feat: implement memory management system calls (brk, mmap, munmap, mprotect)

1 files changed, 172 insertions, 0 deletions

diff --git a/na/kernel/sys_mm.cc b/na/kernel/sys_mm.cc
new file mode 100644
index 0000000..ff03e96
--- /dev/null
+++ b/na/kernel/sys_mm.cc
@@ -0,0 +1,172 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * Memory Management System Calls
+ *
+ * Implements: brk, mmap (anonymous only), munmap, mprotect.
+ *
+ * Reference: docs/specs/syscall.md §7.2
+ */
+
+#include <lume/types.h>
+#include <lume/task.h>
+#include <lume/vmm.h>
+#include <lume/errno.h>
+#include <lume/mman.h>
+#include <lume/config.h>
+
+
+/* Page alignment helpers */
+static inline uint64 page_align_up(uint64 x)
+{
+    return (x + kPageSize - 1) & ~(kPageSize - 1);
+}
+
+static inline uint64 page_align_down(uint64 x)
+{
+    return x & ~(kPageSize - 1);
+}
+
+/* ======================================================================
+ * sys_brk
+ * ====================================================================== */
+
+int64 sys_brk(uint64 new_brk, uint64, uint64, uint64, uint64, uint64)
+{
+    VmSpace* mm = current_task()->mm;
+    if (!mm)
+        return -ENOMEM; /* kernel threads have no user address space */
+
+    if (new_brk == 0) {
+        return static_cast<int64>(mm->brk_end);
+    }
+
+    if (mm->brk_start == 0) {
+        uint64 init_brk = page_align_up(new_brk);
+        mm->brk_start = init_brk;
+        mm->brk_end = init_brk;
+    }
+
+    if (new_brk < mm->brk_start) {
+        return -EINVAL;
+    }
+
+    uint64 new_end = page_align_up(new_brk);
+    if (new_end > mm->brk_end) {
+        uint64 grow = new_end - mm->brk_end;
+        int ret = vmm_map_user(mm, mm->brk_end, grow, VM_READ | VM_WRITE);
+        if (ret < 0) {
+            return ret;
+        }
+    } else if (new_end < mm->brk_end) {
+        uint64 shrink = mm->brk_end - new_end;
+        int ret = vmm_unmap_user(mm, new_end, shrink);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    mm->brk_end = new_end;
+    return static_cast<int64>(new_brk);
+}
+
+/* ======================================================================
+ * sys_mmap
+ * ====================================================================== */
+
+int64 sys_mmap(uint64 addr, uint64 length, uint64 prot,
+               uint64 flags, uint64 fd, uint64 offset)
+{
+    if (length == 0) return -EINVAL;
+    length = page_align_up(length);
+    if (offset % kPageSize != 0) return -EINVAL;
+
+    if ((flags & MAP_PRIVATE) && (flags & MAP_SHARED)) return -EINVAL;
+    if (!(flags & MAP_PRIVATE) && !(flags & MAP_SHARED)) return -EINVAL;
+
+    VmSpace* mm = current_task()->mm;
+    if (!mm) return -ENOMEM;
+
+    /* Phase 2: only anonymous private mappings */
+    if (!(flags & MAP_ANONYMOUS))
+        return -ENOSYS; /* File-backed mmap is Phase 3 */
+    if (flags & MAP_SHARED)
+        return -ENOSYS; /* Shared mappings are Phase 3 */
+
+    (void)fd;
+
+    /* Convert POSIX prot → MI permission flags */
+    uint64 vm_perm = 0;
+    if (prot & PROT_READ)  vm_perm |= VM_READ;
+    if (prot & PROT_WRITE) vm_perm |= VM_WRITE;
+    if (prot & PROT_EXEC)  vm_perm |= VM_EXEC;
+    vm_perm |= VM_USER;
+
+    uint64 va = addr;
+    if (flags & MAP_FIXED) {
+        if (va % kPageSize != 0) return -EINVAL;
+    } else if (va != 0) {
+        va = page_align_down(va);
+    }
+
+    if (va == 0) {
+        va = mm_find_free_va(mm, length, kPageSize);
+        if (!va) return -ENOMEM;
+    }
+
+    if (flags & MAP_FIXED) {
+        int ret = vmm_unmap_user(mm, va, length);
+        if (ret < 0) return ret;
+    }
+
+    int ret = vmm_map_user(mm, va, length, vm_perm);
+    if (ret < 0 && !(flags & MAP_FIXED) && addr != 0) {
+        uint64 fallback = mm_find_free_va(mm, length, kPageSize);
+        if (!fallback) return ret;
+        ret = vmm_map_user(mm, fallback, length, vm_perm);
+        if (ret < 0) return ret;
+        va = fallback;
+    } else if (ret < 0) {
+        return ret;
+    }
+
+    return static_cast<int64>(va);
+}
+
+/* ======================================================================
+ * sys_munmap
+ * ====================================================================== */
+
+int64 sys_munmap(uint64 addr, uint64 length, uint64, uint64, uint64, uint64)
+{
+    if (length == 0) return -EINVAL;
+    if (addr % kPageSize != 0) return -EINVAL;
+    length = page_align_up(length);
+
+    VmSpace* mm = current_task()->mm;
+    if (!mm) return -EINVAL;
+
+    return vmm_unmap_user(mm, addr, length);
+}
+
+/* ======================================================================
+ * sys_mprotect — Phase 2 stub
+ * ====================================================================== */
+
+int64 sys_mprotect(uint64 addr, uint64 len, uint64 prot,
+                   uint64, uint64, uint64)
+{
+    if (len == 0) return -EINVAL;
+    if (addr % kPageSize != 0) return -EINVAL;
+
+    VmSpace* mm = current_task()->mm;
+    if (!mm) return -ENOMEM;
+
+    uint64 vm_perm = 0;
+    if (prot & PROT_READ)  vm_perm |= VM_READ;
+    if (prot & PROT_WRITE) vm_perm |= VM_WRITE;
+    if (prot & PROT_EXEC)  vm_perm |= VM_EXEC;
+
+    return vmm_protect_user(mm, addr, len, vm_perm);
+}