"currmode == tgtmode" check. Special case ELR_Hyp.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Message-id: 20180814124254.5229-9-peter.maydell@linaro.org

2 files changed, 18 insertions, 14 deletions

diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c
index d550978..952b8d1 100644
--- a/target/arm/op_helper.c
+++ b/target/arm/op_helper.c
@@ -611,6 +611,14 @@ static void msr_mrs_banked_exc_checks(CPUARMState *env, uint32_t tgtmode,
      */
     int curmode = env->uncached_cpsr & CPSR_M;
 
+    if (regno == 17) {
+        /* ELR_Hyp: a special case because access from tgtmode is OK */
+        if (curmode != ARM_CPU_MODE_HYP && curmode != ARM_CPU_MODE_MON) {
+            goto undef;
+        }
+        return;
+    }
+
     if (curmode == tgtmode) {
         goto undef;
     }
@@ -638,17 +646,9 @@ static void msr_mrs_banked_exc_checks(CPUARMState *env, uint32_t tgtmode,
     }
 
     if (tgtmode == ARM_CPU_MODE_HYP) {
-        switch (regno) {
-        case 17: /* ELR_Hyp */
-            if (curmode != ARM_CPU_MODE_HYP && curmode != ARM_CPU_MODE_MON) {
-                goto undef;
-            }
-            break;
-        default:
-            if (curmode != ARM_CPU_MODE_MON) {
-                goto undef;
-            }
-            break;
+        /* SPSR_Hyp, r13_hyp: accessible from Monitor mode only */
+        if (curmode != ARM_CPU_MODE_MON) {
+            goto undef;
         }
     }
 
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 14aa2cd..8405c08 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -4506,10 +4506,14 @@ static bool msr_banked_access_decode(DisasContext *s, int r, int sysm, int rn,
         }
         break;
     case ARM_CPU_MODE_HYP:
-        /* Note that we can forbid accesses from EL2 here because they
-         * must be from Hyp mode itself
+        /*
+         * SPSR_hyp and r13_hyp can only be accessed from Monitor mode
+         * (and so we can forbid accesses from EL2 or below). elr_hyp
+         * can be accessed also from Hyp mode, so forbid accesses from
+         * EL0 or EL1.
          */
-        if (!arm_dc_feature(s, ARM_FEATURE_EL2) || s->current_el < 3) {
+        if (!arm_dc_feature(s, ARM_FEATURE_EL2) || s->current_el < 2 ||
+            (s->current_el < 3 && *regno != 17)) {
             goto undef;
         }
         break;