lguest: fix sense if IF flag on interrupt injection

The sense of the IF bit is backwards in the host interrupt handling.

This means we always save "IF=1" on the stack when injecting an
interrupt.  It turns out this is almost always correct (unless the
guest is taking a page fault in an interrupt due to an unpopulated
vmalloc mapping), so went unnoticed.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index d9de5bbc613f3e06431ddbbe5e7dc4d257f370f3..bee029bb2c7bf543912f97d1fa798739569e2606 100644 (file)
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -38,12 +38,12 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err)
                ss = lg->regs->ss;
        }
 
-       /* We use IF bit in eflags to indicate whether irqs were disabled
-          (it's always 0, since irqs are enabled when guest is running). */
+       /* We use IF bit in eflags to indicate whether irqs were enabled
+          (it's always 1, since irqs are enabled when guest is running). */
        eflags = lg->regs->eflags;
-       if (get_user(irq_enable, &lg->lguest_data->irq_enabled))
-               irq_enable = 0;
-       eflags |= (irq_enable & X86_EFLAGS_IF);
+       if (get_user(irq_enable, &lg->lguest_data->irq_enabled) == 0
+           && !(irq_enable & X86_EFLAGS_IF))
+               eflags &= ~X86_EFLAGS_IF;
 
        push_guest_stack(lg, &gstack, eflags);
        push_guest_stack(lg, &gstack, lg->regs->cs);