UML - Don't allow processes to call into stub

Kill a process that tries to branch into a stub and execute a system call. There are no security implications here - a system call in a stub is treated the same as a system call anywhere else. But if a process is trying to branch into a stub, either it is trying something nasty or it has gone haywire, so it's a good idea to get rid of it in either case.

---
 arch/um/os-Linux/skas/process.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6.22/arch/um/os-Linux/skas/process.c
===================================================================
@@ -146,6 +146,9 @@ static void handle_trap(int pid, struct 
 {
 	int err, status;
 
+	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
+		fatal_sigsegv();
+
 	/* Mark this as a syscall */
 	UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);