fuckwit/kaiser/kpti

Idar Lund

Member
Jan 26, 2016
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With the surfacing of the Intel CPU security vulnerability, and recent patches done to the linux kernel.
Sources;
https://en.wikipedia.org/wiki/Kernel_page-table_isolation
http://pythonsweetness.tumblr.com/post/169166980422/the-mysterious-case-of-the-linux-page-table/amp
https://www.theregister.co.uk/2018/01/02/intel_cpu_design_flaw/
According to these, the fix for linux is implemented in 4.15 (rc6) and 14.14.11+. Proxmox is running on 14.13. Will you backport this patch to 14.13 or will you upgrade the kernel to 14.14.11+? And when will you do so?
According to these sorces;
https://twitter.com/never_released/status/947935213010718720
https://twitter.com/jschauma/status/941447173245370368
..both Microsoft and Amazon is urging reboots of virtual hosts in the near future.
I don't want to stress you guys.. but we really need this patch upstream as fast as possible!
 
Last edited:

fabian

Proxmox Staff Member
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Jan 7, 2016
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we are aware of the issue and tracking developments. we will follow Ubuntu's 4.13 backports and release updated kernel packages once those are available.
 

fabian

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Jan 7, 2016
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Is this bug exploitable through a KVM guest using CPU host option?

Will it be a patch for PVE 3.X versions?

not many details are known yet. we will provide patched kernels for 4.4 and 5.1 as soon as final patches are available. 3.4 is EOL, there haven't been any updates for quite a while, and there won't be any updates now either.
 
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alain

Active Member
May 17, 2009
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Hi all,

The application of this kernel security patch could result on noticeable performance impact, notably on servers. See for example this first bechmark from Phoronix :

https://www.phoronix.com/scan.php?page=article&item=linux-415-x86pti&num=1

So I wonder if this patch should be applied mandatory. For exemple, on private virtualization cluster, like mines, it it perhaps not required to apply the patch (perhaps with the linux option nokpti), as security issues would not be very serious in this case, but I would see performance degradation of my cluster ?

Notice that a security patch on Xen, presently under embargo, should be published tomorrow, and it could be related to this flaw (in Intel architecture).
https://xenbits.xen.org/xsa/

But Xen applies patch to the kernel, not KVM.
 

Idar Lund

Member
Jan 26, 2016
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wonder if this patch should be applied mandatory. For exemple, on private virtualization cluster, like mines, it it perhaps not required to apply the patch (perhaps with the linux option nokpti), as security issues would not be very serious in this case, but I would see performance degradation of my cluster ?

It's a kernel patch. It can be disabled with kernel parameter "pti=off" in grub config file.
 

LnxBil

Famous Member
Feb 21, 2015
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For exemple, on private virtualization cluster, like mines, it it perhaps not required to apply the patch (perhaps with the linux option nokpti), as security issues would not be very serious in this case

I cannot imagine anything that runs without some kind of internet interaction nowadays. As long as simply browsing a webpage can exploit this bug, it should be fixed by not deliberately disabling a fix.

Maybe it's time to buy more AMD servers for data centers :-D
 
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speedbird

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Nov 3, 2017
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Any news on when there's going to be an official update released? With all the info surfacing now, it seems to be a massive risk for all of us running VM environments.
 

fabian

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Jan 7, 2016
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there are no final public patches for Meltdown for either kernel 4.4 or 4.13 yet. once there are, we will review and include them ASAP.

Meltdown, which looks to be far more easily exploitable than Spectre, should not be usable from within KVM-enabled VMs to read host kernel memory, but containers are affected. compare the Xen advisory stating that only PV guests are affected by Meltdown (which they call "SP3").

concrete details regarding Spectre are still a bit rare, but AFAICT there are no public general PoCs yet allowing escaping from KVM, and Google Project Zero only talks about "When running with root privileges inside a KVM guest created using virt-manager on the Intel Haswell Xeon CPU, with a specific (now outdated) version of Debian's distro kernel running on the host, can read host kernel memory". there will likely be a Qemu update that mitigates some of the Spectre attack vectors in combination with microcode updates, but again - there are no public details yet regarding this (yet).
 
May 27, 2015
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there are no final public patches for Meltdown for either kernel 4.4 or 4.13 yet. once there are, we will review and include them ASAP.

Meltdown, which looks to be far more easily exploitable than Spectre, should not be usable from within KVM-enabled VMs to read host kernel memory, but containers are affected. compare the Xen advisory stating that only PV guests are affected by Meltdown (which they call "SP3").

concrete details regarding Spectre are still a bit rare, but AFAICT there are no public general PoCs yet allowing escaping from KVM, and Google Project Zero only talks about "When running with root privileges inside a KVM guest created using virt-manager on the Intel Haswell Xeon CPU, with a specific (now outdated) version of Debian's distro kernel running on the host, can read host kernel memory". there will likely be a Qemu update that mitigates some of the Spectre attack vectors in combination with microcode updates, but again - there are no public details yet regarding this (yet).

According to this, I assume we should make sure to have all VM CPUs set to kvm64 instead of host, isn't it?

Thank you
 

Symbol

Active Member
Mar 1, 2017
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According to this, I assume we should make sure to have all VM CPUs set to kvm64 instead of host, isn't it?
I don't think so, as you probably want to have pcid CPU flag exposed to your guests in order to mitigate the performance loss coming from the Kernel/User page tables isolation feature once your guest kernels are updated.
 
May 27, 2015
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I don't think so, as you probably want to have pcid CPU flag exposed to your guests in order to mitigate the performance loss coming from the Kernel/User page tables isolation feature once your guest kernels are updated.

But until the patch is released and hosts are upgraded, can anyone confirm if setting cpu to "kvm64" instead of "host" a temporary way to secure KVM VMs?

Thank you!
 

aderumier

Active Member
May 14, 2013
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cpumodel=kvm64 protected you against spectre in your vm, but not meltdown. (you need to patch your guest kernel)

host kernel need to be updated to avoid that a vm access to memory of another vm.
 
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