LibC: Implement guard page for pthread

Author: NoobZang

Kernel/API/Syscall.h

@@ -361,7 +361,6 @@ struct SC_getkeymap_params {
 struct SC_create_thread_params {
     unsigned int detach_state = 0; // JOINABLE or DETACHED
     int schedule_priority = 30;    // THREAD_PRIORITY_NORMAL
-    // FIXME: Implement guard pages in create_thread (unreadable pages at "overflow" end of stack)
     // "If an implementation rounds up the value of guardsize to a multiple of {PAGESIZE},
     // a call to pthread_attr_getguardsize() specifying attr shall store in the guardsize
     // parameter the guard size specified by the previous pthread_attr_setguardsize() function call"

Kernel/Syscalls/thread.cpp

@@ -41,8 +41,6 @@ ErrorOr<FlatPtr> Process::sys$create_thread(void* (*entry)(void*), Userspace<Sys
 
     bool is_thread_joinable = (0 == detach_state);
 
-    // FIXME: Do something with guard pages?
-
     auto thread = TRY(Thread::create(*this));
 
     // We know this thread is not the main_thread,

Userland/Libraries/LibC/pthread.cpp

@@ -136,9 +136,20 @@ int pthread_create(pthread_t* thread, pthread_attr_t const* attributes, void* (*
         if (0 != (used_attributes->stack_size % required_stack_alignment))
             used_attributes->stack_size += required_stack_alignment - (used_attributes->stack_size % required_stack_alignment);
 
-        used_attributes->stack_location = mmap_with_name(nullptr, used_attributes->stack_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, 0, 0, "Thread stack");
-        if (!used_attributes->stack_location)
+        // According to POSIX, if the stack address attribute has been set in attr,
+        // then the guard size attribute is ignored: it is the application's responsibility
+        // to handle stack overflow.
+        size_t total_size = used_attributes->stack_size + used_attributes->guard_page_size;
+        void* memory_location = mmap_with_name(nullptr, total_size, used_attributes->guard_page_size == 0 ? PROT_READ | PROT_WRITE : PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, 0, 0, "Thread stack");
+        if (!memory_location)
             return -1;
+        if (used_attributes->guard_page_size > 0) {
+            if (mprotect((void*)((FlatPtr)memory_location + used_attributes->guard_page_size), used_attributes->stack_size, PROT_READ | PROT_WRITE) < 0) {
+                munmap(memory_location, total_size);
+                return -1;
+            }
+        }
+        used_attributes->stack_location = (void*)((FlatPtr)memory_location + used_attributes->guard_page_size);
     }
 
     dbgln_if(PTHREAD_DEBUG, "pthread_create: Creating thread with attributes at {}, detach state {}, priority {}, guard page size {}, stack size {}, stack location {}",