kernel: Make the stack and loaded program code regions persistent

This way, they can't be modified by mmap() or munmap().

kernel/src/memory/UserVM.cpp

@@ -91,7 +91,7 @@ Result<u64> UserVM::alloc_region(usize count, bool persistent)
     return err(ENOMEM);
 }
 
-Result<bool> UserVM::set_region(u64 address, usize count, bool used)
+Result<bool> UserVM::set_region(u64 address, usize count, bool used, bool persistent)
 {
     if (address >= VM_END) return err(EINVAL);
 
@@ -112,6 +112,7 @@ Result<bool> UserVM::set_region(u64 address, usize count, bool used)
         if (region->start >= address && region->end <= end)
         {
             region->used = used;
+            region->persistent = persistent;
             if (region->start == address && region->end == end)
             {
                 try_merge_region_with_neighbors(region);
@@ -125,6 +126,7 @@ Result<bool> UserVM::set_region(u64 address, usize count, bool used)
             auto* middle_region = TRY(split_region(region, address));
             TRY(split_region(middle_region, end));
             middle_region->used = used;
+            middle_region->persistent = persistent;
             return true;
         }
 
@@ -133,6 +135,7 @@ Result<bool> UserVM::set_region(u64 address, usize count, bool used)
             bool finished = region->end == end;
             auto* split = TRY(split_region(region, address));
             split->used = used;
+            split->persistent = persistent;
             try_merge_region_with_neighbors(split);
             if (!finished) continue;
             return true;
@@ -142,6 +145,7 @@ Result<bool> UserVM::set_region(u64 address, usize count, bool used)
         {
             TRY(split_region(region, end));
             region->used = used;
+            region->persistent = persistent;
             try_merge_region_with_neighbors(region);
             return true;
         }

kernel/src/memory/UserVM.h

@@ -21,14 +21,14 @@ class UserVM
 
     Result<u64> alloc_region(usize count, bool persistent = false);
 
-    Result<bool> test_and_alloc_region(u64 address, usize count)
+    Result<bool> test_and_alloc_region(u64 address, usize count, bool persistent = false)
     {
-        return set_region(address, count, true);
+        return set_region(address, count, true, persistent);
     }
 
     Result<bool> free_region(u64 address, usize count)
     {
-        return set_region(address, count, false);
+        return set_region(address, count, false, false);
     }
 
     static Result<OwnedPtr<UserVM>> try_create();
@@ -36,7 +36,7 @@ class UserVM
     Result<OwnedPtr<UserVM>> clone();
 
   private:
-    Result<bool> set_region(u64 address, usize count, bool used);
+    Result<bool> set_region(u64 address, usize count, bool used, bool persistent);
     Result<void> create_default_region();
     Result<void> create_null_region();
     void try_merge_region_with_neighbors(VMRegion* region);

kernel/src/thread/ELF.cpp

@@ -102,9 +102,8 @@ namespace ELFLoader
                 if (can_write_segment(program_header.p_flags)) flags |= MMU::ReadWrite;
                 if (can_execute_segment(program_header.p_flags)) flags &= ~MMU::NoExecute;
 
-                // FIXME: Set this memory range to persistent so that munmap() cannot remove it.
                 if (!TRY(vm->test_and_alloc_region(
-                        base_vaddr, get_blocks_from_size(program_header.p_memsz + vaddr_diff, ARCH_PAGE_SIZE))))
+                        base_vaddr, get_blocks_from_size(program_header.p_memsz + vaddr_diff, ARCH_PAGE_SIZE), true)))
                     return err(ENOMEM);
 
                 // Allocate physical memory for the segment

kernel/src/thread/ThreadImage.cpp

@@ -11,8 +11,7 @@ static Result<void> create_stacks(Stack& user_stack, Stack& kernel_stack, UserVM
 {
     const u64 THREAD_STACK_BASE = 0x10000;
 
-    // FIXME: Set this memory range to persistent so that munmap() cannot remove it.
-    if (!TRY(vm->test_and_alloc_region(THREAD_STACK_BASE, DEFAULT_USER_STACK_PAGES))) return err(ENOMEM);
+    if (!TRY(vm->test_and_alloc_region(THREAD_STACK_BASE, DEFAULT_USER_STACK_PAGES, true))) return err(ENOMEM);
 
     TRY(MemoryManager::alloc_at_zeroed(THREAD_STACK_BASE, DEFAULT_USER_STACK_PAGES,
                                        MMU::ReadWrite | MMU::NoExecute | MMU::User));