Index: trap.c
===================================================================
--- trap.c	(revision 5952)
+++ trap.c	(working copy)
@@ -13,10 +13,13 @@
 #include <kern/prof.h>
 #include <kern/arch.h>
 #include <inc/error.h>
+#include <inc/setjmp.h>
+#include <inc/safeint.h>
 
 static uint64_t trap_user_iret_tsc;
 static const struct Thread *trap_thread;
 static int trap_thread_syscall_writeback;
+static struct jos_jmp_buf *trap_jb;
 
 static struct {
     char trap_entry_code[16] __attribute__ ((aligned (16)));
@@ -180,6 +183,9 @@
     tf->tf_fs = read_fs();
     tf->tf_gs = read_gs();
 
+    if (trap_jb)
+	jos_longjmp(trap_jb, 1);
+
     cyg_profile_free_stack(read_rsp());
 
     if (trap_thread) {
@@ -393,3 +399,25 @@
   TF_DEF (tf_gs);
   TF_DEF (tf__trapentry_rip);
 }
+
+int
+memcpy_from_user(void *dst, const void *src, uint64_t len)
+{
+    int overflow = 0;
+    uintptr_t start = (uintptr_t) src;
+    uintptr_t end   = safe_addptr(&overflow, start, len);
+    if (overflow || end >= ULIM)
+	return -E_INVAL;
+
+    struct jos_jmp_buf jb;
+    if (jos_setjmp(&jb) != 0) {
+	int r = check_user_access((char*) src, len, 0);
+	if (r < 0)
+	    return r;
+    }
+
+    trap_jb = &jb;
+    memcpy(dst, src, len);
+    trap_jb = 0;
+    return 0;
+}