CVE-2019-18423

high

Description

An issue was discovered in Xen through 4.12.x allowing ARM guest OS users to cause a denial of service via a XENMEM_add_to_physmap hypercall. p2m->max_mapped_gfn is used by the functions p2m_resolve_translation_fault() and p2m_get_entry() to sanity check guest physical frame. The rest of the code in the two functions will assume that there is a valid root table and check that with BUG_ON(). The function p2m_get_root_pointer() will ignore the unused top bits of a guest physical frame. This means that the function p2m_set_entry() will alias the frame. However, p2m->max_mapped_gfn will be updated using the original frame. It would be possible to set p2m->max_mapped_gfn high enough to cover a frame that would lead p2m_get_root_pointer() to return NULL in p2m_get_entry() and p2m_resolve_translation_fault(). Additionally, the sanity check on p2m->max_mapped_gfn is off-by-one allowing "highest mapped + 1" to be considered valid. However, p2m_get_root_pointer() will return NULL. The problem could be triggered with a specially crafted hypercall XENMEM_add_to_physmap{, _batch} followed by an access to an address (via hypercall or direct access) that passes the sanity check but cause p2m_get_root_pointer() to return NULL. A malicious guest administrator may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen version 4.8 and newer are vulnerable. Only Arm systems are vulnerable. x86 systems are not affected.

References

http://www.openwall.com/lists/oss-security/2019/10/31/4

http://xenbits.xen.org/xsa/advisory-301.html

https://lists.fedoraproject.org/archives/list/[email protected]/message/2BQKX7M2RHCWDBKNPX4KEBI3MJIH6AYZ/

https://lists.fedoraproject.org/archives/list/[email protected]/message/I5WWPW4BSZDDW7VHU427XTVXV7ROOFFW/

https://lists.fedoraproject.org/archives/list/[email protected]/message/IZYATWNUGHRBG6I3TC24YHP5Y3J7I6KH/

https://seclists.org/bugtraq/2020/Jan/21

https://security.gentoo.org/glsa/202003-56

https://www.debian.org/security/2020/dsa-4602

Details

Source: MITRE

Published: 2019-10-31

Updated: 2020-08-24

Type: CWE-193

Risk Information

CVSS v2

Base Score: 8.5

Vector: AV:N/AC:M/Au:S/C:C/I:C/A:C

Impact Score: 10

Exploitability Score: 6.8

Severity: HIGH

CVSS v3

Base Score: 8.8

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Impact Score: 5.9

Exploitability Score: 2.8

Severity: HIGH