Xen is a bare-metal hypervisor.
In CIRRUS_BLTMODE_MEMSYSSRC mode the bitblit copy routine cirrus_bitblt_cputovideo fails to check wethehr the specified memory region is safe.
A local attacker could potentially execute arbitrary code with privileges of Xen (QEMU) process on the host, gain privileges on the host system, or cause a Denial of Service condition.
Running guests in Paravirtualization (PV) mode, or running guests in Hardware-assisted virtualizion (HVM) utilizing stub domains mitigate 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.
All Xen Tools users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose ">=app-emulation/xen-tools-4.7.1-r8"