CVE-2019-18423

NameCVE-2019-18423
DescriptionAn 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.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub code/issues, web search, more)
ReferencesDSA-4602-1
NVD severityhigh
Debian Bugs947944

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
xen (PTS)jessie4.4.1-9+deb8u10vulnerable
jessie (security)4.4.4lts5-0+deb8u1vulnerable
stretch (security), stretch4.8.5.final+shim4.10.4-1+deb9u12fixed
buster, buster (security)4.11.3+24-g14b62ab3e5-1~deb10u1fixed
bullseye, sid4.11.3+24-g14b62ab3e5-1fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
xensource(unstable)4.11.3+24-g14b62ab3e5-1947944
xensourcebuster4.11.3+24-g14b62ab3e5-1~deb10u1DSA-4602-1
xensourcejessie(unfixed)end-of-life
xensourcestretch4.8.5.final+shim4.10.4-1+deb9u12DSA-4602-1

Notes

[jessie] - xen <end-of-life> (Not supported in jessie LTS)
https://xenbits.xen.org/xsa/advisory-301.html

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