Kernel + LibPthread: Use Userspace<T> in the create_thread syscall

Kernel/API/Syscall.h

@@ -355,7 +355,7 @@ struct SC_create_thread_params {
     unsigned int m_guard_page_size = 0;          // Rounded up to PAGE_SIZE
     unsigned int m_reported_guard_page_size = 0; // The lie we tell callers
     unsigned int m_stack_size = 4 * MB;          // Default PTHREAD_STACK_MIN
-    void* m_stack_location = nullptr;            // nullptr means any, o.w. process virtual address
+    Userspace<void*> m_stack_location;           // nullptr means any, o.w. process virtual address
 };
 
 struct SC_realpath_params {

Kernel/Process.h

@@ -296,7 +296,7 @@ public:
     int sys$getpeername(const Syscall::SC_getpeername_params*);
     int sys$sched_setparam(pid_t pid, Userspace<const struct sched_param*>);
     int sys$sched_getparam(pid_t pid, Userspace<struct sched_param*>);
-    int sys$create_thread(void* (*)(void*), const Syscall::SC_create_thread_params*);
+    int sys$create_thread(void* (*)(void*), Userspace<const Syscall::SC_create_thread_params*>);
     void sys$exit_thread(void*);
     int sys$join_thread(int tid, void** exit_value);
     int sys$detach_thread(int tid);

Kernel/Syscalls/thread.cpp

@@ -33,7 +33,7 @@
 
 namespace Kernel {
 
-int Process::sys$create_thread(void* (*entry)(void*), const Syscall::SC_create_thread_params* user_params)
+int Process::sys$create_thread(void* (*entry)(void*), Userspace<const Syscall::SC_create_thread_params*> user_params)
 {
     REQUIRE_PROMISE(thread);
     if (!validate_read((const void*)entry, sizeof(void*)))
@@ -45,13 +45,13 @@ int Process::sys$create_thread(void* (*entry)(void*), const Syscall::SC_create_t
 
     unsigned detach_state = params.m_detach_state;
     int schedule_priority = params.m_schedule_priority;
-    void* stack_location = params.m_stack_location;
+    Userspace<void*> stack_location = params.m_stack_location;
     unsigned stack_size = params.m_stack_size;
 
     if (!validate_write(stack_location, stack_size))
         return -EFAULT;
 
-    u32 user_stack_address = reinterpret_cast<u32>(stack_location) + stack_size;
+    u32 user_stack_address = reinterpret_cast<u32>(stack_location.ptr()) + stack_size;
 
     if (!MM.validate_user_stack(*this, VirtualAddress(user_stack_address - 4)))
         return -EFAULT;

Libraries/LibPthread/pthread.cpp

@@ -383,7 +383,7 @@ int pthread_attr_getstack(const pthread_attr_t* attributes, void** p_stack_ptr,
     if (!attributes_impl || !p_stack_ptr || !p_stack_size)
         return EINVAL;
 
-    *p_stack_ptr = attributes_impl->m_stack_location;
+    *p_stack_ptr = attributes_impl->m_stack_location.ptr();
     *p_stack_size = attributes_impl->m_stack_size;
 
     return 0;