lguest: fix guest kernel stack overflow when TF bit set.
The symptoms are that running gdb on a binary causes the guest to
overflow the kernels stack (after some period of time), resulting in
it finally being killed with a "Bad address" message.
Reported-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index 28433a1..70dfcdc 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -140,6 +140,16 @@
cpu->regs->eip = idt_address(lo, hi);
/*
+ * Trapping always clears these flags:
+ * TF: Trap flag
+ * VM: Virtual 8086 mode
+ * RF: Resume
+ * NT: Nested task.
+ */
+ cpu->regs->eflags &=
+ ~(X86_EFLAGS_TF|X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT);
+
+ /*
* There are two kinds of interrupt handlers: 0xE is an "interrupt
* gate" which expects interrupts to be disabled on entry.
*/