target/riscv: pmp: don't allow RLB to bypass rule privileges

When Smepmp is supported, mseccfg.RLB allows bypassing locks when writing CSRs
but should not affect interpretation of actual PMP rules.

This is not the case with the current implementation where pmp_hart_has_privs
calls pmp_is_locked which implements mseccfg.RLB bypass.

This commit implements the correct behavior by removing mseccfg.RLB bypass from
pmp_is_locked.

RLB bypass when writing CSRs is implemented by adding a new pmp_is_readonly
function that calls pmp_is_locked and check mseccfg.RLB. pmp_write_cfg and
pmpaddr_csr_write are changed to use this new function.

Signed-off-by: Loïc Lefort <loic@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: LIU Zhiwei  <zhiwei_liu@linux.alibaba.com>
Message-ID: <20250313193011.720075-2-loic@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Cc: qemu-stable@nongnu.org

diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index c13a117e3f9fd9fa2f36f2e6b46a737f4036e73f..d8e2949aafe96a801c5d918e66bc96338980b633 100644 (file)
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -46,11 +46,6 @@ static inline uint8_t pmp_get_a_field(uint8_t cfg)
  */
 static inline int pmp_is_locked(CPURISCVState *env, uint32_t pmp_index)
 {
-    /* mseccfg.RLB is set */
-    if (MSECCFG_RLB_ISSET(env)) {
-        return 0;
-    }
-
     if (env->pmp_state.pmp[pmp_index].cfg_reg & PMP_LOCK) {
         return 1;
     }
@@ -63,6 +58,15 @@ static inline int pmp_is_locked(CPURISCVState *env, uint32_t pmp_index)
     return 0;
 }
 
+/*
+ * Check whether a PMP is locked for writing or not.
+ * (i.e. has LOCK flag and mseccfg.RLB is unset)
+ */
+static int pmp_is_readonly(CPURISCVState *env, uint32_t pmp_index)
+{
+    return pmp_is_locked(env, pmp_index) && !MSECCFG_RLB_ISSET(env);
+}
+
 /*
  * Count the number of active rules.
  */
@@ -91,39 +95,38 @@ static inline uint8_t pmp_read_cfg(CPURISCVState *env, uint32_t pmp_index)
 static bool pmp_write_cfg(CPURISCVState *env, uint32_t pmp_index, uint8_t val)
 {
     if (pmp_index < MAX_RISCV_PMPS) {
-        bool locked = true;
+        bool readonly = true;
 
         if (riscv_cpu_cfg(env)->ext_smepmp) {
             /* mseccfg.RLB is set */
             if (MSECCFG_RLB_ISSET(env)) {
-                locked = false;
+                readonly = false;
             }
 
             /* mseccfg.MML is not set */
-            if (!MSECCFG_MML_ISSET(env) && !pmp_is_locked(env, pmp_index)) {
-                locked = false;
+            if (!MSECCFG_MML_ISSET(env) && !pmp_is_readonly(env, pmp_index)) {
+                readonly = false;
             }
 
             /* mseccfg.MML is set */
             if (MSECCFG_MML_ISSET(env)) {
                 /* not adding execute bit */
                 if ((val & PMP_LOCK) != 0 && (val & PMP_EXEC) != PMP_EXEC) {
-                    locked = false;
+                    readonly = false;
                 }
                 /* shared region and not adding X bit */
                 if ((val & PMP_LOCK) != PMP_LOCK &&
                     (val & 0x7) != (PMP_WRITE | PMP_EXEC)) {
-                    locked = false;
+                    readonly = false;
                 }
             }
         } else {
-            if (!pmp_is_locked(env, pmp_index)) {
-                locked = false;
-            }
+            readonly = pmp_is_readonly(env, pmp_index);
         }
 
-        if (locked) {
-            qemu_log_mask(LOG_GUEST_ERROR, "ignoring pmpcfg write - locked\n");
+        if (readonly) {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "ignoring pmpcfg write - read only\n");
         } else if (env->pmp_state.pmp[pmp_index].cfg_reg != val) {
             /* If !mseccfg.MML then ignore writes with encoding RW=01 */
             if ((val & PMP_WRITE) && !(val & PMP_READ) &&
@@ -525,14 +528,14 @@ void pmpaddr_csr_write(CPURISCVState *env, uint32_t addr_index,
             uint8_t pmp_cfg = env->pmp_state.pmp[addr_index + 1].cfg_reg;
             is_next_cfg_tor = PMP_AMATCH_TOR == pmp_get_a_field(pmp_cfg);
 
-            if (pmp_is_locked(env, addr_index + 1) && is_next_cfg_tor) {
+            if (pmp_is_readonly(env, addr_index + 1) && is_next_cfg_tor) {
                 qemu_log_mask(LOG_GUEST_ERROR,
-                              "ignoring pmpaddr write - pmpcfg + 1 locked\n");
+                              "ignoring pmpaddr write - pmpcfg+1 read only\n");
                 return;
             }
         }
 
-        if (!pmp_is_locked(env, addr_index)) {
+        if (!pmp_is_readonly(env, addr_index)) {
             if (env->pmp_state.pmp[addr_index].addr_reg != val) {
                 env->pmp_state.pmp[addr_index].addr_reg = val;
                 pmp_update_rule_addr(env, addr_index);
@@ -543,7 +546,7 @@ void pmpaddr_csr_write(CPURISCVState *env, uint32_t addr_index,
             }
         } else {
             qemu_log_mask(LOG_GUEST_ERROR,
-                          "ignoring pmpaddr write - locked\n");
+                          "ignoring pmpaddr write - read only\n");
         }
     } else {
         qemu_log_mask(LOG_GUEST_ERROR,