Only check user pages rather than all bytes in-between, for known-size pointers

src/threads/synch.c

@@ -212,7 +212,6 @@ donate_priority (struct thread *donee) {
   ASSERT (intr_get_level () == INTR_OFF);
 
   struct thread *donor = thread_current ();
-  list_remove (&donor->donor_elem);
   list_push_back (&donee->donors_list, &donor->donor_elem);
   
   while (donee != NULL)
@@ -261,7 +260,6 @@ lock_acquire (struct lock *lock)
   ASSERT (!lock_held_by_current_thread (lock));
 
   struct thread *t = thread_current ();
-  ASSERT (t->waiting_lock == NULL);
 
   enum intr_level old_level = intr_disable ();
   if (lock->holder != NULL)
@@ -343,6 +341,7 @@ lock_release (struct lock *lock)
      released, transfer the remaining orphaned donors to its donor list. */
   if (max_donor != NULL)
     {
+      list_remove (&max_donor->donor_elem);
       while (!list_empty (&orphan_list))
         list_push_back (&max_donor->donors_list, list_pop_front (&orphan_list));
     }

src/threads/thread.c

@@ -373,9 +373,7 @@ thread_exit (void)
      and schedule another process.  That process will destroy us
      when it calls thread_schedule_tail(). */
   intr_disable ();
-  struct thread *t = thread_current ();
+  list_remove (&thread_current()->allelem);
-  list_remove (&t->allelem);
-  list_remove (&t->donor_elem);
   thread_current ()->status = THREAD_DYING;
   schedule ();
   NOT_REACHED ();
@@ -681,7 +679,6 @@ init_thread (struct thread *t, const char *name, int nice, int priority,
   t->base_priority
       = thread_mlfqs ? calculate_bsd_priority (recent_cpu, nice) : priority;
   list_init (&t->donors_list);
-  list_push_back (&t->donors_list, &t->donor_elem);
   t->waiting_lock = NULL;
 
   t->nice = nice;

src/userprog/exception.c

@@ -145,6 +145,14 @@ page_fault (struct intr_frame *f)
   write = (f->error_code & PF_W) != 0;
   user = (f->error_code & PF_U) != 0;
 
+  /* Kernel page fault is further handled by the kernel itself. */
+  if (!user)
+    {
+      f->eip = (void *)f->eax;
+      f->eax = 0xffffffff;
+      return;
+    }
+
   /* To implement virtual memory, delete the rest of the function
      body, and replace it with code that brings in the page to
      which fault_addr refers. */

src/userprog/process.c

@@ -8,7 +8,6 @@
 #include <string.h>
 #include "userprog/gdt.h"
 #include "userprog/pagedir.h"
-#include "userprog/syscall.h"
 #include "userprog/tss.h"
 #include "filesys/directory.h"
 #include "filesys/file.h"
@@ -82,14 +81,8 @@ process_execute (const char *cmd)
      of the process. */
   char *file_name = strtok_r (cmd_copy, " ", &data->cmd_saveptr);
 
-  /* NOTE: Currently, the file being executed is closed in load () and then
-          reopened here. Because load is an exported public function, this
-          might be necessary. */
-  lock_acquire (&filesys_lock);
 /* Validates that the current file to be executed is a valid file */
-  bool valid_file = filesys_open (file_name) != NULL;
+if (filesys_open (file_name) == NULL)
-  lock_release (&filesys_lock);
-  if (!valid_file)
     return TID_ERROR;
 
   /* Create a new thread to execute the command, by initializing
@@ -127,15 +120,6 @@ start_process (void *proc_start_data)
   if_.gs = if_.fs = if_.es = if_.ds = if_.ss = SEL_UDSEG;
   if_.cs = SEL_UCSEG;
   if_.eflags = FLAG_IF | FLAG_MBS;
-  
-  lock_acquire (&filesys_lock);
-  
-  /* Prevent writing to the file being executed. */
-  struct file *exec_file = filesys_open (data->file_name);
-  thread_current ()->exec_file = exec_file;
-  file_deny_write (exec_file);
-  lock_release (&filesys_lock);
-
   success = load (data->file_name, &if_.eip, &if_.esp);
 
   /* If load failed, quit. */
@@ -157,6 +141,13 @@ start_process (void *proc_start_data)
       goto fail;
     }
 
+  /* NOTE: Currently, the file being executed is closed in load () and then 
+           reopened here. Because load is an exported public function, this
+           might be necessary. */
+  struct file *exec_file = filesys_open (data->file_name);
+  thread_current ()->exec_file = exec_file;
+  file_deny_write (exec_file);
+
   /* Start the user process by simulating a return from an
      interrupt, implemented by intr_exit (in
      threads/intr-stubs.S).  Because intr_exit takes all of its
@@ -325,13 +316,7 @@ process_exit (void)
   uint32_t *pd;
 
   printf ("%s: exit(%d)\n", cur->name, cur->exit_status);
-  if (cur->exec_file != NULL)
-    {
-      lock_acquire (&filesys_lock);
-      file_allow_write (cur->exec_file);
   file_close (cur->exec_file);
-      lock_release (&filesys_lock);
-    }
 
   /* Update process result. */
   if (cur->result != NULL)
@@ -491,7 +476,6 @@ load (const char *file_name, void (**eip) (void), void **esp)
   off_t file_ofs;
   bool success = false;
   int i;
-  lock_acquire (&filesys_lock);
 
   /* Allocate and activate page directory. */
   t->pagedir = pagedir_create ();
@@ -591,7 +575,6 @@ load (const char *file_name, void (**eip) (void), void **esp)
  done:
   /* We arrive here whether the load is successful or not. */
   file_close (file);
-  lock_release (&filesys_lock);
   return success;
 }
 

src/userprog/syscall.c

@@ -11,8 +11,12 @@
 #include "userprog/process.h"
 #include "userprog/pagedir.h"
 #include <stdio.h>
+#include <stdbool.h>
 #include <syscall-nr.h>
 
+#define MAX_SYSCALL_ARGS 3
+
+static struct lock filesys_lock;
 static unsigned fd_counter = MIN_USER_FD;
 
 struct open_file
@@ -45,7 +49,11 @@ static unsigned syscall_tell (int fd);
 static void syscall_close (int fd);
 
 static struct open_file *fd_get_file (int fd);
-static void *validate_user_pointer (const void *ptr, size_t size);
+static void validate_user_pointer (const void *ptr, size_t size,
+                                   bool check_write);
+static void validate_user_string (const char *str, bool check_write);
+static int get_user (const uint8_t *);
+static bool put_user (uint8_t *, uint8_t);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 typedef struct
@@ -95,8 +103,8 @@ static void
 syscall_handler (struct intr_frame *f)
 {
   /* First, read the system call number from the stack. */
-  validate_user_pointer (f->esp, 1);
+  validate_user_pointer (f->esp, sizeof (uintptr_t), false);
-  unsigned syscall_number = *(int *) f->esp;
+  uintptr_t syscall_number = *(int *)f->esp;
 
   /* Ensures the number corresponds to a system call that can be handled. */
   if (syscall_number >= LOOKUP_SIZE)
@@ -106,9 +114,9 @@ syscall_handler (struct intr_frame *f)
 
   /* Next, read and copy the arguments from the stack pointer. */
   validate_user_pointer (f->esp + sizeof (uintptr_t),
-                         syscall.arity * sizeof (uintptr_t));
+                         syscall.arity * sizeof (uintptr_t), false);
-  uintptr_t args[3] = {0};
+  uintptr_t args[MAX_SYSCALL_ARGS] = { 0 };
-  for (int i=0; i < syscall.arity; i++)
+  for (int i = 0; i < syscall.arity && i < MAX_SYSCALL_ARGS; i++)
     args[i] = *(uintptr_t *)(f->esp + sizeof (uintptr_t) * (i + 1));
 
   /* Call the function that handles this system call with the arguments. When
@@ -140,9 +148,11 @@ syscall_exit (int status)
 static pid_t
 syscall_exec (const char *cmd_line)
 {
-  validate_user_pointer (cmd_line, 1);
+  validate_user_string (cmd_line, false);
 
+  lock_acquire (&filesys_lock);
   pid_t pid = process_execute(cmd_line);
+  lock_release (&filesys_lock);
 
   return pid;
 }
@@ -161,7 +171,7 @@ syscall_wait (pid_t pid)
 static bool
 syscall_create (const char *file UNUSED, unsigned initial_size UNUSED)
 {
-  validate_user_pointer (file, 1);
+  validate_user_string (file, false);
 
   lock_acquire (&filesys_lock);
   bool status = filesys_create (file, initial_size);
@@ -176,7 +186,7 @@ syscall_create (const char *file UNUSED, unsigned initial_size UNUSED)
 static bool
 syscall_remove (const char *file)
 {
-  validate_user_pointer (file, 1);
+  validate_user_string (file, false);
 
   lock_acquire (&filesys_lock);
   bool status = filesys_remove (file);
@@ -192,7 +202,7 @@ syscall_remove (const char *file)
 static int
 syscall_open (const char *file)
 {
-  validate_user_pointer (file, 1);
+  validate_user_string (file, false);
 
   lock_acquire (&filesys_lock);
   struct file *ptr = filesys_open (file);
@@ -247,7 +257,7 @@ syscall_read (int fd, void *buffer, unsigned size)
   if (fd < 0 || fd == STDOUT_FILENO)
     return -1;
 
-  validate_user_pointer (buffer, size);
+  validate_user_pointer (buffer, size, true);
 
   if (fd == STDIN_FILENO)
     {
@@ -284,7 +294,7 @@ syscall_write (int fd, const void *buffer, unsigned size)
   if (fd <= 0)
     return 0;
 
-  validate_user_pointer (buffer, size);
+  validate_user_pointer (buffer, size, false);
 
   if (fd == STDOUT_FILENO)
     {
@@ -398,17 +408,75 @@ fd_get_file (int fd)
 }
 
 /* Validates if a block of memory starting at PTR and of size SIZE bytes is
-   fully contained within user virtual memory. Kills the thread (by calling
+   fully contained within valid user virtual memory. thread_exit () if the
-   thread_exit) if the memory is invalid. Otherwise, returns the PTR given.
+   memory is invalid.
    If the size is 0, the function does no checks and returns PTR. */
-static void *
+static void
-validate_user_pointer (const void *ptr, size_t size)
+validate_user_pointer (const void *ptr, size_t size, bool check_write)
 {
-  if (size > 0 && (ptr == NULL ||
+  if (size == 0)
-                   !is_user_vaddr (ptr) ||
+    return;
-                   !is_user_vaddr (ptr + size - 1) ||
+  /* ptr < ptr + size - 1, so sufficient to check that (ptr + size -1) is a
-                   pagedir_get_page (thread_current()->pagedir, ptr) == NULL))
+     valid user virtual memory address. */
+  void *last = ptr + size - 1;
+  if (!is_user_vaddr (last))
     thread_exit ();
-
+  ptr = pg_round_down (ptr);
-  return (void *) ptr;
+  while (ptr <= last)
+    {
+      int result;
+      /* Check read access to pointer. */
+      if ((result = get_user (ptr)) == -1)
+        thread_exit ();
+      /* Check write access to pointer (if required). */
+      if (check_write && !put_user (ptr, result))
+        thread_exit ();
+      ptr += PGSIZE;
+    }
+}
+
+/* Validates of a C-string starting at ptr is fully contained within valid
+   user virtual memory. thread_exit () if the memory is invalid. */
+static void
+validate_user_string (const char *ptr, bool check_write)
+{
+  while (true)
+    {
+      if (!is_user_vaddr (ptr))
+        thread_exit ();
+      int result;
+      if ((result = get_user ((const uint8_t *)ptr)) == -1)
+        thread_exit ();
+      if (check_write && !put_user ((uint8_t *)ptr, result))
+        thread_exit ();
+      if (*ptr == '\0')
+        return;
+      ptr++;
+    }
+}
+
+/* PROVIDED BY SPEC.
+   Reads a byte at user virtual address UADDR.
+   UADDR must be below PHYS_BASE.
+   Returns the byte value if successful, -1 if a segfault occurred. */
+static int
+get_user (const uint8_t *uaddr)
+{
+  int result;
+  asm ("movl $1f, %0; movzbl %1, %0; 1:" : "=&a"(result) : "m"(*uaddr));
+  return result;
+}
+
+/* PROVIDED BY SPEC.
+   Writes BYTE to user address UDST.
+   UDST must be below PHYS_BASE.
+   Returns true if successful, false if a segfault occurred. */
+static bool
+put_user (uint8_t *udst, uint8_t byte)
+{
+  int error_code;
+  asm ("movl $1f, %0; movb %b2, %1; 1:"
+       : "=&a"(error_code), "=m"(*udst)
+       : "q"(byte));
+  return error_code != -1;
 }

src/userprog/syscall.h

@@ -2,14 +2,11 @@
 #define USERPROG_SYSCALL_H
 
 #include <hash.h>
-#include "threads/synch.h"
 
 #define MIN_USER_FD 2
 
 typedef int pid_t;
 
-struct lock filesys_lock;
-
 void syscall_init (void);
 
 unsigned fd_hash (const struct hash_elem *element, void *aux);