double unlock in x86 guest IRQ handling

ISSUE DESCRIPTION An optional feature of PCI MSI called "Multiple Message" allows a device to use multiple consecutive interrupt vectors. Unlike for MSI-X, the setting up of these consecutive vectors needs to happen all in one go. In this handling an error path could be taken in different...

Linux/xen-netfront: Memory leak due to missing cleanup function

ISSUE DESCRIPTION In netfront, xennetalloconerxbuffer failed to call the appropriate clean-up function, resulting in a memory leak. IMPACT A malicious guest userspace process can exhaust memory resources within the guest kernel, potentially leading to a guest crash Denial of Service. It is not...

x86: Incorrect logic for BTC/SRSO mitigations

ISSUE DESCRIPTION Because of a logical error in XSA-407 Branch Type Confusion, the mitigation is not applied properly when it is intended to be used. XSA-434 Speculative Return Stack Overflow uses the same infrastructure, so is equally impacted. For more details, see:...

x86: Native Branch History Injection

ISSUE DESCRIPTION In August 2022, researchers at VU Amsterdam disclosed Spectre-BHB. Spectre-BHB was discussed in XSA-398. At the time, the susceptibility of Xen to Spectre-BHB was uncertain so no specific action was taken in XSA-398. However, various changes were made thereafter in upstream Xen ...

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...

x86: Register File Data Sampling

ISSUE DESCRIPTION Intel have disclosed RFDS, Register File Data Sampling, affecting some Atom cores. This came from internal validation work. There is no information provided about how an attacker might go about inferring data from the register files. For more details, see:...

GhostRace: Speculative Race Conditions

ISSUE DESCRIPTION Researchers at VU Amsterdam and IBM Research have discovered GhostRace; an analysis of the behaviour of synchronisation primitives under speculative execution. Synchronisation primitives are typically formed as an unbounded loop which waits until a resource is available to be...

x86: shadow stack vs exceptions from emulation stubs

ISSUE DESCRIPTION Recent x86 CPUs offer functionality named Control-flow Enforcement Technology CET. A sub-feature of this are Shadow Stacks CET-SS. CET-SS is a hardware feature designed to protect against Return Oriented Programming attacks. When enabled, traditional stacks holding both data and...

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...

pci: phantom functions assigned to incorrect contexts

ISSUE DESCRIPTION PCI devices can make use of a functionality called phantom functions, that when enabled allows the device to generate requests using the IDs of functions that are otherwise unpopulated. This allows a device to extend the number of outstanding requests. Such phantom functions nee...

Linux: netback processing of zero-length transmit fragment

ISSUE DESCRIPTION Transmit requests in Xen's virtual network protocol can consist of multiple parts. While not really useful, except for the initial part any of them may be of zero length, i.e. carry no data at all. Besides a certain initial portion of the to be transferred data, these parts are...

arm32: The cache may not be properly cleaned/invalidated (take two)

ISSUE DESCRIPTION Arm provides multiple helpers to clean & invalidate the cache for a given region. This is, for instance, used when allocating guest memory to ensure any writes such as the ones during scrubbing have reached memory before handing over the page to a guest. Unfortunately, the...

x86/AMD: mismatch in IOMMU quarantine page table levels

ISSUE DESCRIPTION The current setup of the quarantine page tables assumes that the quarantine domain domio has been initialized with an address width of DEFAULTDOMAINADDRESSWIDTH 48 and hence 4 page table levels. However domio being a PV domain gets the AMD-Vi IOMMU page tables levels based on th...

x86: BTC/SRSO fixes not fully effective

ISSUE DESCRIPTION The fixes for XSA-422 Branch Type Confusion and XSA-434 Speculative Return Stack Overflow are not IRQ-safe. It was believed that the mitigations always operated in contexts with IRQs disabled. However, the original XSA-254 fix for Meltdown XPTI deliberately left interrupts enabl...

x86/AMD: Debug Mask handling

ISSUE DESCRIPTION AMD CPUs since 2014 have extensions to normal x86 debugging functionality. Xen supports guests using these extensions. Unfortunately there are errors in Xen's handling of the guest state, leading to denials of service. 1 CVE-2023-34327 - An HVM vCPU can end up operating in the...

Possible deadlock in Linux kernel event handling

ISSUE DESCRIPTION Closing of an event channel in the Linux kernel can result in a deadlock. This happens when the close is being performed in parallel to an unrelated Xen console action and the handling of a Xen console interrupt in an unprivileged guest. The closing of an event channel is e.g...

xenstored: A transaction conflict can crash C Xenstored

ISSUE DESCRIPTION When a transaction is committed, C Xenstored will first check the quota is correct before attempting to commit any nodes. It would be possible that accounting is temporarily negative if a node has been removed outside of the transaction. Unfortunately, some versions of C Xenstor...

Multiple vulnerabilities in libfsimage disk handling

ISSUE DESCRIPTION libfsimage contains parsing code for several filesystems, most of them based on grub-legacy code. libfsimage is used by pygrub to inspect guest disks. Pygrub runs as the same user as the toolstack root in a priviledged domain. At least one issue has been reported to the Xen...

x86/AMD: missing IOMMU TLB flushing

ISSUE DESCRIPTION The caching invalidation guidelines from the AMD-Vi specification 48882—Rev 3.07-PUB—Oct 2022 is incorrect on some hardware, as devices will malfunction see stale DMA mappings if some fields of the DTE are updated but the IOMMU TLB is not flushed. Such stale DMA mappings can poi...

x86/AMD: Divide speculative information leak

ISSUE DESCRIPTION In the Zen1 microarchitecure, there is one divider in the pipeline which services uops from both threads. In the case of DE, the latched result from the previous DIV to execute will be forwarded speculatively. This is a covert channel that allows two threads to communicate witho...

top-level shadow reference dropped too early for 64-bit PV guests

ISSUE DESCRIPTION For migration as well as to work around kernels unaware of L1TF see XSA-273, PV guests may be run in shadow paging mode. Since Xen itself needs to be mapped when PV guests run, Xen and shadowed PV guests run directly the respective shadow page tables. For 64-bit PV guests this...

arm32: The cache may not be properly cleaned/invalidated

ISSUE DESCRIPTION Arm provides multiple helpers to clean & invalidate the cache for a given region. This is, for instance, used when allocating guest memory to ensure any writes such as the ones during scrubbing have reached memory before handing over the page to a guest. Unfortunately, the...

x86/AMD: Speculative Return Stack Overflow

ISSUE DESCRIPTION Researchers from ETH Zurich have extended their prior research XSA-422, Branch Type Confusion, a.k.a Retbleed and have discovered INCEPTION, also know as RAS Return Address Stack Poisoning, and Speculative Return Stack Overflow. The RAS is updated when a CALL instruction is...

Linux: buffer overrun in netback due to unusual packet

ISSUE DESCRIPTION The fix for XSA-423 added logic to Linux'es netback driver to deal with a frontend splitting a packet in a way such that not all of the headers would come in one piece. Unfortunately the logic introduced there didn't account for the extreme case of the entire packet being split...

x86/Intel: Gather Data Sampling

ISSUE DESCRIPTION A researcher has discovered Gather Data Sampling, a transient execution side-channel whereby the AVX GATHER instructions can forward the content of stale vector registers to dependent instructions. The physical register file is a structure competitively shared between sibling...

arm: Guests can trigger a deadlock on Cortex-A77

ISSUE DESCRIPTION Cortex-A77 cores r0p0 and r1p0 are affected by erratum 1508412 where software, under certain circumstances, could deadlock a core due to the execution of either a load to device or non-cacheable memory, and either a store exclusive or register read of the Physical Address Regist...

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...

Mishandling of guest SSBD selection on AMD hardware

ISSUE DESCRIPTION The current logic to set SSBD on AMD Family 17h and Hygon Family 18h processors requires that the setting of SSBD is coordinated at a core level, as the setting is shared between threads. Logic was introduced to keep track of how many threads require SSBD active in order to...

x86 shadow paging arbitrary pointer dereference

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. Due to too lax a check in one of the hypervisor routines used for shadow page handling it is possible for a guest...

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...

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...

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...

x86: Cross-Thread Return Address Predictions

ISSUE DESCRIPTION It has been discovered that on some AMD CPUs, the RAS Return Address Stack, also called RAP - Return Address Predictor - in some AMD documentation, and RSB - Return Stack Buffer - in Intel terminology is dynamically partitioned between non-idle threads. This allows an attacker t...

Guests can cause Xenstore crash via soft reset

ISSUE DESCRIPTION When a guest issues a "Soft Reset" e.g. for performing a kexec the libxl based Xen toolstack will normally perform a XSRELEASE Xenstore operation. Due to a bug in xenstored this can result in a crash of xenstored. Any other use of XSRELEASE will have the same impact. IMPACT A...

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...

Guests can trigger NIC interface reset/abort/crash via netback

ISSUE DESCRIPTION It is possible for a guest to trigger a NIC interface reset/abort/crash in a Linux based network backend by sending certain kinds of packets. It appears to be an unwritten? assumption in the rest of the Linux network stack that packet protocol headers are all contained within th...

x86: Multiple speculative security issues

ISSUE DESCRIPTION 1 Researchers have discovered that on some AMD CPUs, the implementation of IBPB Indirect Branch Prediction Barrier does not behave according to the specification. Specifically, IBPB fails to properly flush the RAS Return Address Stack, also RSB - Return Stack Buffer - in Intel...

Oxenstored 32->31 bit integer truncation issues

ISSUE DESCRIPTION Integers in Ocaml are 63 or 31 bits of signed precision. The Ocaml Xenbus library takes a C uint32t out of the ring and casts it directly to an Ocaml integer. In 64-bit Ocaml builds this is fine, but in 32-bit builds, it truncates off the most significant bit, and then creates...

Xenstore: Cooperating guests can create arbitrary numbers of nodes

ISSUE DESCRIPTION Since the fix of XSA-322 any Xenstore node owned by a removed domain will be modified to be owned by Dom0. This will allow two malicious guests working together to create an arbitrary number of Xenstore nodes. This is possible by domain A letting domain B write into domain A's...

Xenstore: Guests can get access to Xenstore nodes of deleted domains

ISSUE DESCRIPTION Access rights of Xenstore nodes are per domid. When a domain is gone, there might be Xenstore nodes left with access rights containing the domid of the removed domain. This is normally no problem, as those access right entries will be corrected when such a node is written later...

x86: unintended memory sharing between guests

ISSUE DESCRIPTION On Intel systems that support the "virtualize APIC accesses" feature, a guest can read and write the global shared xAPIC page by moving the local APIC out of xAPIC mode. Access to this shared page bypasses the expected isolation that should exist between two guests. IMPACT Guest...

Xenstore: Guests can crash xenstored via exhausting the stack

ISSUE DESCRIPTION Xenstored is using recursion for some Xenstore operations e.g. for deleting a sub-tree of Xenstore nodes. With sufficiently deep nesting levels this can result in stack exhaustion on xenstored, leading to a crash of xenstored. IMPACT A malicious guest creating very deep nesting...

Xenstore: Guests can create orphaned Xenstore nodes

ISSUE DESCRIPTION By creating multiple nodes inside a transaction resulting in an error, a malicious guest can create orphaned nodes in the Xenstore data base, as the cleanup after the error will not remove all nodes already created. When the transaction is committed after this situation, nodes...

Xenstore: Guests can create arbitrary number of nodes via transactions

ISSUE DESCRIPTION In case a node has been created in a transaction and it is later deleted in the same transaction, the transaction will be terminated with an error. As this error is encountered only when handling the deleted node at transaction finalization, the transaction will have been...

Xenstore: Guests can cause Xenstore to not free temporary memory

ISSUE DESCRIPTION When working on a request of a guest, xenstored might need to allocate quite large amounts of memory temporarily. This memory is freed only after the request has been finished completely. A request is regarded to be finished only after the guest has read the response message of...

Xenstore: Guests can crash xenstored

ISSUE DESCRIPTION Due to a bug in the fix of XSA-115 a malicious guest can cause xenstored to use a wrong pointer during node creation in an error path, resulting in a crash of xenstored or a memory corruption in xenstored causing further damage. Entering the error path can be controlled by the...

Xenstore: guests can let run xenstored out of memory

ISSUE DESCRIPTION Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service DoS of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the...

P2M pool freeing may take excessively long

ISSUE DESCRIPTION The P2M pool backing second level address translation for guests may be of significant size. Therefore its freeing may take more time than is reasonable without intermediate preemption checks. Such checking for the need to preempt was so far missing. IMPACT A group of...

Arm: unbounded memory consumption for 2nd-level page tables

ISSUE DESCRIPTION Certain actions require e.g. removing pages from a guest's P2M Physical-to-Machine mapping. When large pages are in use to map guest pages in the 2nd-stage page tables, such a removal operation may incur a memory allocation to replace a large mapping with individual smaller ones...

XAPI open file limit DoS

ISSUE DESCRIPTION It is possible for an unauthenticated client on the network to cause XAPI to hit its file-descriptor limit. This causes XAPI to be unable to accept new requests for other trusted clients, and blocks XAPI from carrying out any tasks that require the opening of file descriptors...