Skip to content
Fencer Intel
medium 5.5

CVE-2024-26991 json

KVM: x86/mmu: x86: Don't overflow lpage_info when checking attributes

published 2y ago modified 4mo ago also EUVD-2024-24253

cvss
5.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: x86: Don't overflow lpage_info when checking attributes

Fix KVM_SET_MEMORY_ATTRIBUTES to not overflow lpage_info array and trigger KASAN splat, as seen in the private_mem_conversions_test selftest.

When memory attributes are set on a GFN range, that range will have specific properties applied to the TDP. A huge page cannot be used when the attributes are inconsistent, so they are disabled for those the specific huge pages. For internal KVM reasons, huge pages are also not allowed to span adjacent memslots regardless of whether the backing memory could be mapped as huge.

What GFNs support which huge page sizes is tracked by an array of arrays 'lpage_info' on the memslot, of ‘kvm_lpage_info’ structs. Each index of lpage_info contains a vmalloc allocated array of these for a specific supported page size. The kvm_lpage_info denotes whether a specific huge page (GFN and page size) on the memslot is supported. These arrays include indices for unaligned head and tail huge pages.

Preventing huge pages from spanning adjacent memslot is covered by incrementing the count in head and tail kvm_lpage_info when the memslot is allocated, but disallowing huge pages for memory that has mixed attributes has to be done in a more complicated way. During the KVM_SET_MEMORY_ATTRIBUTES ioctl KVM updates lpage_info for each memslot in the range that has mismatched attributes. KVM does this a memslot at a time, and marks a special bit, KVM_LPAGE_MIXED_FLAG, in the kvm_lpage_info for any huge page. This bit is essentially a permanently elevated count. So huge pages will not be mapped for the GFN at that page size if the count is elevated in either case: a huge head or tail page unaligned to the memslot or if KVM_LPAGE_MIXED_FLAG is set because it has mixed attributes.

To determine whether a huge page has consistent attributes, the KVM_SET_MEMORY_ATTRIBUTES operation checks an xarray to make sure it consistently has the incoming attribute. Since level - 1 huge pages are aligned to level huge pages, it employs an optimization. As long as the level - 1 huge pages are checked first, it can just check these and assume that if each level - 1 huge page contained within the level sized huge page is not mixed, then the level size huge page is not mixed. This optimization happens in the helper hugepage_has_attrs().

Unfortunately, although the kvm_lpage_info array representing page size 'level' will contain an entry for an unaligned tail page of size level, the array for level - 1 will not contain an entry for each GFN at page size level. The level - 1 array will only contain an index for any unaligned region covered by level - 1 huge page size, which can be a smaller region. So this causes the optimization to overflow the level - 1 kvm_lpage_info and perform a vmalloc out of bounds read.

In some cases of head and tail pages where an overflow could happen, callers skip the operation completely as KVM_LPAGE_MIXED_FLAG is not required to prevent huge pages as discussed earlier. But for memslots that are smaller than the 1GB page size, it does call hugepage_has_attrs(). In this case the huge page is both the head and tail page. The issue can be observed simply by compiling the kernel with CONFIG_KASAN_VMALLOC and running the selftest “private_mem_conversions_test”, which produces the output like the following:

BUG: KASAN: vmalloc-out-of-bounds in hugepage_has_attrs+0x7e/0x110 Read of size 4 at addr ffffc900000a3008 by task private_mem_con/169 Call Trace: dump_stack_lvl print_report ? __virt_addr_valid ? hugepage_has_attrs ? hugepage_has_attrs kasan_report ? hugepage_has_attrs hugepage_has_attrs kvm_arch_post_set_memory_attributes kvm_vm_ioctl

It is a little ambiguous whether the unaligned head page (in the bug case also the tail page) should be expected to have KVM_LPAGE_MIXED_FLAG set. It is not functionally required, as the unal ---truncated---

Patch / fix

  • Linux Linux 6.8.8, 6.9
  • linux Debian 14, Debian 13 6.8.9-1

debian advisories DEBIAN-CVE-2024-26991

  • linux Ubuntu 24.04 LTS 6.8.0-38.38
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1011.12
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1010.11
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1006.9
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1008.8
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1010.10
  • linux-intel Ubuntu 24.04 LTS 6.8.0-1007.14
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1007.7

ubuntu advisories UBUNTU-CVE-2024-26991

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 9 5.14.0-427.37.1.el9_4
  • rv RHEL 9 5.14.0-427.37.1.el9_4
  • perf RHEL 9 5.14.0-427.37.1.el9_4
  • rtla RHEL 9 5.14.0-427.37.1.el9_4
  • bpftool RHEL 9 7.3.0-427.37.1.el9_4
  • libperf RHEL 9 5.14.0-427.37.1.el9_4
  • kernel-rt RHEL 9 5.14.0-427.37.1.el9_4
  • kernel-64k RHEL 9 5.14.0-427.37.1.el9_4

red hat advisories RHSA-2024:6997

  • kernel-rt Linux Micro 6.0 6.4.0-9.1
  • kernel-source-rt Linux Micro 6.0 6.4.0-9.1
  • kernel-source Linux Micro 6.0 6.4.0-18.1
  • kernel-default Linux Micro 6.0 6.4.0-18.1
  • kernel-kvmsmall Linux Micro 6.0 6.4.0-18.1
  • kernel-default-base Linux Micro 6.0 6.4.0-17.1.1.51
  • kernel-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.5.1
  • kernel-syms-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.5.1

suse advisories SUSE-SU-2025:20028-1SUSE-SU-2025:20008-1SUSE-SU-2024:2973-1SUSE-SU-2024:2203-1SUSE-SU-2024:2135-1

  • kernel AlmaLinux 9 5.14.0-427.37.1.el9_4
  • rv AlmaLinux 9 5.14.0-427.37.1.el9_4
  • perf AlmaLinux 9 5.14.0-427.37.1.el9_4
  • rtla AlmaLinux 9 5.14.0-427.37.1.el9_4
  • bpftool AlmaLinux 9 7.3.0-427.37.1.el9_4
  • libperf AlmaLinux 9 5.14.0-427.37.1.el9_4
  • kernel-rt AlmaLinux 9 5.14.0-427.37.1.el9_4
  • kernel-64k AlmaLinux 9 5.14.0-427.37.1.el9_4

almalinux advisories ALSA-2024:6997

Is CVE-2024-26991 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2024-26991 updated cvss 5.5

kernel: KVM: x86/mmu: x86: Don't overflow lpage_info when checking attributes

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-427.37.1.el9_4, perf 5.14.0-427.37.1.el9_4, rtla 5.14.0-427.37.1.el9_4, kernel-devel-matched 5.14.0-427.37.1.el9_4, kernel-64k-devel-matched 5.14.0-427.37.1.el9_4, kernel-debug-devel-matched 5.14.0-427.37.1.el9_4, +6 more Red Hat Enterprise Linux BaseOS (v. 9) bpftool 7.3.0-427.37.1.el9_4, kernel 5.14.0-427.37.1.el9_4, kernel-64k 5.14.0-427.37.1.el9_4, kernel-core 5.14.0-427.37.1.el9_4, kernel-tools 5.14.0-427.37.1.el9_4, python3-perf 5.14.0-427.37.1.el9_4, +28 more Red Hat Enterprise Linux CRB (v. 9) libperf 5.14.0-427.37.1.el9_4, kernel-debuginfo-common-s390x 5.14.0-427.37.1.el9_4, kernel-debuginfo-common-x86_64 5.14.0-427.37.1.el9_4, kernel-debuginfo-common-aarch64 5.14.0-427.37.1.el9_4, kernel-debuginfo-common-ppc64le 5.14.0-427.37.1.el9_4 Red Hat Enterprise Linux NFV (v. 9) kernel-rt 5.14.0-427.37.1.el9_4, kernel-rt-kvm 5.14.0-427.37.1.el9_4, kernel-rt-core 5.14.0-427.37.1.el9_4, kernel-rt-modules 5.14.0-427.37.1.el9_4, kernel-rt-debug-kvm 5.14.0-427.37.1.el9_4, kernel-rt-debug-core 5.14.0-427.37.1.el9_4, +6 more Red Hat Enterprise Linux RT (v. 9) kernel-rt 5.14.0-427.37.1.el9_4, kernel-rt-core 5.14.0-427.37.1.el9_4, kernel-rt-modules 5.14.0-427.37.1.el9_4, kernel-rt-debug-core 5.14.0-427.37.1.el9_4, kernel-rt-modules-core 5.14.0-427.37.1.el9_4, kernel-rt-debug-modules 5.14.0-427.37.1.el9_4, +4 more
    fixed: vendor fix RHSA-2024:6997
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2y ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.