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>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index d9de5bbc613f..bee029bb2c7b 100644
--- 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);