target/riscv/pmp: Raise exception if no PMP entry is configured

As per the privilege specification, any access from S/U mode should fail
if no pmp region is configured.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20201223192553.332508-1-atish.patra@wdc.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/op_helper.c

@@ -150,6 +150,11 @@ target_ulong helper_mret(CPURISCVState *env, target_ulong cpu_pc_deb)
 
     uint64_t mstatus = env->mstatus;
     target_ulong prev_priv = get_field(mstatus, MSTATUS_MPP);
+
+    if (!pmp_get_num_rules(env) && (prev_priv != PRV_M)) {
+        riscv_raise_exception(env, RISCV_EXCP_ILLEGAL_INST, GETPC());
+    }
+
     target_ulong prev_virt = get_field(env->mstatus, MSTATUS_MPV);
     mstatus = set_field(mstatus, MSTATUS_MIE,
                         get_field(mstatus, MSTATUS_MPIE));

target/riscv/pmp.c

@@ -74,7 +74,7 @@ static inline int pmp_is_locked(CPURISCVState *env, uint32_t pmp_index)
 /*
  * Count the number of active rules.
  */
-static inline uint32_t pmp_get_num_rules(CPURISCVState *env)
+uint32_t pmp_get_num_rules(CPURISCVState *env)
 {
      return env->pmp_state.num_rules;
 }
@@ -237,7 +237,7 @@ bool pmp_hart_has_privs(CPURISCVState *env, target_ulong addr,
 
     /* Short cut if no rules */
     if (0 == pmp_get_num_rules(env)) {
-        return true;
+        return (env->priv == PRV_M) ? true : false;
     }
 
     if (size == 0) {

target/riscv/pmp.h

@@ -64,5 +64,6 @@ bool pmp_is_range_in_tlb(CPURISCVState *env, hwaddr tlb_sa,
                          target_ulong *tlb_size);
 void pmp_update_rule_addr(CPURISCVState *env, uint32_t pmp_index);
 void pmp_update_rule_nums(CPURISCVState *env);
+uint32_t pmp_get_num_rules(CPURISCVState *env);
 
 #endif