From 30e49846b5f5f93f73e6aa329033eb658bac276a Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 16:21:12 +0000
Subject: [PATCH 01/11] Add more tests for system calls to deal with bad
 buffers given to read and write

---
 src/tests/userprog/Make.tests          | 11 ++++++++---
 src/tests/userprog/Rubric.robustnessCR |  8 ++++++--
 src/tests/userprog/exec-bad-ptr.ck     |  6 +-----
 src/tests/userprog/open-bad-ptr.ck     |  6 +-----
 src/tests/userprog/overflow-stack.c    | 17 +++++++++++++++++
 src/tests/userprog/overflow-stack.ck   | 14 ++++++++++++++
 src/tests/userprog/read-bad-buf.c      | 17 +++++++++++++++++
 src/tests/userprog/read-bad-buf.ck     | 10 ++++++++++
 src/tests/userprog/read-bad-ptr.ck     |  7 +------
 src/tests/userprog/write-bad-buf.c     | 17 +++++++++++++++++
 src/tests/userprog/write-bad-buf.ck    | 10 ++++++++++
 src/tests/userprog/write-bad-ptr.ck    |  7 +------
 12 files changed, 103 insertions(+), 27 deletions(-)
 create mode 100644 src/tests/userprog/overflow-stack.c
 create mode 100644 src/tests/userprog/overflow-stack.ck
 create mode 100644 src/tests/userprog/read-bad-buf.c
 create mode 100644 src/tests/userprog/read-bad-buf.ck
 create mode 100644 src/tests/userprog/write-bad-buf.c
 create mode 100644 src/tests/userprog/write-bad-buf.ck

diff --git a/src/tests/userprog/Make.tests b/src/tests/userprog/Make.tests
index 02c73fe..542ea0b 100644
--- a/src/tests/userprog/Make.tests
+++ b/src/tests/userprog/Make.tests
@@ -9,14 +9,14 @@ sc-bad-arg sc-bad-num sc-boundary sc-boundary-2 halt exit create-normal		\
 create-empty create-null create-bad-ptr create-long create-exists	\
 create-bound open-normal open-missing open-boundary open-empty		\
 open-null open-bad-ptr open-twice close-normal close-twice close-stdin	\
-close-stdout close-bad-fd read-normal read-bad-ptr read-boundary	\
-read-zero read-stdout read-bad-fd write-normal write-bad-ptr		\
+close-stdout close-bad-fd read-normal read-bad-ptr read-bad-buf read-boundary	\
+read-zero read-stdout read-bad-fd write-normal write-bad-ptr write-bad-buf	\
 write-boundary write-zero write-stdin write-bad-fd exec-once exec-arg	\
 exec-large-arg exec-multiple exec-missing exec-over-arg exec-over-args \
 exec-bad-ptr wait-simple wait-twice wait-killed wait-load-kill \
 wait-bad-pid wait-bad-child multi-recurse multi-child-fd rox-simple	\
 rox-child rox-multichild bad-read bad-write bad-read2 bad-write2        \
-bad-jump bad-jump2 bad-maths)
+bad-jump bad-jump2 bad-maths overflow-stack)
 
 tests/userprog_PROGS = $(tests/userprog_TESTS) $(addprefix \
 tests/userprog/,child-simple child-args child-bad child-close child-rox exec-exit)
@@ -36,6 +36,7 @@ tests/userprog/bad-read2_SRC = tests/userprog/bad-read2.c tests/main.c
 tests/userprog/bad-write2_SRC = tests/userprog/bad-write2.c tests/main.c
 tests/userprog/bad-jump2_SRC = tests/userprog/bad-jump2.c tests/main.c
 tests/userprog/bad-maths_SRC = tests/userprog/bad-maths.c tests/main.c
+tests/userprog/overflow-stack_SRC = tests/userprog/overflow-stack.c tests/main.c
 tests/userprog/sc-boundary_SRC = tests/userprog/sc-boundary.c	\
 tests/userprog/boundary.c tests/main.c
 tests/userprog/sc-boundary-2_SRC = tests/userprog/sc-boundary-2.c	\
@@ -66,6 +67,7 @@ tests/userprog/close-stdout_SRC = tests/userprog/close-stdout.c tests/main.c
 tests/userprog/close-bad-fd_SRC = tests/userprog/close-bad-fd.c tests/main.c
 tests/userprog/read-normal_SRC = tests/userprog/read-normal.c tests/main.c
 tests/userprog/read-bad-ptr_SRC = tests/userprog/read-bad-ptr.c tests/main.c
+tests/userprog/read-bad-buf_SRC = tests/userprog/read-bad-buf.c tests/main.c
 tests/userprog/read-boundary_SRC = tests/userprog/read-boundary.c	\
 tests/userprog/boundary.c tests/main.c
 tests/userprog/read-zero_SRC = tests/userprog/read-zero.c tests/main.c
@@ -73,6 +75,7 @@ tests/userprog/read-stdout_SRC = tests/userprog/read-stdout.c tests/main.c
 tests/userprog/read-bad-fd_SRC = tests/userprog/read-bad-fd.c tests/main.c
 tests/userprog/write-normal_SRC = tests/userprog/write-normal.c tests/main.c
 tests/userprog/write-bad-ptr_SRC = tests/userprog/write-bad-ptr.c tests/main.c
+tests/userprog/write-bad-buf_SRC = tests/userprog/write-bad-buf.c tests/main.c
 tests/userprog/write-boundary_SRC = tests/userprog/write-boundary.c	\
 tests/userprog/boundary.c tests/main.c
 tests/userprog/write-zero_SRC = tests/userprog/write-zero.c tests/main.c
@@ -122,10 +125,12 @@ tests/userprog/close-normal_PUTFILES += tests/userprog/sample.txt
 tests/userprog/close-twice_PUTFILES += tests/userprog/sample.txt
 tests/userprog/read-normal_PUTFILES += tests/userprog/sample.txt
 tests/userprog/read-bad-ptr_PUTFILES += tests/userprog/sample.txt
+tests/userprog/read-bad-buf_PUTFILES += tests/userprog/sample.txt
 tests/userprog/read-boundary_PUTFILES += tests/userprog/sample.txt
 tests/userprog/read-zero_PUTFILES += tests/userprog/sample.txt
 tests/userprog/write-normal_PUTFILES += tests/userprog/sample.txt
 tests/userprog/write-bad-ptr_PUTFILES += tests/userprog/sample.txt
+tests/userprog/write-bad-buf_PUTFILES += tests/userprog/sample.txt
 tests/userprog/write-boundary_PUTFILES += tests/userprog/sample.txt
 tests/userprog/write-zero_PUTFILES += tests/userprog/sample.txt
 tests/userprog/multi-child-fd_PUTFILES += tests/userprog/sample.txt
diff --git a/src/tests/userprog/Rubric.robustnessCR b/src/tests/userprog/Rubric.robustnessCR
index 9784817..256caed 100644
--- a/src/tests/userprog/Rubric.robustnessCR
+++ b/src/tests/userprog/Rubric.robustnessCR
@@ -1,5 +1,9 @@
-Full robustness of argument passing code:
-- Test user stack overflow robustness of "exec" system calls.
+Full robustness of argument passing and syscall handling code:
+- Test user stack overflow robustness of "exec" system calls and user code.
 5	exec-over-arg
 5	exec-over-args
+5	overflow-stack
 
+- Test syscall user provided buffer validity checks.
+5	read-bad-buf
+5	write-bad-buf
diff --git a/src/tests/userprog/exec-bad-ptr.ck b/src/tests/userprog/exec-bad-ptr.ck
index 63f5f78..7f2604c 100644
--- a/src/tests/userprog/exec-bad-ptr.ck
+++ b/src/tests/userprog/exec-bad-ptr.ck
@@ -2,11 +2,7 @@
 use strict;
 use warnings;
 use tests::tests;
-check_expected ([<<'EOF', <<'EOF']);
-(exec-bad-ptr) begin
-(exec-bad-ptr) end
-exec-bad-ptr: exit(0)
-EOF
+check_expected ([<<'EOF']);
 (exec-bad-ptr) begin
 exec-bad-ptr: exit(-1)
 EOF
diff --git a/src/tests/userprog/open-bad-ptr.ck b/src/tests/userprog/open-bad-ptr.ck
index 45349e2..fa686d0 100644
--- a/src/tests/userprog/open-bad-ptr.ck
+++ b/src/tests/userprog/open-bad-ptr.ck
@@ -2,11 +2,7 @@
 use strict;
 use warnings;
 use tests::tests;
-check_expected ([<<'EOF', <<'EOF']);
-(open-bad-ptr) begin
-(open-bad-ptr) end
-open-bad-ptr: exit(0)
-EOF
+check_expected ([<<'EOF']);
 (open-bad-ptr) begin
 open-bad-ptr: exit(-1)
 EOF
diff --git a/src/tests/userprog/overflow-stack.c b/src/tests/userprog/overflow-stack.c
new file mode 100644
index 0000000..d7c9c85
--- /dev/null
+++ b/src/tests/userprog/overflow-stack.c
@@ -0,0 +1,17 @@
+/* Attempt to overflow the user stack by allocating a 4kB buffer and writing into it.
+   The process must be terminated with -1 exit code until stack growth has been implemented in Task 3
+*/
+
+#include <string.h>
+#include <syscall.h>
+#include "tests/lib.h"
+#include "tests/main.h"
+
+void
+test_main (void)
+{
+  char stack_obj[4096];
+  memset (stack_obj, 'a', sizeof stack_obj);
+  memset (stack_obj+10, '\0', 1);
+  msg ("buffer: %s", stack_obj);
+}
diff --git a/src/tests/userprog/overflow-stack.ck b/src/tests/userprog/overflow-stack.ck
new file mode 100644
index 0000000..8998230
--- /dev/null
+++ b/src/tests/userprog/overflow-stack.ck
@@ -0,0 +1,14 @@
+# -*- perl -*-
+use strict;
+use warnings;
+use tests::tests;
+check_expected (IGNORE_USER_FAULTS => 1, [<<'EOF',<<'EOF']);
+(overflow-stack) begin
+overflow-stack: exit(-1)
+EOF
+(overflow-stack) begin
+(overflow-stack) buffer: aaaaaaaaaa
+(overflow-stack) end
+overflow-stack: exit(0)
+EOF
+pass;
diff --git a/src/tests/userprog/read-bad-buf.c b/src/tests/userprog/read-bad-buf.c
new file mode 100644
index 0000000..d2dc613
--- /dev/null
+++ b/src/tests/userprog/read-bad-buf.c
@@ -0,0 +1,17 @@
+/* Passes a buffer to the read system call that starts in valid memory, but runs into kernel space.
+   The process must be terminated with -1 exit code.
+*/
+
+#include <syscall.h>
+#include "tests/lib.h"
+#include "tests/main.h"
+
+void
+test_main (void)
+{
+  int handle;
+  CHECK ((handle = open ("sample.txt")) > 1, "open \"sample.txt\"");
+
+  read (handle, (char *) 0xbfffffe0, 100);
+  fail ("should not have survived read()");
+}
diff --git a/src/tests/userprog/read-bad-buf.ck b/src/tests/userprog/read-bad-buf.ck
new file mode 100644
index 0000000..703b633
--- /dev/null
+++ b/src/tests/userprog/read-bad-buf.ck
@@ -0,0 +1,10 @@
+# -*- perl -*-
+use strict;
+use warnings;
+use tests::tests;
+check_expected (IGNORE_KERNEL_FAULTS => 1, [<<'EOF']);
+(read-bad-buf) begin
+(read-bad-buf) open "sample.txt"
+read-bad-buf: exit(-1)
+EOF
+pass;
diff --git a/src/tests/userprog/read-bad-ptr.ck b/src/tests/userprog/read-bad-ptr.ck
index d10accf..abd67f7 100644
--- a/src/tests/userprog/read-bad-ptr.ck
+++ b/src/tests/userprog/read-bad-ptr.ck
@@ -2,12 +2,7 @@
 use strict;
 use warnings;
 use tests::tests;
-check_expected ([<<'EOF', <<'EOF']);
-(read-bad-ptr) begin
-(read-bad-ptr) open "sample.txt"
-(read-bad-ptr) end
-read-bad-ptr: exit(0)
-EOF
+check_expected ([<<'EOF']);
 (read-bad-ptr) begin
 (read-bad-ptr) open "sample.txt"
 read-bad-ptr: exit(-1)
diff --git a/src/tests/userprog/write-bad-buf.c b/src/tests/userprog/write-bad-buf.c
new file mode 100644
index 0000000..589499c
--- /dev/null
+++ b/src/tests/userprog/write-bad-buf.c
@@ -0,0 +1,17 @@
+/* Passes a buffer to the write system call that starts in valid memory, but runs into kernel space.
+   The process must be terminated with -1 exit code.
+*/
+
+#include <syscall.h>
+#include "tests/lib.h"
+#include "tests/main.h"
+
+void
+test_main (void)
+{
+  int handle;
+  CHECK ((handle = open ("sample.txt")) > 1, "open \"sample.txt\"");
+
+  write (handle, (char *) 0xbffffff0, 32);
+  fail ("should have exited with -1");
+}
diff --git a/src/tests/userprog/write-bad-buf.ck b/src/tests/userprog/write-bad-buf.ck
new file mode 100644
index 0000000..b0678cb
--- /dev/null
+++ b/src/tests/userprog/write-bad-buf.ck
@@ -0,0 +1,10 @@
+# -*- perl -*-
+use strict;
+use warnings;
+use tests::tests;
+check_expected (IGNORE_KERNEL_FAULTS => 1, [<<'EOF']);
+(write-bad-buf) begin
+(write-bad-buf) open "sample.txt"
+write-bad-buf: exit(-1)
+EOF
+pass;
diff --git a/src/tests/userprog/write-bad-ptr.ck b/src/tests/userprog/write-bad-ptr.ck
index ad9f399..3014879 100644
--- a/src/tests/userprog/write-bad-ptr.ck
+++ b/src/tests/userprog/write-bad-ptr.ck
@@ -2,12 +2,7 @@
 use strict;
 use warnings;
 use tests::tests;
-check_expected ([<<'EOF', <<'EOF']);
-(write-bad-ptr) begin
-(write-bad-ptr) open "sample.txt"
-(write-bad-ptr) end
-write-bad-ptr: exit(0)
-EOF
+check_expected ([<<'EOF']);
 (write-bad-ptr) begin
 (write-bad-ptr) open "sample.txt"
 write-bad-ptr: exit(-1)

From 6e59e8c9f3f183fd13287e510ac5955aa2df790d Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 16:22:16 +0000
Subject: [PATCH 02/11] Update validate_user_pointer to be a void function

---
 src/userprog/syscall.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index b1ce4cc..9d2521a 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -45,7 +45,7 @@ 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);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 typedef struct
@@ -401,7 +401,7 @@ fd_get_file (int fd)
    fully contained within user virtual memory. Kills the thread (by calling
    thread_exit) if the memory is invalid. Otherwise, returns the PTR given.
    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)
 {
   if (size > 0 && (ptr == NULL ||
@@ -409,6 +409,4 @@ validate_user_pointer (const void *ptr, size_t size)
                    !is_user_vaddr (ptr + size - 1) ||
                    pagedir_get_page (thread_current()->pagedir, ptr) == NULL))
     thread_exit ();
-
-  return (void *) ptr;
 }

From 26de38cdbad5fdc512eaee23afa19067552e3947 Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 16:39:45 +0000
Subject: [PATCH 03/11] Update validate_user_pointer to check if the memory
 block is mapped into a physical address

---
 src/userprog/syscall.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 9d2521a..9ddd6e9 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -45,7 +45,7 @@ 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 *start, size_t size);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 typedef struct
@@ -397,16 +397,24 @@ fd_get_file (int fd)
   return hash_entry (e, struct open_file, elem);
 }
 
-/* Validates if a block of memory starting at PTR and of size SIZE bytes is
+/* Validates if a block of memory starting at START and of size SIZE bytes is
    fully contained within user virtual memory. Kills the thread (by calling
-   thread_exit) if the memory is invalid. Otherwise, returns the PTR given.
-   If the size is 0, the function does no checks and returns PTR.*/
+   thread_exit) if the memory is invalid. Otherwise, returns (nothing) normally.
+   If the size is 0, the function does no checks and returns the given ptr. */
 static void
-validate_user_pointer (const void *ptr, size_t size)
+validate_user_pointer (const void *start, size_t size)
 {
-  if (size > 0 && (ptr == NULL ||
-                   !is_user_vaddr (ptr) ||
-                   !is_user_vaddr (ptr + size - 1) ||
-                   pagedir_get_page (thread_current()->pagedir, ptr) == NULL))
+  if (size == 0)
+    return;
+
+  const void *end = start + size - 1;
+
+  if (start == NULL || !is_user_vaddr (start) || !is_user_vaddr (end))
     thread_exit ();
+
+  /* We now need to check if the entire memory block is mapped to physical
+     memory by the page table. */
+  for (const void *ptr = start; ptr <= end; ptr += PGSIZE)
+    if (pagedir_get_page (thread_current ()->pagedir, ptr) == NULL)
+      thread_exit ();
 }

From eb4f23c2903380161bed75f01bb62fb7769ece6f Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 17:11:37 +0000
Subject: [PATCH 04/11] Add validate_user_string helper function to validate
 that a string is fully conatined within user vm

---
 src/userprog/syscall.c | 45 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 9ddd6e9..d60214d 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -46,6 +46,7 @@ static void syscall_close (int fd);
 
 static struct open_file *fd_get_file (int fd);
 static void validate_user_pointer (const void *start, size_t size);
+static void validate_user_string (const char *str);
 
 /* A struct defining a syscall_function pointer along with its arity. */
 typedef struct
@@ -140,7 +141,7 @@ syscall_exit (int status)
 static pid_t
 syscall_exec (const char *cmd_line)
 {
-  validate_user_pointer (cmd_line, 1);
+  validate_user_string (cmd_line);
 
   pid_t pid = process_execute(cmd_line);
 
@@ -159,9 +160,9 @@ syscall_wait (pid_t pid)
    pointer. Acquires the file system lock to prevent synchronisation issues,
    and then uses FILESYS_CREATE to create the file, returning the same status */
 static bool
-syscall_create (const char *file UNUSED, unsigned initial_size UNUSED)
+syscall_create (const char *file, unsigned initial_size)
 {
-  validate_user_pointer (file, 1);
+  validate_user_string (file);
 
   lock_acquire (&filesys_lock);
   bool status = filesys_create (file, initial_size);
@@ -176,7 +177,7 @@ 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);
 
   lock_acquire (&filesys_lock);
   bool status = filesys_remove (file);
@@ -192,7 +193,7 @@ syscall_remove (const char *file)
 static int
 syscall_open (const char *file)
 {
-  validate_user_pointer (file, 1);
+  validate_user_string (file);
 
   lock_acquire (&filesys_lock);
   struct file *ptr = filesys_open (file);
@@ -418,3 +419,37 @@ validate_user_pointer (const void *start, size_t size)
     if (pagedir_get_page (thread_current ()->pagedir, ptr) == NULL)
       thread_exit ();
 }
+
+/* Validates if a string is fully contained within user virtual memory. Kills
+   the thread (by calling thread_exit) if the memory is invalid. Otherwise,
+   returns (nothing) normally. */
+static void
+validate_user_string (const char *str)
+{
+  if (str == NULL || !is_user_vaddr (str))
+    thread_exit ();
+
+  size_t length = 0;
+  size_t offset = (uintptr_t) str % PGSIZE;
+
+  /* We move page by page, checking if the page is mapped to physical memory. */
+  for (;;)
+  {
+    void *page = pg_round_down (str + length);
+
+    if (!is_user_vaddr(page) ||
+        pagedir_get_page (thread_current ()->pagedir, page) == NULL)
+      thread_exit ();
+
+    while (offset < PGSIZE)
+      {
+        if (*str == '\0')
+          return; /* We reached the end of the string without issues. */
+
+        str++;
+        offset++;
+      }
+
+    offset = 0; /* Next page will start at the beginning. */
+  }
+}

From d890c2353ec0d40841241d049ed02c7af255dea9 Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 17:15:56 +0000
Subject: [PATCH 05/11] Add constant MAX_SYSCALL_ARGS to avoid magic numbers
 [Gleb]

---
 src/userprog/syscall.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index d60214d..0628c02 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -13,6 +13,8 @@
 #include <stdio.h>
 #include <syscall-nr.h>
 
+#define MAX_SYSCALL_ARGS 3
+
 static unsigned fd_counter = MIN_USER_FD;
 
 struct open_file
@@ -96,8 +98,8 @@ static void
 syscall_handler (struct intr_frame *f)
 {
   /* First, read the system call number from the stack. */
-  validate_user_pointer (f->esp, 1);
-  unsigned syscall_number = *(int *) f->esp;
+  validate_user_pointer (f->esp, sizeof (uintptr_t));
+  uintptr_t syscall_number = *(int *) f->esp;
 
   /* Ensures the number corresponds to a system call that can be handled. */
   if (syscall_number >= LOOKUP_SIZE)
@@ -108,9 +110,9 @@ 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));
-  uintptr_t args[3] = {0};
-  for (int i=0; i < syscall.arity; i++)
-      args[i] = *(uintptr_t *) (f->esp + sizeof (uintptr_t) * (i + 1));
+  uintptr_t args[MAX_SYSCALL_ARGS] = {0};
+  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
      there is a return value it is stored in f->eax. */

From 4f586bb4da29a5bd142bf83bdbd4c551faad651d Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 17:42:25 +0000
Subject: [PATCH 06/11] Fix Bug: Free all entries in the fd hashtable when the
 process exits, w/ E

---
 src/userprog/process.c |  5 +++++
 src/userprog/syscall.c | 14 ++++++++++++++
 src/userprog/syscall.h |  1 +
 3 files changed, 20 insertions(+)

diff --git a/src/userprog/process.c b/src/userprog/process.c
index 02adb34..c2076b2 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -325,6 +325,11 @@ process_exit (void)
   uint32_t *pd;
 
   printf ("%s: exit(%d)\n", cur->name, cur->exit_status);
+
+  /* Clean up all open files */
+  hash_destroy (&cur->open_files, fd_cleanup);
+
+  /* Close the executable file. */
   if (cur->exec_file != NULL)
     {
       lock_acquire (&filesys_lock);
diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 0628c02..daf6a8e 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -381,6 +381,20 @@ fd_less (const struct hash_elem *a_, const struct hash_elem *b_,
   return a->fd < b->fd;
 }
 
+/* Function to clean up an open file entry. Closes the file and frees the
+   associated memory. */
+void
+fd_cleanup (struct hash_elem *e, void *aux UNUSED)
+{
+  struct open_file *file_info = hash_entry (e, struct open_file, elem);
+
+  lock_acquire (&filesys_lock);
+  file_close (file_info->file);
+  lock_release (&filesys_lock);
+
+  free (file_info);
+}
+
 /* Gets a file from its descriptor (FD number). If there is no file with the fd
    FD it returns NULL. */
 static struct open_file *
diff --git a/src/userprog/syscall.h b/src/userprog/syscall.h
index 16af00c..681a8fb 100644
--- a/src/userprog/syscall.h
+++ b/src/userprog/syscall.h
@@ -14,5 +14,6 @@ void syscall_init (void);
 
 unsigned fd_hash (const struct hash_elem *element, void *aux);
 bool fd_less (const struct hash_elem *a, const struct hash_elem *b, void *aux);
+void fd_cleanup (struct hash_elem *e, void *aux);
 
 #endif /* userprog/syscall.h */

From 287130ca7b9186d6c7e43248ef45d39cb9478e4e Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 18:02:08 +0000
Subject: [PATCH 07/11] Update syscall.c to use syscall_exit on failure instead
 of calling thread_exit directly

---
 src/userprog/syscall.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index daf6a8e..85deffc 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -81,7 +81,6 @@ static const syscall_arguments syscall_lookup[] =
 static const int LOOKUP_SIZE
   = sizeof (syscall_lookup) / sizeof (syscall_arguments);
 
-
 /* Initialises the syscall handling system, as well as a global lock to
    synchronise all file access between processes. */
 void
@@ -103,13 +102,14 @@ syscall_handler (struct intr_frame *f)
 
   /* Ensures the number corresponds to a system call that can be handled. */
   if (syscall_number >= LOOKUP_SIZE)
-    thread_exit ();
+    syscall_exit (EXIT_FAILURE);
 
   syscall_arguments syscall = syscall_lookup[syscall_number];
 
   /* Next, read and copy the arguments from the stack pointer. */
   validate_user_pointer (f->esp + sizeof (uintptr_t),
                          syscall.arity * sizeof (uintptr_t));
+
   uintptr_t args[MAX_SYSCALL_ARGS] = {0};
   for (int i = 0; i < syscall.arity && i < MAX_SYSCALL_ARGS; i++)
     args[i] = *(uintptr_t *) (f->esp + sizeof (uintptr_t) * (i + 1));
@@ -427,13 +427,13 @@ validate_user_pointer (const void *start, size_t size)
   const void *end = start + size - 1;
 
   if (start == NULL || !is_user_vaddr (start) || !is_user_vaddr (end))
-    thread_exit ();
+    syscall_exit (EXIT_FAILURE);
 
   /* We now need to check if the entire memory block is mapped to physical
      memory by the page table. */
   for (const void *ptr = start; ptr <= end; ptr += PGSIZE)
     if (pagedir_get_page (thread_current ()->pagedir, ptr) == NULL)
-      thread_exit ();
+      syscall_exit (EXIT_FAILURE);
 }
 
 /* Validates if a string is fully contained within user virtual memory. Kills
@@ -443,7 +443,7 @@ static void
 validate_user_string (const char *str)
 {
   if (str == NULL || !is_user_vaddr (str))
-    thread_exit ();
+    syscall_exit (EXIT_FAILURE);
 
   size_t length = 0;
   size_t offset = (uintptr_t) str % PGSIZE;
@@ -455,7 +455,7 @@ validate_user_string (const char *str)
 
     if (!is_user_vaddr(page) ||
         pagedir_get_page (thread_current ()->pagedir, page) == NULL)
-      thread_exit ();
+      syscall_exit (EXIT_FAILURE);
 
     while (offset < PGSIZE)
       {

From b1c58194695b8321f532e9f715254c91f9cb6f6e Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 18:06:51 +0000
Subject: [PATCH 08/11] Avoid masking the struct syscall_arguments using
 typedef for consistency

---
 src/userprog/syscall.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 85deffc..34f85fe 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -14,6 +14,7 @@
 #include <syscall-nr.h>
 
 #define MAX_SYSCALL_ARGS 3
+#define EXIT_FAILURE -1
 
 static unsigned fd_counter = MIN_USER_FD;
 
@@ -51,15 +52,15 @@ static void validate_user_pointer (const void *start, size_t size);
 static void validate_user_string (const char *str);
 
 /* A struct defining a syscall_function pointer along with its arity. */
-typedef struct
+struct syscall_arguments
   {
     syscall_function function;    /* Function pointer. */
     int arity;                    /* Number of arguments of the function. */
-  } syscall_arguments;
+  };
 
 /* A look-up table mapping numbers to system call functions with their number of
    arguments. */
-static const syscall_arguments syscall_lookup[] =
+static const struct syscall_arguments syscall_lookup[] =
 {
   [SYS_HALT] = {(syscall_function) syscall_halt, 0},
   [SYS_EXIT] = {(syscall_function) syscall_exit, 1},
@@ -79,7 +80,7 @@ static const syscall_arguments syscall_lookup[] =
 /* The number of syscall functions (i.e, number of elements) within the
    syscall_lookup table. */
 static const int LOOKUP_SIZE
-  = sizeof (syscall_lookup) / sizeof (syscall_arguments);
+  = sizeof (syscall_lookup) / sizeof (struct syscall_arguments);
 
 /* Initialises the syscall handling system, as well as a global lock to
    synchronise all file access between processes. */
@@ -104,7 +105,7 @@ syscall_handler (struct intr_frame *f)
   if (syscall_number >= LOOKUP_SIZE)
     syscall_exit (EXIT_FAILURE);
 
-  syscall_arguments syscall = syscall_lookup[syscall_number];
+  struct syscall_arguments syscall = syscall_lookup[syscall_number];
 
   /* Next, read and copy the arguments from the stack pointer. */
   validate_user_pointer (f->esp + sizeof (uintptr_t),

From 9549ca28e5bacc08362047f8e79eea43b582f763 Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 18:18:41 +0000
Subject: [PATCH 09/11] Refactor syscall: Use EXIT_FAILURE instead of magic
 numbers & close files on failure

---
 src/userprog/syscall.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 34f85fe..0c352f5 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -138,7 +138,6 @@ syscall_exit (int status)
 }
 
 /* Executes a given command with the relevant args, by calling process_execute.
-   Acquires the filesystem lock as process_execute accesses the file system.
    Returns PID for the process that is running the CMD_LINE
  */
 static pid_t
@@ -146,9 +145,7 @@ syscall_exec (const char *cmd_line)
 {
   validate_user_string (cmd_line);
 
-  pid_t pid = process_execute(cmd_line);
-
-  return pid;
+  return process_execute (cmd_line); /* Returns the PID of the new process */
 }
 
 /* Handles the syscall of wait. Effectively a wrapper for process_wait as the
@@ -156,7 +153,7 @@ syscall_exec (const char *cmd_line)
 static int
 syscall_wait (pid_t pid)
 {
-  return process_wait (pid);
+  return process_wait (pid); /* Returns the exit status of the waited process */
 }
 
 /* Handles the syscall for file creation. First validates the user file
@@ -202,14 +199,17 @@ syscall_open (const char *file)
   struct file *ptr = filesys_open (file);
   lock_release (&filesys_lock);
   if (ptr == NULL)
-    return -1;
+    return EXIT_FAILURE;
 
   /* Allocate space for a struct representing a mapping from an FD to a struct
      file. */
   struct open_file *file_info
     = (struct open_file*) malloc (sizeof (struct open_file));
   if (file_info == NULL)
-    return -1;
+    {
+      file_close (ptr);
+      return EXIT_FAILURE;
+    }
 
   /* Populate the above struct, with a unique FD and the current open file */
   file_info->fd = fd_counter++;
@@ -230,7 +230,7 @@ syscall_filesize (int fd)
 {
   struct open_file *file_info = fd_get_file (fd);
   if (file_info == NULL)
-      return -1;
+      return EXIT_FAILURE;
 
   lock_acquire (&filesys_lock);
   int bytes = file_length (file_info->file);
@@ -249,7 +249,7 @@ syscall_read (int fd, void *buffer, unsigned size)
   /* Only console (fd = 0) or other files, not including STDOUT, (fd > 1) are
      allowed. */
   if (fd < 0 || fd == STDOUT_FILENO)
-    return -1;
+    return EXIT_FAILURE;
 
   validate_user_pointer (buffer, size);
 
@@ -267,7 +267,7 @@ syscall_read (int fd, void *buffer, unsigned size)
       /* Reading from a file. */
       struct open_file *file_info = fd_get_file (fd);
       if (file_info == NULL)
-        return -1;
+        return EXIT_FAILURE;
 
       lock_acquire (&filesys_lock);
       int bytes_written = file_read (file_info->file, buffer, size);

From 31ea2158052d99bec16aea64bf650ab38cf18a84 Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 18:30:24 +0000
Subject: [PATCH 10/11] Refactor validate_user_string to remove unnecessary
 variable to track length of str

---
 src/userprog/syscall.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index 0c352f5..a85fc2b 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -446,13 +446,12 @@ validate_user_string (const char *str)
   if (str == NULL || !is_user_vaddr (str))
     syscall_exit (EXIT_FAILURE);
 
-  size_t length = 0;
   size_t offset = (uintptr_t) str % PGSIZE;
 
   /* We move page by page, checking if the page is mapped to physical memory. */
   for (;;)
   {
-    void *page = pg_round_down (str + length);
+    void *page = pg_round_down (str);
 
     if (!is_user_vaddr(page) ||
         pagedir_get_page (thread_current ()->pagedir, page) == NULL)

From fa2fb4a711cbe6d63b4944481b57856fde9608bd Mon Sep 17 00:00:00 2001
From: sBubshait <s.bobshit@gmail.com>
Date: Wed, 13 Nov 2024 18:48:23 +0000
Subject: [PATCH 11/11] Refactor system call comments for accuracy and grammar

---
 src/userprog/syscall.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/userprog/syscall.c b/src/userprog/syscall.c
index a85fc2b..29231f3 100644
--- a/src/userprog/syscall.c
+++ b/src/userprog/syscall.c
@@ -91,7 +91,7 @@ syscall_init (void)
   lock_init (&filesys_lock);
 }
 
-/* Function that takes a interrupt frame containing a syscall and its args.
+/* Function that takes an interrupt frame containing a syscall and its args.
    Validates the arguments and pointers before calling the relevant
    high-level system call function, storing its output (if any) in f->eax */
 static void
@@ -138,8 +138,7 @@ syscall_exit (int status)
 }
 
 /* Executes a given command with the relevant args, by calling process_execute.
-   Returns PID for the process that is running the CMD_LINE
- */
+   Returns PID for the process that is running the CMD_LINE. */
 static pid_t
 syscall_exec (const char *cmd_line)
 {
@@ -416,8 +415,8 @@ fd_get_file (int fd)
 }
 
 /* Validates if a block of memory starting at START and of size SIZE bytes is
-   fully contained within user virtual memory. Kills the thread (by calling
-   thread_exit) if the memory is invalid. Otherwise, returns (nothing) normally.
+   fully contained within user virtual memory. Kills the thread (by exiting with
+   failure) if the memory is invalid. Otherwise, returns (nothing) normally.
    If the size is 0, the function does no checks and returns the given ptr. */
 static void
 validate_user_pointer (const void *start, size_t size)
@@ -438,7 +437,7 @@ validate_user_pointer (const void *start, size_t size)
 }
 
 /* Validates if a string is fully contained within user virtual memory. Kills
-   the thread (by calling thread_exit) if the memory is invalid. Otherwise,
+   the thread (by exiting with failure) if the memory is invalid. Otherwise,
    returns (nothing) normally. */
 static void
 validate_user_string (const char *str)