KVM: emulator: Fix permission checking in io permission bitmap

Currently if io port + len crosses 8bit boundary in io permission bitmap the
check may allow IO that otherwise should not be allowed. The patch fixes that.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index d6088b8686fb..0ad47b819a8b 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1769,8 +1769,7 @@ static bool emulator_io_port_access_allowed(struct x86_emulate_ctxt *ctxt,
         struct desc_struct tr_seg;
         u32 base3;
         int r;
-        u16 io_bitmap_ptr;
-        u8 perm, bit_idx = port & 0x7;
+        u16 io_bitmap_ptr, perm, bit_idx = port & 0x7;
         unsigned mask = (1 << len) - 1;
         unsigned long base;
 
@@ -1788,7 +1787,7 @@ static bool emulator_io_port_access_allowed(struct x86_emulate_ctxt *ctxt,
                 return false;
         if (io_bitmap_ptr + port/8 > desc_limit_scaled(&tr_seg))
                 return false;
-        r = ops->read_std(base + io_bitmap_ptr + port/8, &perm, 1, ctxt->vcpu,
+        r = ops->read_std(base + io_bitmap_ptr + port/8, &perm, 2, ctxt->vcpu,
                           NULL);
         if (r != X86EMUL_CONTINUE)
                 return false;