infinite loop when cleaning up IRQ vectors

ISSUE DESCRIPTION When moving IRQs between CPUs to distribute the load of IRQ handling, IRQ vectors are dynamically allocated and de-allocated on the relevant CPUs. De-allocation has to happen when certain constraints are met. If these conditions are not met when first checked, the checking CPU m...

x86: Race condition in Xen mapping code

ISSUE DESCRIPTION The Xen code handling the updating of the hypervisor's own pagetables tries to use 2MiB and 1GiB superpages as much as possible to maximize TLB efficiency. Some of the operations for checking and coalescing superpages take non-negligible amount of time; to avoid potential lock...

CVE-2020-25604

An issue was discovered in Xen through 4.14.x. There is a race condition when migrating timers between x86 HVM vCPUs. When migrating timers of x86 HVM guests between its vCPUs, the locking model used allows for a second vCPU of the same guest also operating on the timers to release a lock that it...

CVE-2020-25595

An issue was discovered in Xen through 4.14.x. The PCI passthrough code improperly uses register data. Code paths in Xen's MSI handling have been identified that act on unsanitized values read back from device hardware registers. While devices strictly compliant with PCI specifications shouldn't ...

Denial Of Service (DoS)

Xen is vulnerable to denial of service DoS. Arm guest OS users can cause a hypervisor crash because of a missing alignment check in VCPUOPregistervcpuinfo. The hypercall VCPUOPregistervcpuinfo is used by a guest to register a shared region with the hypervisor. The region will be mapped into Xen...

Design/Logic Flaw

An issue was discovered in Xen through 4.13.x, allowing Intel guest OS users to gain privileges or cause a denial of service because of non-atomic modification of a live EPT PTE. When mapping guest EPT nested paging tables, Xen would in some circumstances use a series of non-atomic bitfield write...

CVE-2020-15564

An issue was discovered in Xen through 4.13.x, allowing Arm guest OS users to cause a hypervisor crash because of a missing alignment check in VCPUOPregistervcpuinfo. The hypercall VCPUOPregistervcpuinfo is used by a guest to register a shared region with the hypervisor. The region will be mapped...

Missing alignment check in VCPUOP_register_vcpu_info

ISSUE DESCRIPTION The hypercall VCPUOPregistervcpuinfo is used by a guest to register a shared region with the hypervisor. The region will be mapped into Xen address space so it can be directly accessed. On Arm, the region is accessed with instructions which require a specific alignment...

PT-2020-5907 · Xen +2 · Xen +2

Name of the Vulnerable Software and Affected Versions: Xen versions through 4.13.x Description: An issue in Xen allows Arm guest OS users to cause a hypervisor crash due to a missing alignment check in the VCPUOP register vcpu info hypercall. This hypercall is used by a guest to register a shared...

Race condition

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to gain host OS privileges by leveraging race conditions in pagetable promotion and demotion operations, because of an incomplete fix for CVE-2019-18421. XSA-299 addressed several critical issues in restartable PV type...

Linear pagetable use / entry miscounts

ISSUE DESCRIPTION "Linear pagetables" is a technique which involves either pointing a pagetable at itself, or to another pagetable of the same or higher level. Xen has limited support for linear pagetables: A page may either point to itself, or point to another pagetable of the same level i.e., L...

CVE-2019-18423

An issue was discovered in Xen through 4.12.x allowing ARM guest OS users to cause a denial of service via a XENMEMaddtophysmap hypercall. p2m-maxmappedgfn is used by the functions p2mresolvetranslationfault and p2mgetentry to sanity check guest physical frame. The rest of the code in the two...

Issues with restartable PV type change operations

ISSUE DESCRIPTION To avoid using shadow pagetables for PV guests, Xen exposes the actual hardware pagetables to the guest. In order to prevent the guest from modifying these page tables directly, Xen keeps track of how pages are used using a type system; pages must be "promoted" before being used...

PT-2019-4885 · Xen +1 · Xen +1

Name of the Vulnerable Software and Affected Versions: Xen versions prior to 4.13 Description: An issue in Xen allows ARM guest OS users to cause a denial of service via a XENMEM add to physmap hypercall. The functions p2m resolve translation fault and p2m get entry use p2m-max mapped gfn to sani...

CVE-2018-12893

An issue was discovered in Xen through 4.10.x. One of the fixes in XSA-260 added some safety checks to help prevent Xen livelocking with debug exceptions. Unfortunately, due to an oversight, at least one of these safety checks can be triggered by a guest. A malicious PV guest can crash Xen, leadi...

CVE-2018-12893

An issue was discovered in Xen through 4.10.x. One of the fixes in XSA-260 added some safety checks to help prevent Xen livelocking with debug exceptions. Unfortunately, due to an oversight, at least one of these safety checks can be triggered by a guest. A malicious PV guest can crash Xen, leadi...

x86: PV guest may crash Xen with XPTI

ISSUE DESCRIPTION The workaround for the Meltdown vulnerability XSA-254 failed to deal with an error code path connecting the INT 80 handling with general exception handling. This results in an unconditional write attempt of the value zero to an address near 2^64, in cases where a PV guest has no...

broken x86 shadow mode refcount overflow check

ISSUE DESCRIPTION Pages being used to run x86 guests in shadow mode are reference counted to track their uses. Unfortunately the overflow check when trying to obtain a new reference used a mask one bit wider than the reference count actually is, rendering the entire check ineffective. IMPACT A...

Xen Hypervisor Infinite Loop Guest-to-Host DoS (XSA-246)

According to its self-reported version number, the Xen hypervisor installed on the remote host is affected by an infinite loop guest-to-host denial of service vulnerability. This issue only affects x86 systems that have 2MiB or 1GiB HAP pages enabled. ARM systems are not affected. x86 PV VMs can...

Unlimited recursion in linear pagetable de-typing

ISSUE DESCRIPTION x86 PV guests are permitted to set up certain forms of what is often called "linear page tables", where pagetables contain references to other pagetables at the same level or higher. Certain restrictions apply in order to fit into Xen's page type handling system. An important...