KVM: VMX: remove I/O port 0x80 bypass on Intel hosts

This fixes CVE-2017-1000407.

KVM allows guests to directly access I/O port 0x80 on Intel hosts.  If
the guest floods this port with writes it generates exceptions and
instability in the host kernel, leading to a crash.  With this change
guest writes to port 0x80 on Intel will behave the same as they
currently behave on AMD systems.

Prevent the flooding by removing the code that sets port 0x80 as a
passthrough port.  This is essentially the same as upstream patch
99f85a28a78e96d28907fe036e1671a218fee597, except that patch was
for AMD chipsets and this patch is for Intel.

Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Fixes: fdef3ad1b386 ("KVM: VMX: Enable io bitmaps to avoid IO port 0x80 VMEXITs")
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Gbp-Pq: Topic bugfix/x86
Gbp-Pq: Name kvm-vmx-remove-i-o-port-0x80-bypass-on-intel-hosts.patch

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a8ae57acb6f63a0beaf4d16222365c4ed8001a86..40a2254f4dc9dd2d0753f16b9547c091f31a308f 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6411,12 +6411,7 @@ static __init int hardware_setup(void)
        memset(vmx_vmread_bitmap, 0xff, PAGE_SIZE);
        memset(vmx_vmwrite_bitmap, 0xff, PAGE_SIZE);
 
-       /*
-        * Allow direct access to the PC debug port (it is often used for I/O
-        * delays, but the vmexits simply slow things down).
-        */
        memset(vmx_io_bitmap_a, 0xff, PAGE_SIZE);
-       clear_bit(0x80, vmx_io_bitmap_a);
 
        memset(vmx_io_bitmap_b, 0xff, PAGE_SIZE);