Kernel/aarch64: Set Access Permission EL0 bit for userspace mappings

This bit was not set, which was causing Permission Faults when executing
in userspace.

Kernel/Arch/aarch64/PageDirectory.h

@@ -40,10 +40,8 @@ constexpr u32 INNER_SHAREABLE = (3 << 8);
 constexpr u32 NORMAL_MEMORY = (0 << 2);
 constexpr u32 DEVICE_MEMORY = (1 << 2);
 
-constexpr u32 ACCESS_PERMISSION_READWRITE = (0b00 << 6);
-constexpr u32 ACCESS_PERMISSION_READWRITE_EL0 = (0b01 << 6);
-constexpr u32 ACCESS_PERMISSION_READONLY = (0b10 << 6);
-constexpr u32 ACCESS_PERMISSION_READONLY_EL0 = (0b11 << 6);
+constexpr u32 ACCESS_PERMISSION_EL0 = (1 << 6);
+constexpr u32 ACCESS_PERMISSION_READONLY = (1 << 7);
 
 // Figure D5-15 of Arm Architecture Reference Manual Armv8 - page D5-2588
 class PageDirectoryEntry {
@@ -127,8 +125,8 @@ public:
     bool is_present() const { return (raw() & Present) == Present; }
     void set_present(bool b) { set_bit(Present, b); }
 
-    bool is_user_allowed() const { TODO_AARCH64(); }
-    void set_user_allowed(bool) { }
+    bool is_user_allowed() const { return (raw() & ACCESS_PERMISSION_EL0) == ACCESS_PERMISSION_EL0; }
+    void set_user_allowed(bool b) { set_bit(ACCESS_PERMISSION_EL0, b); }
 
     bool is_writable() const { return !((raw() & ACCESS_PERMISSION_READONLY) == ACCESS_PERMISSION_READONLY); }
     void set_writable(bool b) { set_bit(ACCESS_PERMISSION_READONLY, !b); }