Kernel: Add copy_from_user() and copy_from_user_typed()

kernel/src/memory/MemoryManager.cpp

@@ -438,7 +438,6 @@ namespace MemoryManager
         // Userspace pointer not aligned on page boundary
         if (user_ptr != user_page)
         {
-            // FIXME: Validate that this page is writable by the user, not just the kernel.
             if (!validate_user_writable_page(user_page)) return false;
         }
 
@@ -457,6 +456,34 @@ namespace MemoryManager
         return true;
     }
 
+    bool copy_from_user(const void* user, void* kernel, usize size)
+    {
+        uintptr_t user_ptr = (uintptr_t)user;
+        uintptr_t user_page = align_down<ARCH_PAGE_SIZE>(user_ptr);
+
+        char* kernel_ptr = (char*)kernel;
+
+        // Userspace pointer not aligned on page boundary
+        if (user_ptr != user_page)
+        {
+            if (!validate_user_writable_page(user_page)) return false;
+        }
+
+        while (size--)
+        {
+            // Crossed a page boundary, gotta check the page tables again before touching any memory!!
+            if (user_ptr % ARCH_PAGE_SIZE)
+            {
+                if (!validate_user_writable_page(user_ptr)) return false;
+            }
+
+            *kernel_ptr++ = *(char*)user_ptr;
+            user_ptr++;
+        }
+
+        return true;
+    }
+
     usize free()
     {
         return free_mem;

kernel/src/memory/MemoryManager.h

@@ -45,6 +45,13 @@ namespace MemoryManager
         return copy_to_user(user, kernel, sizeof(T));
     }
 
+    bool copy_from_user(const void* user, void* kernel, usize size);
+
+    template <typename T> bool copy_from_user_typed(const T* user, T* kernel)
+    {
+        return copy_from_user(user, kernel, sizeof(T));
+    }
+
     Result<void> map_frames_at(u64 virt, u64 phys, usize count, int flags);
 
     Result<u64> alloc_at(u64 virt, usize count, int flags);