handle non-canonical addresses in vmm

kernel/src/kmain.c

@@ -51,27 +51,6 @@ __noreturn void _start(void) {
 		printk("%d: %lu\n", i, get_random_number());
 	}
 
-	// test VMM
-	{
-		void* vaddr;
-		int ret = vmm_alloc(&vaddr, 2, 0);
-		if (ret != SUCCESS) {
-			panic(NULL, "vmm_alloc returned %d", ret);
-		}
-		{
-			uint64_t* pml4 = pag_get_pml4();
-			uint64_t* pte = pag_get_pte(pml4, vaddr);
-			if (!IS_ERR(pte) && (*pte & PTE_FLAG_PRESENT)) {
-				printk("page allocated\n");
-			} else {
-				printk("page not allocated\n");
-			}
-		}
-		memset(vaddr, 69, 2 * PAGE_SIZE);
-		*(char*)((vaddr + (2 * PAGE_SIZE)) - 1) = 0;
-		printk("read back:\n%s\n", (char*)vaddr);
-	}
-
 	// The most important function in the world.
 	splash();
 

kernel/src/vmm.c

@@ -31,6 +31,18 @@ int vmm_alloc(void** vaddr, uint64_t count, uint64_t flags) {
 					*vaddr = (void*)((uint64_t)(*vaddr) |
 							 CANONICAL_MASK_KERNEL);
 				}
+			} else {
+				if (flags & PTE_FLAG_USER) {
+					if ((void*)((uint64_t)(*vaddr) &
+						    CANONICAL_MASK_KERNEL)) {
+						return -EINVAL;
+					}
+				} else {
+					if (!((void*)((uint64_t)(*vaddr) &
+						      CANONICAL_MASK_KERNEL))) {
+						return -EINVAL;
+					}
+				}
 			}
 			for (uint64_t i = 0; i < count; i++) {
 				uint64_t* pte =