target/arm: Implement v8.1M PXN extension

In v8.1M the PXN architecture extension adds a new PXN bit to the
MPU_RLAR registers, which forbids execution of code in the region
from a privileged mode.

This is another feature which is just in the generic "in v8.1M" set
and has no ID register field indicating its presence.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201119215617.29887-3-peter.maydell@linaro.org

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 38cd35c049292d40df5a35854f4b1c2be49e946e..7b8bcd69030f886eaa0760ef2c4196dd5d196c4c 100644 (file)
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -11754,6 +11754,11 @@ bool pmsav8_mpu_lookup(CPUARMState *env, uint32_t address,
     } else {
         uint32_t ap = extract32(env->pmsav8.rbar[secure][matchregion], 1, 2);
         uint32_t xn = extract32(env->pmsav8.rbar[secure][matchregion], 0, 1);
+        bool pxn = false;
+
+        if (arm_feature(env, ARM_FEATURE_V8_1M)) {
+            pxn = extract32(env->pmsav8.rlar[secure][matchregion], 4, 1);
+        }
 
         if (m_is_system_region(env, address)) {
             /* System space is always execute never */
@@ -11761,7 +11766,7 @@ bool pmsav8_mpu_lookup(CPUARMState *env, uint32_t address,
         }
 
         *prot = simple_ap_to_rw_prot(env, mmu_idx, ap);
-        if (*prot && !xn) {
+        if (*prot && !xn && !(pxn && !is_user)) {
             *prot |= PAGE_EXEC;
         }
         /* We don't need to look the attribute up in the MAIR0/MAIR1