[PATCH v4 1/4] syscalls: Restore address limit after a syscall

On 03/22/17 13:44, Andy Lutomirski wrote:

While it's possible that silently papering over the bug is slightly
faster than BUGging, it will allow bugs to continue to exist
undetected.

It would also allow the test to be inlined (at least on architectures
which have a one-site implementation) and have only the failure case out
of line, with a __noreturn annotation (which allows it to be jumped to
rather than called, which is usually available as a conditional
operation whereas call often isn't.)

That is...

extern void __noreturn __pre_usermode_state_invalid(void);

static void verify_pre_usermode_state(void)
{
	if (unlikely(!segment_eq(get_fs(), USER_DS))
		__pre_usermode_state_invalid();
}

	-hpa