Information

Advisory

XSA-360

Public release

2021-01-21 14:09

Updated

2021-01-26 22:03

Version

2

CVE(s)

CVE-2021-3308

Title

IRQ vector leak on x86

Filesadvisory-360.txt (signed advisory file)
xsa360.meta
xsa360.patch
xsa360-4.14.patchAdvisory

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256

        Xen Security Advisory CVE-2021-3308 / XSA-360
                          version 2

                    IRQ vector leak on x86

UPDATES IN VERSION 2

CVE assigned.

ISSUE DESCRIPTION

An x86 HVM guest with PCI pass through devices can force the allocation of all IDT vectors on the system by rebooting itself with MSI or MSI-X capabilities enabled and entries setup.

Such reboots will leak any vectors used by the MSI(-X) entries that the guest might had enabled, and hence will lead to vector exhaustion on the system, not allowing further PCI pass through devices to work properly.

IMPACT

HVM guests with PCI pass through devices can mount a Denial of Service (DoS) attack affecting the pass through of PCI devices to other guests or the hardware domain. In the latter case this would affect the entire host.

VULNERABLE SYSTEMS

Xen versions 4.12.3, 4.12.4, and all versions from 4.13.1 onwards are vulnerable. Xen version 4.13.0 and all versions up to 4.12.2 are not affected.

Only x86 systems running HVM guests with PCI pass through devices are vulnerable.

MITIGATION

Not running HVM guests with PCI pass through devices will avoid the vulnerability. Note that even non-malicious guests can trigger this vulnerability as part of normal operation.

RESOLUTION

Applying the appropriate attached patch resolves this issue.

Note that patches for released versions are generally prepared to apply to the stable branches, and may not apply cleanly to the most recent release tarball. Downstreams are encouraged to update to the tip of the stable branch before applying these patches.

xsa360.patch xen-unstable xsa360-4.14.patch Xen 4.14 - 4.12

$ sha256sum xsa360* c874ad2b9edb0791ac975735306d055b1916f4acbc59e6f1550fbf33223d6106 xsa360.meta 592f3afda63777d31844e0e34d85fbe387a62d59fa7903ee19b22a98fba68894 xsa360.patch 809515011efb781a2a8742e9acfd76412d3920c2d4142bb187588cd36f77383e xsa360-4.14.patch $

CREDITS

This issue was discovered by James McCoy, debugged in combination with Samuel Verschelde of Vates, and recognised as a security issue by Roger Pau Monné of Citrix.

NOTE REGARDING LACK OF EMBARGO

This was reported and debugged publicly, before the security implications were apparent. -----BEGIN PGP SIGNATURE-----

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Xenproject.org Security Team