The Ocaml xenstored implementation (oxenstored) in Xen 4.1.x, 4.2.x, and 4.3.x allows local guest domains to cause a denial of service (domain shutdown) via a large message reply.

ISSUE DESCRIPTION =================

Guests are currently permitted to modify all of the (writable) bits in the PCI command register of devices passed through to them. This in particular allows them to disable memory and I/O decoding on the device unless the device is an SR-IOV virtual function, in which case subsequent accesses to the respective MMIO or I/O port ranges would - - on PCI Express devices - lead to Unsupported Request responses. The treatmeant of such errors is platform specific.

IMPACT ======

In the event that the platform surfaces aforementioned UR responses as Non-Maskable Interrupts, and either the OS is configured to treat NMIs as fatal or (e.g. via ACPI's APEI) the platform tells the OS to treat these errors as fatal, the host would crash, leading to a Denial of Service.

VULNERABLE SYSTEMS ==================

Xen versions 3.3 and onwards are vulnerable due to supporting PCI pass-through. Upstream Linux versions 3.1 and onwards are vulnerable due to supporting PCI backend functionality. Other Linux versions as well as other OS versions may be vulnerable too.

Any domain which is given access to a non-SR-IOV virtual function PCI Express device can take advantage of this vulnerability.

MITIGATION ==========

This issue can be avoided by not assigning PCI Express devices other than SR-IOV virtual functions to untrusted guests.

RESOLUTION ==========

Applying the attached patch resolves this issue for upstream Linux.

xsa120.patch Linux 3.19

$ sha256sum xsa120.patch 5167215293d4a8a05f090fca5b20eb5878213a0158a0e7a12c245553db81a855 xsa120.patch

Last updated 24 July 2024

Xen 3.0.3 through 4.1.x (possibly 4.1.6.1), 4.2.x (possibly 4.2.3), and 4.3.x (possibly 4.3.1) does not properly prevent access to hypercalls, which allows local guest users to gain privileges via a crafted application running in ring 1 or 2.

Xen 4.2.x and 4.3.x, when nested virtualization is disabled, does not properly check the emulation paths for (1) VMLAUNCH and (2) VMRESUME, which allows local HVM guest users to cause a denial of service (host crash) via unspecified vectors related to "guest VMX instruction execution."

The XENDOMCTLgetmemlist hypercall in Xen 3.4.x through 4.3.x (possibly 4.3.1) does not always obtain the pagealloclock and mmrwlock in the same order, which allows local guest administrators to cause a denial of service (host deadlock).

Use-after-free vulnerability in the libxllistcpupool function in the libxl toolstack library in Xen 4.2.x and 4.3.x, when running "under memory pressure," returns the original pointer when the realloc function fails, which allows local users to cause a denial of service (heap corruption and crash) and possibly execute arbitrary code via unspecified vectors.

The outs instruction emulation in Xen 3.1.x, 4.2.x, 4.3.x, and earlier, when using FS: or GS: segment override, uses an uninitialized variable as a segment base, which allows local 64-bit PV guests to obtain sensitive information (hypervisor stack content) via unspecified vectors related to stale data in a segment register.

The xenlight library (libxl) in Xen 4.0.x through 4.2.x, when IOMMU is disabled, provides access to a busmastering-capable PCI passthrough device before the IOMMU setup is complete, which allows local HVM guest domains to gain privileges or cause a denial of service via a DMA instruction.

The ocaml binding for the xcvcpugetaffinity function in Xen 4.2.x and 4.3.x frees certain memory that may still be intended for use, which allows local users to cause a denial of service (heap corruption and crash) and possibly execute arbitrary code via unspecified vectors that trigger a (1) use-after-free or (2) double free.

The xluvifparserate function in the libxlu library in Xen 4.2.x and 4.3.x allows local users to cause a denial of service (NULL pointer dereference) by using the "@" character as the VIF rate configuration.

Xen 4.3.x and earlier does not properly handle certain errors, which allows local HVM guests to obtain hypervisor stack memory via a (1) port or (2) memory mapped I/O write or (3) other unspecified operations related to addresses without associated memory.

The qdisk PV disk backend in qemu-xen in Xen 4.2.x and 4.3.x before 4.3.1, and qemu 1.1 and other versions, allows local HVM guests to cause a denial of service (domain grant reference consumption) via unspecified vectors.

The dommuupdate function in arch/x86/mm.c in Xen 3.2.x through 4.4.x does not properly manage page references, which allows remote domains to cause a denial of service by leveraging control over an HVM guest and a crafted MMUMACHPHYSUPDATE.

The compatibility mode hypercall argument translation in Xen 3.3.x through 4.4.x, when running on a 64-bit hypervisor, allows local 32-bit HVM guests to cause a denial of service (host crash) via vectors involving altering the high halves of registers while in 64-bit mode.

The dommuupdate function in arch/x86/mm.c in Xen 4.x through 4.4.x does not properly restrict updates to only PV page tables, which allows remote PV guests to cause a denial of service (NULL pointer dereference) by leveraging hardware emulation services for HVM guests using Hardware Assisted Paging (HAP).

arch/x86/x86emulate/x86emulate.c in Xen 3.2.1 through 4.4.x does not properly check privileges, which allows local HVM guest users to gain privileges or cause a denial of service (crash) via a crafted (1) CALL, (2) JMP, (3) RETF, (4) LCALL, (5) LJMP, or (6) LRET far branch instruction.

The x86emulate function in arch/x86/x86emulate/x86emulate.c in Xen 3.3.x through 4.4.x does not check the supervisor mode permissions for instructions that generate software interrupts, which allows local HVM guest users to cause a denial of service (guest crash) via unspecified vectors.

Race condition in HVMOPtrackdirtyvram in Xen 4.0.0 through 4.4.x does not ensure possession of the guarding lock for dirty video RAM tracking, which allows certain local guest domains to cause a denial of service via unspecified vectors.

The x86emulate function in arch/x86/x86emulate/x86emulate.c in Xen 4.4.x and earlier does not properly check supervisor mode permissions, which allows local HVM users to cause a denial of service (guest crash) or gain guest kernel mode privileges via vectors involving an (1) HLT, (2) LGDT, (3) LIDT, or (4) LMSW instruction.

The hvmmsrreadintercept function in arch/x86/hvm/hvm.c in Xen 4.1 through 4.4.x uses an improper MSR range for x2APIC emulation, which allows local HVM guests to cause a denial of service (host crash) or read data from the hypervisor or other guests via unspecified vectors.

Certain MMU virtualization operations in Xen 4.2.x through 4.4.x before the xsa97-hap patch, when using Hardware Assisted Paging (HAP), are not preemptible, which allows local HVM guest to cause a denial of service (vcpu consumption) by invoking these operations, which process every page assigned to a guest, a different vulnerability than CVE-2014-5149.

Certain MMU virtualization operations in Xen 4.2.x through 4.4.x, when using shadow pagetables, are not preemptible, which allows local HVM guest to cause a denial of service (vcpu consumption) by invoking these operations, which process every page assigned to a guest, a different vulnerability than CVE-2014-5146.

The memoryexchange function in common/memory.c in Xen 3.2.x through 4.6.x does not properly release locks, which might allow guest OS administrators to cause a denial of service (deadlock or host crash) via unspecified vectors, related to XENMEMexchange error handling.

The libxl toolstack library in Xen 4.1.x through 4.6.x does not properly release mappings of files used as kernels and initial ramdisks when managing multiple domains in the same process, which allows attackers to cause a denial of service (memory and disk consumption) by starting domains.

The memoryexchange function in common/memory.c in Xen 3.2.x through 4.6.x does not properly hand back pages to a domain, which might allow guest OS administrators to cause a denial of service (host crash) via unspecified vectors related to domain teardown.

The (1) libxlsetmemorytarget function in tools/libxl/libxl.c and (2) libxlbuildpost function in tools/libxl/libxldom.c in Xen 3.4.x through 4.6.x do not properly calculate the balloon size when using the populate-on-demand (PoD) system, which allows local HVM guest users to cause a denial of service (guest crash) via unspecified vectors related to "heavy memory pressure."

Multiple memory leaks in Xen 4.0 through 4.6.x allow local guest administrators or domains with certain permission to cause a denial of service (memory consumption) via a large number of "teardowns" of domains with the vcpu pointer array allocated using the (1) XENDOMCTLmaxvcpus hypercall or the xenoprofile state vcpu pointer array allocated using the (2) XENOPROFgetbuffer or (3) XENOPROFsetpassive hypercall.

Xen 3.2.x through 4.6.x does not limit the number of printk console messages when logging certain pmu and profiling hypercalls, which allows local guests to cause a denial of service via a sequence of crafted (1) HYPERCALLxenoprofop hypercalls, which are not properly handled in the doxenoprofop function in common/xenoprof.c, or (2) HYPERVISORxenpmuop hypercalls, which are not properly handled in the doxenpmuop function in arch/x86/cpu/vpmu.c.

The modl2entry function in arch/x86/mm.c in Xen 3.4 through 4.6.x does not properly validate level 2 page table entries, which allows local PV guest administrators to gain privileges via a crafted superpage mapping.