Bugzilla – Bug 1183071
VUL-0: CVE-2021-28039: xen: Linux: special config may crash when trying to map foreign pages (XSA-369)
Last modified: 2022-01-11 14:10:00 UTC
Created attachment 846821 [details]
Xen Security Advisory XSA-369
Linux: special config may crash when trying to map foreign pages
With CONFIG_XEN_BALLOON_MEMORY_HOTPLUG disabled and
CONFIG_XEN_UNPOPULATED_ALLOC enabled the Linux kernel will use guest
physical addresses allocated via the ZONE_DEVICE functionality for
mapping foreign guest's pages.
This will result in problems, as the p2m list will only cover the initial
memory size of the domain plus some padding at the end. Most ZONE_DEVICE
allocated addresses will be outside the p2m range and thus a mapping can't
be established with those memory addresses, resulting in a crash.
The attack involves doing I/O requiring large amounts of data to be
mapped by the Dom0 or driver domain. The amount of data needed to
result in a crash can vary depending on the memory layout of the
affected Dom0 or driver domain.
A Dom0 or driver domain based on a Linux kernel (configured as
described above) can be crashed by a malicious guest administrator, or
possibly malicious unprivileged guest processes.
Only x86 paravirtualized (PV) Dom0 or driver domains are
Only Linux kernels configured *with* CONFIG_XEN_UNPOPULATED_ALLOC and
*without* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG are vulnerable. Only
kernels from kernel version 5.9 onwards are affected.
CONFIG_XEN_BALLOON_MEMORY_HOTPLUG is enabled by default in upstream
Linux when Xen support is enabled, so kernels using upstream default
Kconfig are not affected. Most distribution kernels supporting Xen
dom0 use are likewise not vulnerable.
Arm systems or x86 PVH or x86 HVM driver domains are not affected.
There is no mitigation available.
Applying the appropriate attached patch resolves this issue.
xsa369-linux.patch Linux 5.9-stable - 5.12-rc
$ sha256sum xsa369*
This issue was discovered by Marek Marczykowski-Górecki of Invisible
Reported-by: Marek Marczykowski-Górecki <firstname.lastname@example.org>
NOTE REGARDING LACK OF EMBARGO
This was reported publicly multiple times, before the XSA could be
@kernel-bugs: also looks like a duplicate, for bsc#1183035
As only kernels from 5.9 onwards are affected, I don't see any action on our side to be necessary.
(In reply to Jürgen Groß from comment #5)
> As only kernels from 5.9 onwards are affected, I don't see any action on our
> side to be necessary.
What about the master and stable branches? Or we don't support them with Xen?
master and stable will get the fix rather soon via upstream. The patches have already been taken there.
The issue itself is of rather low severity and our default kernel config is not affected by the issue.
Ok, good, I guess we're done here then. Bouncing back.
*** Bug 1183035 has been marked as a duplicate of this bug. ***
nothing to do, closing