bleader

Update published: https://xcp-ng.org/blog/2024/09/27/september-2024-security-updates/

Thank you for the tests!

New security update candidates (xen)

Two new XSAs were published on 30th of January.

• XSA-449 impacts PCI passthrough users.
• XSA-450 is only impacting the case where Xen is compiled without HVM support, that is not the case in XCP-ng. We therefore chose not to include this fix yet (will likely be included in future versions, maybe not part of a critical security update).

SECURITY UPDATES

• xen-*:
      * Fix XSA-449 - pci: phantom functions assigned to incorrect contexts. A malicious VM assigned with a PCI device could in some cases access data of a guest previously using the same PCI device. This requires PCI passthrough on a device using phantom functions and reassigning the same device to a new VM to be exploitable.

Test on XCP-ng 8.2

yum clean metadata --enablerepo=xcp-ng-testing
yum update "xen-*" --enablerepo=xcp-ng-testing
reboot

The usual update rules apply: pool coordinator first, etc.

Versions:

• xen: 4.13.5-9.38.2.xcpng8.2

What to test

Normal use and anything else you want to test, if you are using PCI passthrough devices that's even better, but we also would be glad to have confirmation from others that their normal use case still works as intended.

Test window before official release of the updates
2 day because of security updates.

New security update candidates (kernel)

A new XSA was published on the 23rd of January, so we have a new security update to include it.

Security updates

• kernel:
    * Fix XSA-448 - Linux: netback processing of zero-length transmit fragment. An unprivileged guest can cause Denial of Service (DoS) of the host bysending network packets to the backend, causing the backend to crash. This was discovered through issues when using pfSense with wireguard causing random crashes of the host.

Test on XCP-ng 8.2

yum clean metadata --enablerepo=xcp-ng-testing
yum update kernel --enablerepo=xcp-ng-testing
reboot

The usual update rules apply: pool coordinator first, etc.

Versions:

• kernel: 4.19.19-7.0.23.1.xcpng8.2

What to test

Normal use and anything else you want to test. The closer to your actual use of XCP-ng, the better.

Test window before official release of the updates
~2 days due to security updates.

Update published: https://xcp-ng.org/blog/2025/05/14/may-2025-security-update-for-xcp-ng-8-2-8-3/

Thank your for the tests.

Update published https://xcp-ng.org/blog/2024/07/18/july-2024-security-updates/

Thank you everyone for your tests!

New security update candidate (xen, xapi, xsconsole)

Two new XSAs were published on 16th of July.

---

• XSA-458 guests which have a multi-vector MSI capable device passed through to them can leverage the vulnerability.
• XSA-459 impacts systems running Xapi v3.249.x, which means any up to date XCP-ng 8.2. Note this requires heavy crafting and likely social engineering on the attacker side, see the XSA's "VULNERABLE SYSTEMS" section for more details.

---

SECURITY UPDATES

• xen-*:
  • Fix XSA-458 - double unlock in x86 guest IRQ handling. When passing through a multi-vector MSI capable device to a guest, an attacker could use an error handling path that could lead to the issue, no exploitations results have been ruled out: Denial of Service (DoS), crashes, information leaks, or elevation of privilege could all be possible.
• xapi, xsconsole:
  • Fix XSA-459 - Xapi: Metadata injection attack against backup/restore functionality. A malicious guest can manipulate its disk to appear to be a metadata
    backup, then having about a 50% chance of appearing ahead of a legitimate metadata backup. The more disks the guest has, the higher the chances of this happening are.

Test on XCP-ng 8.2

yum clean metadata --enablerepo=xcp-ng-testing
yum update "xen-*" "xapi-*" xsconsole --enablerepo=xcp-ng-testing
reboot

The usual update rules apply: pool coordinator first, etc.

Versions:

• xen: xen-4.13.5-9.40.2.xcpng8.2
• xapi: xapi-1.249.36-1.2.xcpng8.2
• xsconsole: xsconsole-10.1.13-1.2.xcpng8.2

What to test

Normal use and anything else you want to test.

Test window before official release of the update

~ 1 day because of security updates.

The update has been published, thanks for testing.

https://xcp-ng.org/blog/2024/02/02/february-2024-security-update/

The update has been published, thanks for the feedback and tests.

https://xcp-ng.org/blog/2024/01/26/january-2024-security-update/

Hello guys,

I'll be the one investigating this further, we're trying to compile a list of CPUs and their behavior. First, thank you for your reports and tests, that's already very helpful and gave us some insight already.

Setup

If some of you can help us cover more ground that would be awesome, so here is what would be an ideal for testing to get everyone on the same page:

• An AMD host, obviously
  • yum install iperf ²
• 2 VMs on the same host, with the distribution of your choice¹
  • each with 4 cores if possible
  • 1GB of ram should be enough if you don't have a desktop environment to load
  • iperf2²

¹: it seems some recent kernels do provide a slight boost, but in any case the performance is pretty low for such high grade CPUs.
²: iperf3 is singlethreaded, the -P option will establish multiple connexions, but it will process all of them in a single thread, so if reaching a 100% cpu usage, it won't get much increase and won't help identifying the scaling on such a cpu. For example on a Ryzen 5 7600 processor, we do have about the same low perfomances, but using multiple thread will scale, which does not seem to be the case for EPYC Zen1 CPUs.

Tests

• do not disable mitigations for now, as its only on kernel side, there are still mitigation active in xen, and from my testing it doesn't seem to help much, and will increase combinatory of results
• for each test, run xentop on host, and try to get an idea of the top values of each domain when the test is running
• run iperf -s on VM1, and let it run (no -P X this would stop after X connexion established)
• tests:
  • vm2vm 1 thread: on VM2, run iperf -c <ip_VM1> -t 60, note result for v2v 1 thread
  • vm2vm 4 threads on VM2, run iperf -c <ip_VM1> -t 60 -P4, note result for v2v 4 threads
  • host2vm 1 thread: on host, run iperf -c <ip_VM1> -t 60, note result for h2v 1 thread
  • host2vm 4 threads on host, run iperf -c <ip_VM1> -t 60 -P4, note result for h2v 4 threads

Report template

Here is an example of report template

• Host:
  • cpu:
  • number of sockets:
  • cpu pinning: yes (detail) / no (use automated setting)
  • xcp-ng version:
  • output of xl info -n especially the cpu_topology section in a code block.
• VMs:
  • distrib & version
  • kernel version
• Results:
  • v2m 1 thread: throughput / cpu usage from xentop³
  • v2m 4 threads: throughput / cpu usage from xentop³
  • h2m 1 thread: througput / cpu usage from xentop³
  • h2m 4 threads: througput / cpu usage from xentop³

³: I note the max I see while test is running in vm-client/vm-server/host order.

What was tested

Mostly for information, here are a few tests I ran which did not seem to improve performances.

• disabling the mitigations of various security issues at host and VM boot time using kernel boot parameters: noibrs noibpb nopti nospectre_v2 spectre_v2_user=off spectre_v2=off nospectre_v1 l1tf=off nospec_store_bypass_disable no_stf_barrier mds=off mitigations=off. Note this won't disable them at xen level as there are patches that enable the fixes for the related hardware with no flags to disable them.
• disabling AVX passing noxsave in kernel boot parameters as there is a known issue on Zen CPU avoided boosting when a core is under heavy AVX load, still no changes.
• Pinning: I tried to use a single "node" in case the memory controllers are separated, I tried avoiding the "threads" on the same core, and I tried to spread load accross nodes, althrough it seems to give a sllight boost, it still is far from what we should be expecting from such CPUs.
• XCP-ng 8.2 and 8.3-beta1, seems like 8.3 is a tiny bit faster, but tends to jitter a bit more, so I would not deem that as relevant either.

Not tested it myself but @nicols tried on the same machine giving him about 3Gbps as we all see, on VMWare, and it went to ~25Gbps single threaded and about 40Gbps with 4 threads, and with proxmox about 21.7Gbps (I assume single threaded) which are both a lot more along what I would expect this hardware to produce.

@JamesG did test windows and debian guests and got about the same results.

Althrough we do get a small boost by increasing threads (or connexions in case of iperf3), it still is far from what we can see on other setups with vmware or proxmox).

Althrough Olivier's pool with zen4 desktop cpu do scale a lot better than EPYCs when increasing the number of threads, it still is not providing us with expected results for such powerful cpus in single thread (we do not even reach vmware single thread performances with 4 threads).

Althrough @Ajmind-0 test show a difference between debian versions, results even on debian 11 are stil not on par with expected results.

Disabling AVX only provided an improvement on my home FX cpu, which are known to not have real "threads" and share computing unit between 2 threads of a core, so it does make sense. (this is not shown in the table)

It seems that memcpy in the glibc is not related to the issue, dd if=/dev/zero of=/dev/null has decent performances on these machines (1.2-1.3GBytes/s), and it's worth keeping in mind that both kernel and xen have their own implementation, so it could play a small role in filling the ring buffer in iperf, but I feel like the libc memcpy() is not at play here.

Tests table

I'll update this table with updated results, or maybe repost it in further post.

Throughputs are in Gbit/s, noted as G for shorter table entries.

CPU usages are for (VMclient/VMserver/dom0) in percentage as shown in xentop.

user	cpu	family	market	v2v 1T	v2v 4T	h2v 1T	h2v 4T	notes
vates	fx8320-e	piledriver	desktop	5.64 G (120/150/220)	7.5 G (180/230/330)	9.5 G (0/110/160)	13.6 G (0/300/350)	not a zen cpu, no boost
vates	EPYC 7451	Zen1	server	4.6 G (110/180/250)	6.08 G (180/220/300)	7.73 G (0/150/230)	11.2 G (0/320/350)	no boost
vates	Ryzen 5 7600	Zen4	desktop	9.74 G (70/80/100)	19.7 G (190/260/300)	19.2G (0/110/140)	33.9 G (0/310/350)	Olivier's pool, no boost
nicols	EPYC 7443	Zen3	server	3.38 G (?)				iperf3
nicols	EPYC 7443	Zen3	server	2.78 G (?)	4.44 G (?)			iperf2
nicols	EPYC 7502	Zen2	server	similar ^	similar ^			iperf2
JamesG	EPYC 7302p	Zen2	server		6.58 G (?)			iperf3
Ajmind-0	EPYC 7313P	Zen3	server	7.6 G (?)	10.3 G (?)			iperf3, debian11
Ajmind-0	EPYC 7313P	Zen3	server	4.4 G (?)	3.07G (?)			iperf3, debian12
vates	EPYC 9124	Zen4	server	1.16 G (16/17/??⁴)	1.35 G (20/25/??⁴)	N/A	N/A	!xcp-ng, Xen 4.18-rc + suse 15
vates	EPYC 9124	Zen4	server	5.70 G (100/140/200)	10.4 G (230/250/420)	10.7 G (0/120/200)	15.8 G (0/320/380)	no boost
vates	Ryzen 9 5950x	Zen3	desktop	7.25 G (30/35/60)	16.5 G (160/210/300)	17.5 G (0/110/140)	27.6 G (0/270/330)	no boost

⁴: xentop on this host shows 3200% on dom0 all the time, profiling does not seem to show anything actually using CPU, but may be related to the extremely poor performance

last updated: 2023-11-29 16:46

All help is welcome! For those of you who already provided tests I integrated in the table, feel free to not rerun tests, it looks like following the exact protocol and provided more data won't make much of a difference and I don't want to waste your time!

Thanks again to all of you for your insight and your patience, it looks like this is going to be a deep rabbit hole, I'll do my best to get to the bottom of this as soon as possible.

So, after our investigations, we were able to pinpoint the issue.

It seem to happen on most RHEL derivative distributions when migrating from 8.7 to 8.8. As suggested, the bug is in the kernel.

Starting with 4.18.0-466.el8 the patch: x86/idt: Annotate alloc_intr_gate() with __init is integrated and will create the issue. It is missing x86/xen: Split HVM vector callback setup and interrupt gate allocation that should have been integrated as well.

The migration to 8.8 will move you to 4.18.0-477.* versions that are also raising this issue, that's what you reported.

We found that the 4.18.0-488 that can be found in CentOS 8 Stream integrates the missing patch, and do indeed work when installed manually.

Your report helped us identify and reproduce the issues. That allowed us to provide a callstack to Xen devs. Then Roger Pau Monné found that it was this patch missing quickly, and we were able to find which versions of the kernel RPMs were integrating it and when the fix was integrated.

This means the issue was identified on RH side, and it is now a matter of having an updated kernel in derivative distributions like Rocky and Alma.