XENMEM_exchange error handling issues

ISSUE DESCRIPTION Error handling in the operation may involve handing back pages to the domain. This operation may fail when in parallel the domain gets torn down. So far this failure unconditionally resulted in the host being brought down due to an internal error being assumed. This is...

Use after free in QEMU/Xen block unplug protocol

ISSUE DESCRIPTION When unplugging an emulated block device the device was not fully unplugged, meaning a second unplug attempt would attempt to unplug the device a second time using a previously freed pointer. IMPACT An HVM guest which has access to an emulated IDE disk device may be able to...

Guest effectable page reference leak in MMU_MACHPHYS_UPDATE handling

ISSUE DESCRIPTION An error handling path in the processing of MMUMACHPHYSUPDATE failed to drop a page reference which was acquired in an earlier processing step. IMPACT Malicious or buggy stub domain kernels or tool stacks otherwise living outside of Domain0 can mount a denial of service attack...

Hardware features unintentionally exposed to guests on ARM

ISSUE DESCRIPTION When running on an ARM platform Xen was not correctly configuring the hardware virtualisation platform and therefore did not prevent guests from accessing various hardware features including cache control, coprocessors, debug registers and various processor specific registers...

x86 pv guest kernel DoS via SYSENTER

ISSUE DESCRIPTION The SYSENTER instruction leaves various state sanitization activities to software. One of Xen's sanitization paths injects a GP fault, and incorrectly delivers it twice to the guest. This causes the guest kernel to observe a kernel-privilege GP fault typically fatal rather than ...

inverted code paths in x86 dirty VRAM tracking

ISSUE DESCRIPTION An inverted conditional in x86 HVM guests' dirty video RAM tracking code allows such guests to make Xen de-reference a pointer guaranteed to point at unmapped space. IMPACT A malicious or buggy HVM guest may cause the hypervisor to crash, resulting in Denial of Service DoS...

x86 HVM: Overflow of sh_ctxt->seg_reg[]

ISSUE DESCRIPTION x86 HVM guests running with shadow paging use a subset of the x86 emulator to handle the guest writing to its own pagetables. There are situations a guest can provoke which result in exceeding the space allocated for internal state. IMPACT A malicious HVM guest administrator can...

Hypervisor heap contents leaked to guests

ISSUE DESCRIPTION While memory pages recovered from dying guests are being cleaned to avoid leaking sensitive information to other guests, memory pages that were in use by the hypervisor and are eligible to be allocated to guests weren't being properly cleaned. Such exposure of information would...

Excessive time to disable caching with HVM guests with PCI passthrough

ISSUE DESCRIPTION HVM guests are able to manipulate their physical address space such that processing a subsequent request by that guest to disable caches takes an extended amount of time changing the cachability of the memory pages assigned to this guest. This applies only when the guest has bee...

x86: TSX Async Abort protections not restored after S3

ISSUE DESCRIPTION This issue relates to the TSX Async Abort speculative security vulnerability. Please see https://xenbits.xen.org/xsa/advisory-305.html for details. Mitigating TAA by disabling TSX the default and preferred option requires selecting a non-default setting in MSRTSXCTRL. This setti...

x86: Mishandling of SYSCALL singlestep during emulation

ISSUE DESCRIPTION The typical behaviour of singlestepping exceptions is determined at the start of the instruction, with a DB trap being raised at the end of the instruction. SYSCALL and SYSRET, although we don't implement it behave differently because the typical behaviour allows userspace to...

qemu ioport array overflow

ISSUE DESCRIPTION The code in qemu which implements ioport read/write looks up the specified ioport address in a dispatch table. The argument to the dispatch function is a uint32t, and is used without a range check, even though the table has entries for only 2^16 ioports. When qemu is used as a...

arm: Host crash caused by VMID exhaustion

ISSUE DESCRIPTION VMIDs are a finite hardware resource, and allocated as part of domain creation. If no free VMIDs are available when trying to create a new domain, a bug in the error path causes a NULL pointer to be used, resulting in a Data Abort and host crash. IMPACT Attempting to create too...

Unrestricted qemu logging

ISSUE DESCRIPTION When the libxl toolstack launches qemu for HVM guests, it pipes the output of stderr to a file in /var/log/xen. This output is not rate-limited in any way. The guest can easily cause qemu to print messages to stderr, causing this file to become arbitrarily large. IMPACT The disk...

Insufficient restrictions on certain MMU update hypercalls

ISSUE DESCRIPTION MMU update operations targeting page tables are intended to be used on PV guests only. The lack of a respective check made it possible for such operations to access certain function pointers which remain NULL when the target guest is using Hardware Assisted Paging HAP. IMPACT...

Flaws in handling traps from 32-bit userspace on 64-bit ARM

ISSUE DESCRIPTION When handling a trap from guest mode on ARM, Xen asserts that the current guest mode must match the domain address width. This assertion is false when a guest takes a trap from a 32-bit userspace running on a 64-bit kernel in a 64-bit domain. IMPACT Any user in a guest which is...

integer overflow in several XSM/Flask hypercalls

ISSUE DESCRIPTION The FLASKGET,SETBOOL, FLASKUSER and FLASKCONTEXTTOSID suboperations of the flask hypercall are vulnerable to an integer overflow on the input size. The hypercalls attempt to allocate a buffer which is 1 larger than this size and is therefore vulnerable to integer overflow and an...

x86/HVM pinned cache attributes mis-handling

ISSUE DESCRIPTION To allow cachability control for HVM guests with passed through devices, an interface exists to explicitly override defaults which would otherwise be put in place. While not exposed to the affected guests themselves, the interface specifically exists for domains controlling such...

inadequate grant-v2 status frames array bounds check

ISSUE DESCRIPTION The v2 grant table interface separates grant attributes from grant status. That is, when operating in this mode, a guest has two tables. As a result, guests also need to be able to retrieve the addresses that the new status tracking table can be accessed through. For 32-bit gues...

NULL pointer deref in event channel poll

ISSUE DESCRIPTION When polling event channels, in general arbitrary port numbers can be specified. Specifically, there is no requirement that a polled event channel ports has ever been created. When the code was generalised from an earlier implementation, introducing some intermediate pointers, a...

Insufficient TLB flushing in VT-d (iommu) code

ISSUE DESCRIPTION An inverted boolean parameter resulted in TLB flushes not happening upon clearing of a present translation table entry. Retaining stale TLB entries could allow guests access to memory that ought to have been revoked, or grant greater access than intended. IMPACT Malicious guest...

x86 HVM hypercalls may trigger Xen bug check

ISSUE DESCRIPTION Unlike 32-bit PV guests, HVM guests may switch freely between 64-bit and other modes. This in particular means that they may set registers used to pass 32-bit-mode hypercall arguments to values outside of the range 32-bit code would be able to set them to. When processing of...

IOMMU page mapping issues on x86

ISSUE DESCRIPTION Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply ...

x86 software interrupt injection mis-handled

ISSUE DESCRIPTION There are two closely-related bugs. When Xen emulates instructions which generate software interrupts it needs to perform a privilege check involving an IDT lookup. This check is sometimes erroneously conducted as if the IDT had the format for a 32-bit guest, when in fact it is ...

Off-by-one error in FLASK_AVC_CACHESTAT hypercall

ISSUE DESCRIPTION The FLASKAVCCACHESTAT hypercall, which provides access to per-cpu statistics on the Flask security policy, incorrectly validates the CPU for which statistics are being requested. IMPACT An attacker can cause the hypervisor to read past the end of an array. This may result in...

Multiple vulnerabilities in libelf PV kernel handling

ISSUE DESCRIPTION The ELF parser used by the Xen tools to read domains' kernels and construct domains has multiple integer overflows, pointer dereferences based on calculations from unchecked input values, and other problems. This corresponds to the following CVEs: CVE-2013-2194 XEN XSA-55 intege...

x86/AMD: Zenbleed

ISSUE DESCRIPTION Researchers at Google have discovered Zenbleed, a hardware bug causing corruption of the vector registers. When a VZEROUPPER instruction is discarded as part of a bad transient execution path, its effect on internal tracking are not unwound correctly. This manifests as the wrong...

Guests can trigger deadlock in Linux netback driver

ISSUE DESCRIPTION The patch for XSA-392 introduced another issue which might result in a deadlock when trying to free the SKB of a packet dropped due to the XSA-392 handling CVE-2022-42328. Additionally when dropping packages for other reasons the same deadlock could occur in case of netpoll bein...

x86 pv: Race condition in typeref acquisition

ISSUE DESCRIPTION Xen maintains a type reference count for pages, in addition to a regular reference count. This scheme is used to maintain invariants required for Xen's safety, e.g. PV guests may not have direct writeable access to pagetables; updates need auditing by Xen. Unfortunately, the log...

xen/arm: No memory limit for dom0less domUs

ISSUE DESCRIPTION The dom0less feature allows an administrator to create multiple unprivileged domains directly from Xen. Unfortunately, the memory limit from them is not set. This allow a domain to allocate memory beyond what an administrator originally configured. IMPACT Malicious dom0less gues...

oxenstored: permissions not checked on root node

ISSUE DESCRIPTION In the Ocaml xenstored implementation, the internal representation of the tree has special cases for the root node, because this node has no parent. Unfortunately, permissions were not checked for certain operations on the root node. Unprivileged guests can get and modify...

qemu incautious about shared ring processing

ISSUE DESCRIPTION The compiler can emit optimizations in qemu which can lead to double fetch vulnerabilities. Specifically data on the rings shared between qemu and the hypervisor which the guest under control can obtain mappings of can be fetched twice during which time the guest can alter the...

x86: unintentional logging upon guest changing callback method

ISSUE DESCRIPTION HYPERVISORhvmop sub-op HVMOPsetparam's HVMPARAMCALLBACKIRQ operation intends to log the new callback method in debug builds only. The full message, however, is split into two parts, the second one of which didn't get suppressed on non-debug builds as would have been intended...

Long latency virtual-mmu operations are not preemptible

ISSUE DESCRIPTION Some MMU virtualization operations on HVM guests must process every page assigned to a guest. For larger guests, this can tie up a vcpu for a significant amount of time, as the operations are not preemptible. For guests using Hardware Assisted Paging HAP, see below this is...

VT-d: Failure to quarantine devices in !HVM builds

ISSUE DESCRIPTION Incorrect placement of a preprocessor directive in source code results in logic that doesn't operate as intended when support for HVM guests is compiled out of Xen. IMPACT When a device is removed from a domain, it is not properly quarantined and retains its access to the domain...

x86: speculative vulnerability in 32bit SYSCALL path

ISSUE DESCRIPTION Due to an oversight in the very original Spectre/Meltdown security work XSA-254, one entrypath performs its speculation-safety actions too late. In some configurations, there is an unprotected RET instruction which can be attacked with a variety of speculative attacks. IMPACT An...

undue recursion in x86 HVM context switch code

ISSUE DESCRIPTION When they require assistance from the device model, x86 HVM guests must be temporarily de-scheduled. The device model will signal Xen when it has completed its operation, via an event channel, so that the relevant vCPU is rescheduled. If the device model were to signal Xen witho...

XAPI: guest-triggered excessive memory usage

ISSUE DESCRIPTION Certain xenstore keys provide feedback from the guest, and are therefore watched by toolstack. Specifically, keys are watched by xenopsd, and data are forward via RPC through message-switch to xapi. The watching logic in xenopsd sends one RPC update containing all data, any time...

stack corruption from XSA-346 change

ISSUE DESCRIPTION One of the two changes for XSA-346 introduced an on-stack array. The check for guarding against overrunning this array was off by one, allowing for corruption of the first stack slot immediately following this array. IMPACT A malicious or buggy HVM or PVH guest can cause Xen to...

Linux ioperm bitmap context switching issues

ISSUE DESCRIPTION Linux 5.5 overhauled the internal state handling for the iopl and ioperm system calls. Unfortunately, one aspect on context switch wasn't wired up correctly for the Xen PVOps case. IMPACT IO port permissions don't get rescinded when context switching to an unprivileged task...

libvchan failure handling malicious ring indexes

ISSUE DESCRIPTION libvchan a library for inter-domain communication does not correctly handle unusual or malicious contents in the xenstore ring. A malicious guest can exploit this to cause a libvchan-using facility to read or write past the end of the ring. IMPACT libvchan-using facilities are...

Buffer overflow in xencontrol Python bindings affecting xend

ISSUE DESCRIPTION The Python bindings for the xcvcpusetaffinity call do not properly check their inputs. Systems which allow untrusted administrators to configure guest vcpu affinity may be exploited to trigger a buffer overrun and corrupt memory. IMPACT An attacker who is able to configure a...

xen/arm: Boot modules are not scrubbed

ISSUE DESCRIPTION The bootloader will load boot modules e.g. kernel, initramfs... in a temporary area before they are copied by Xen to each domain memory. To ensure sensitive data is not leaked from the modules, Xen must "scrub" them before handing the page over to the allocator. Unfortunately, i...

FIFO event channels control structure ordering

ISSUE DESCRIPTION A bounds check common to most operation time functions specific to FIFO event channels depends on the CPU observing consistent state. While the producer side uses appropriately ordered writes, the consumer side isn't protected against re-ordered reads, and may hence end up...

x86: Mishandling of instruction pointer truncation during emulation

ISSUE DESCRIPTION When emulating HVM instructions, Xen uses a small i-cache for fetches from guest memory. The code that handles cache misses does not check if the address from which it fetched lies within the cache before blindly writing to it. As such it is possible for the guest to overwrite...

libxl leak of pv kernel and initrd on error

ISSUE DESCRIPTION When constructing a guest which is configured to use a PV bootloader which runs as a userspace process in the toolstack domain e.g. pygrub libxl creates a mapping of the files to be used as kernel and initial ramdisk when building the guest domain. However if building the domain...

GNTTABOP_swap_grant_ref operation misbehavior

ISSUE DESCRIPTION With the introduction of version 2 grant table operations, a version check became necessary for most grant table related hypercalls. The GNTTABOPswapgrantref call was lacking such a check. As a result, the subsequent code behaved as if version 2 was in use, when a guest issued...

several hypercalls do not validate input GFNs

ISSUE DESCRIPTION The function getpagefromgfn does not validate its input GFN. An invalid GFN passed to a hypercall which uses this function will cause the hypervisor to read off the end of the frame table and potentially crash. IMPACT A malicious guest administrator of a PV guest can cause Xen t...

x86 shadow plus log-dirty mode use-after-free

ISSUE DESCRIPTION In environments where host assisted address translation is necessary but Hardware Assisted Paging HAP is unavailable, Xen will run guests in so called shadow mode. Shadow mode maintains a pool of memory used for both shadow page tables as well as auxiliary data structures. To...

Xenstore: new domains inheriting existing node permissions

ISSUE DESCRIPTION Access rights of Xenstore nodes are per domid. Unfortunately, existing granted access rights are not removed when a domain is destroyed. This means that a new domain created with the same domid will inherit the access rights to Xenstore nodes from the previous domains with the...