Commit d59d51f0 authored Dec 01, 2017 by Andrew Honig Committed by Radim Krčmář Dec 05, 2017

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
99f85a28, 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: fdef3ad1 ("KVM: VMX: Enable io bitmaps to avoid IO port 0x80 VMEXITs")
Cc: <stable@vger.kernel.org>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

parent 6ab0b9fe

arch/x86/kvm/vmx.c

+0 −5

Original line number	Diff line number	Diff line
		@@ -6755,12 +6755,7 @@ 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);

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