linux-kernel - [PATCH 3.2 88/94] KVM: VMX: remove I/O port 0x80 bypass on Intel hosts

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Message-ID: <lsq.1514480352.862421124@decadent.org.uk>
Date:   Thu, 28 Dec 2017 16:59:12 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Radim Krčmář" <rkrcmar@...hat.com>,
        "Jim Mattson" <jmattson@...gle.com>,
        "Andrew Honig" <ahonig@...gle.com>
Subject: [PATCH 3.2 88/94] KVM: VMX: remove I/O port 0x80 bypass on Intel
 hosts

3.2.97-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Honig <ahonig@...gle.com>

commit d59d51f088014f25c2562de59b9abff4f42a7468 upstream.

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@...gle.com>
Signed-off-by: Jim Mattson <jmattson@...gle.com>
Fixes: fdef3ad1b386 ("KVM: VMX: Enable io bitmaps to avoid IO port 0x80 VMEXITs")
Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/vmx.c | 5 -----
 1 file changed, 5 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7285,12 +7285,7 @@ static int __init vmx_init(void)
 		goto out2;
 	}

-	/*
-	 * 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);