Adjust the fix in r236953, by not generating the signal manually, but

performing the return to usermode using full return path.  This
consolidates the handling of exceptional situations in less number of
places, and is less code as well.

Reviewed by:   jhb
MFC after:     1 week

1 files changed, 5 insertions, 11 deletions

diff --git a/sys/amd64/amd64/trap.c b/sys/amd64/amd64/trap.c
index 4216fd3..75e15e0 100644
--- a/sys/amd64/amd64/trap.c
+++ b/sys/amd64/amd64/trap.c
@@ -977,16 +977,10 @@ amd64_syscall(struct thread *td, int traced)
 	 * If the user-supplied value of %rip is not a canonical
 	 * address, then some CPUs will trigger a ring 0 #GP during
 	 * the sysret instruction.  However, the fault handler would
-	 * execute with the user's %gs and %rsp in ring 0 which would
-	 * not be safe.  Instead, preemptively kill the thread with a
-	 * SIGBUS.
+	 * execute in ring 0 with the user's %gs and %rsp which would
+	 * not be safe.  Instead, use the full return path which
+	 * catches the problem safely.
 	 */
-	if (td->td_frame->tf_rip >= VM_MAXUSER_ADDRESS) {
-		ksiginfo_init_trap(&ksi);
-		ksi.ksi_signo = SIGBUS;
-		ksi.ksi_code = BUS_OBJERR;
-		ksi.ksi_trapno = T_PROTFLT;
-		ksi.ksi_addr = (void *)td->td_frame->tf_rip;
-		trapsignal(td, &ksi);
-	}
+	if (td->td_frame->tf_rip >= VM_MAXUSER_ADDRESS)
+		set_pcb_flags(td->td_pcb, PCB_FULL_IRET);
 }