Verify memory access permissions in PMP regions

Checks if a memory access falls within a configured region by comparing
the requested address and size against the region boundaries. When a
matching region is found, validates that the region's permissions match
the requested operation type.

Address register read helpers are marked unused as the current
implementation maintains shadow state in memory rather than reading
hardware registers. They remain available for potential future use cases
requiring hardware state verification.

Author: HeatCrab

arch/riscv/pmp.c

@@ -42,8 +42,13 @@ static void write_pmpcfg(uint8_t idx, uint32_t val)
     }
 }
 
-/* Read PMP address register by index (0-15) */
-static uint32_t read_pmpaddr(uint8_t idx)
+/* Read PMP address register by index (0-15)
+ *
+ * Currently unused as the implementation maintains shadow state in memory
+ * rather than reading hardware registers. Provided for API completeness
+ * and potential future use cases requiring hardware state verification.
+ */
+static uint32_t __attribute__((unused)) read_pmpaddr(uint8_t idx)
 {
     switch (idx) {
     case 0: return read_csr_num(CSR_PMPADDR0);
@@ -344,3 +349,41 @@ int32_t pmp_get_region(const pmp_config_t *config, uint8_t region_idx,
 
     return ERR_OK;
 }
+
+int32_t pmp_check_access(const pmp_config_t *config, uint32_t addr,
+                         uint32_t size, uint8_t is_write, uint8_t is_execute)
+{
+    if (!config)
+        return ERR_PMP_INVALID_REGION;
+
+    uint32_t access_end = addr + size;
+
+    /* In TOR mode, check all regions in priority order */
+    for (uint8_t i = 0; i < config->region_count; i++) {
+        const pmp_region_t *region = &config->regions[i];
+
+        /* Skip disabled regions */
+        if (region->addr_start == 0 && region->addr_end == 0)
+            continue;
+
+        /* Check if access falls within this region */
+        if (addr >= region->addr_start && access_end <= region->addr_end) {
+            /* Verify permissions match access type */
+            uint8_t required_perm = 0;
+            if (is_write)
+                required_perm |= PMPCFG_W;
+            if (is_execute)
+                required_perm |= PMPCFG_X;
+            if (!is_write && !is_execute)
+                required_perm = PMPCFG_R;
+
+            if ((region->permissions & required_perm) == required_perm)
+                return 1; /* Access allowed */
+            else
+                return 0; /* Access denied */
+        }
+    }
+
+    /* Access not covered by any region */
+    return 0;
+}