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Date: Sat, 11 Feb 2017 08:49:54 +0000
From: Roger Pau Monné <>
To: security team <>
CC: <>, <>,
	<>, <>
Subject: Re: [Xen-users] Xen Security Advisory 208 (CVE-2017-2615) - oob
 access in cirrus bitblt copy

On Fri, Feb 10, 2017 at 12:43:17PM +0000, security team wrote:
> Hash: SHA1
>             Xen Security Advisory CVE-2017-2615 / XSA-208
>                    oob access in cirrus bitblt copy
> =================
> When doing bitblt copy backwards, qemu should negate the blit width.
> This avoids an oob access before the start of video memory.
> ======
> A malicious guest administrator can cause an out of bounds memory
> access, possibly leading to information disclosure or privilege
> escalation.
> ==================
> Versions of qemu shipped with all Xen versions are vulnerable.
> Xen systems running on x86 with HVM guests, with the qemu process
> running in dom0 are vulnerable.
> Only guests provided with the "cirrus" emulated video card can exploit
> the vulnerability.  The non-default "stdvga" emulated video card is
> not vulnerable.  (With xl the emulated video card is controlled by the
> "stdvga=" and "vga=" domain configuration options.)
> ARM systems are not vulnerable.  Systems using only PV guests are not
> vulnerable.
> For VMs whose qemu process is running in a stub domain, a successful
> attacker will only gain the privileges of that stubdom, which should
> be only over the guest itself.
> Both upstream-based versions of qemu (device_model_version="qemu-xen")
> and `traditional' qemu (device_model_version="qemu-xen-traditional")
> are vulnerable.
> ==========
> Running only PV guests will avoid the issue.
> Running HVM guests with the device model in a stubdomain will mitigate
> the issue.
> Changing the video card emulation to stdvga (stdvga=1, vga="stdvga",
> in the xl domain configuration) will avoid the vulnerability.
> ==========
> Applying the appropriate attached patch resolves this issue.
> xsa208-qemuu.patch    qemu-xen, mainline qemu

The patch doesn't apply cleanly against the QEMU-upstream found in Xen 4.7.1:


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