diff -Naur -X exclude-files ac_cur/arch/um/include/kern_util.h ac/arch/um/include/kern_util.h
--- ac_cur/arch/um/include/kern_util.h	Sat Sep 15 15:56:11 2001
+++ ac/arch/um/include/kern_util.h	Sat Sep 15 20:04:54 2001
@@ -35,7 +35,8 @@
 extern int is_stack_fault(unsigned long sp);
 extern unsigned long segv(unsigned long address, unsigned long ip, 
 			  int is_write, int is_user);
-extern int set_user_thread(void *task, int on, int restore_regs);
+extern int set_user_thread(void *task, int on, int restore_regs, 
+			   int protect_mem);
 extern void syscall_ready(void);
 extern void set_tracing(void *t, int tracing);
 extern int is_tracing(void *task);
@@ -120,6 +121,8 @@
 extern int config_gdb(char *str);
 extern int remove_gdb(void);
 extern char *uml_strdup(char *string);
+extern void unprotect_kernel_mem(void);
+extern void protect_kernel_mem(void);
 #endif
 
 /*
diff -Naur -X exclude-files ac_cur/arch/um/kernel/exec_kern.c ac/arch/um/kernel/exec_kern.c
--- ac_cur/arch/um/kernel/exec_kern.c	Sat Sep 15 15:56:11 2001
+++ ac/arch/um/kernel/exec_kern.c	Sat Sep 15 20:04:54 2001
@@ -114,7 +114,7 @@
 
 int um_execve(char *file, char **argv, char **env)
 {
-	if(execve1(file, argv, env) == 0) set_user_thread(current, 1, 1);
+	if(execve1(file, argv, env) == 0) set_user_thread(current, 1, 1, 1);
 	return(-1);
 }
 
diff -Naur -X exclude-files ac_cur/arch/um/kernel/process_kern.c ac/arch/um/kernel/process_kern.c
--- ac_cur/arch/um/kernel/process_kern.c	Sat Sep 15 19:23:51 2001
+++ ac/arch/um/kernel/process_kern.c	Sat Sep 15 20:06:04 2001
@@ -64,7 +64,7 @@
 	init_task.thread.extern_pid = pid;
 }
 
-int set_user_thread(void *t, int on, int restore_regs)
+int set_user_thread(void *t, int on, int restore_regs, int protect_mem)
 {
 	struct task_struct *task;
 	int ret;
@@ -75,6 +75,7 @@
 	ret = task->thread.tracing;
 	task->thread.request.op = on ? OP_TRACE_ON : OP_TRACE_OFF;
 	task->thread.request.u.tracing.restore_regs = restore_regs;
+	if(on && protect_mem) protect_kernel_mem();
 	usr1_pid(getpid());
 	return(ret);
 }
@@ -807,6 +808,26 @@
 	if(new == NULL) return(NULL);
 	strcpy(new, string);
 	return(new);
+}
+
+void unprotect_kernel_mem(void)
+{
+	unsigned long start_stack, end_stack;
+
+	start_stack = (unsigned long) current;
+	end_stack = start_stack + PAGE_SIZE * 4;
+	protect(physmem, start_stack - physmem, 1, 1, 1);
+	protect(end_stack, high_physmem - end_stack, 1, 1, 1);
+}
+
+void protect_kernel_mem(void)
+{
+	unsigned long start_stack, end_stack;
+
+	start_stack = (unsigned long) current;
+	end_stack = start_stack + PAGE_SIZE * 4;
+	protect(physmem, start_stack - physmem, 1, 1, 1);
+	protect(end_stack, high_physmem - end_stack, 1, 1, 1);
 }
 
 /*
diff -Naur -X exclude-files ac_cur/arch/um/kernel/syscall_user.c ac/arch/um/kernel/syscall_user.c
--- ac_cur/arch/um/kernel/syscall_user.c	Sat Sep 15 15:56:11 2001
+++ ac/arch/um/kernel/syscall_user.c	Sat Sep 15 20:13:58 2001
@@ -65,6 +65,7 @@
 	int index, syscall, again;
 
 	kill(getpid(), SIGSTOP);
+	unprotect_kernel_mem();
 	timer_ready = 1;
 	syscall_trace();
 	lock_syscall();
@@ -94,7 +95,7 @@
 	 * This is a race, set_user_thread has to be called with signals off
 	 */
 	timer_ready = 0;
-	set_user_thread(NULL, 1, 1);
+	set_user_thread(NULL, 1, 1, 1);
 	return(0);
 }
 
diff -Naur -X exclude-files ac_cur/arch/um/kernel/trap_user.c ac/arch/um/kernel/trap_user.c
--- ac_cur/arch/um/kernel/trap_user.c	Sat Sep 15 15:56:11 2001
+++ ac/arch/um/kernel/trap_user.c	Sat Sep 15 20:04:54 2001
@@ -329,10 +329,11 @@
 	if(user_mode) interrupt_end();
 	block_signals();
 	change_sig(SIGUSR1, 0);
-	set_user_thread(NULL, user_mode, 0);
+	set_user_thread(NULL, user_mode, 0, 0);
 	errno = save_errno;
 	if(user_mode) timer_ready = 0;
 	timer_on = save_timer;
+	if(user_mode) protect_kernel_mem();
 }
 
 void sig_handler(int sig, struct sigcontext sc)
@@ -348,10 +349,11 @@
 	if(user_mode) interrupt_end();
 	block_signals();
 	change_sig(SIGUSR1, 0);
-	set_user_thread(NULL, user_mode, 0);
+	set_user_thread(NULL, user_mode, 0, 0);
 	errno = save_errno;
 	if(user_mode) timer_ready = 0;
 	timer_on = save_timer;
+	if(user_mode) protect_kernel_mem();
 }
 
 extern int timer_irq_inited, missed_ticks;