CVE-2026-99178 x86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context
MediumCVSS 6.5
EPSS 0.17%
- Published
- Updated
- Exploit status
- No public exploit known
Description
In the Linux kernel, the following vulnerability has been resolved:
x86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context
An async #PF "page not present" event arrives through the #PF vector,
and its reason sits in the per-CPU apf_reason.flags until
__kvm_handle_async_pf() reads and clears it. If an NMI arrives after
the event is injected and before the #PF handler reads the flags, and
the NMI handler itself takes a #PF, that fault reads and clears the
flags belonging to the #PF it interrupted. It then finds interrupts
disabled in the NMI context it interrupted, and panics:
Kernel panic - not syncing: Host injected async #PF in interrupt
disabled region
Call Trace:
<NMI>
panic+0x52/0x60
__kvm_handle_async_pf+0xb0/0xb0
exc_page_fault+0x71/0xb0
asm_exc_page_fault+0x27/0x30
RIP: 0010:__get_user_nocheck_8+0x6/0x20
perf_callchain_user+0x147/0x1a0
get_perf_callchain+0x12d/0x1c0
...
perf_event_nmi_handler+0x26/0x50
exc_nmi+0xe8/0x110
RIP: 0010:asm_exc_page_fault+0x0/0x30
</NMI>
The last RIP line shows the NMI landing on the first instruction of
the #PF entry. perf with user call chains takes such a fault: the
sampling NMI walks the user stack with __get_user(), which faults when
a saved frame pointer is not a valid user address or the walk runs off
the top of the stack. The same window exists when KVM, running as an
L1 hypervisor with DELIVERY_AS_PF_VMEXIT, reads the flags itself after
a #PF VM-exit.
The NMI entry code saves and restores CR2 for this nesting, but not the
async #PF reason. Andy Lutomirski described the race, with perf as the
example, when async #PF delivery was reworked in 2020 [1]. Saving and
clearing the flags across the NMI, next to CR2, was discussed there but
not merged.
Since that rework, Linux has stopped setting KVM_ASYNC_PF_SEND_ALWAYS,
so the host delivers "page not present" only for user mode faults and
a kernel-mode fault in NMI context (including kernel-mode #MC and #DB)
cannot be an async page fault. In that case, return without touching
the flags so that the interrupted handler finds them intact.
Tested on v7.3-rc5 in a 4-vCPU, 2 GiB guest restored from a snapshot
whose memory is served on demand through userfaultfd, so that reading
it back takes async #PFs, while every thread samples hardware cycles
with user call chains and points its frame pointer at an unmapped page.
Without this patch the guest panicked as above in 3 of 3 runs. With it,
the guest survived 3 of 3 runs of 60 seconds, and the host counted
148,441 to 153,334 kvm_async_pf_not_present events in the first 20
seconds of each. On 6.18.50 the results were the same: the guest
panicked without the patch and survived with it.
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| Linux kernel | >= 631bc4878220932fe67fc46fc7cf7cccdb1ec597, < fd60b32a99627fda479c9fa1d4a82fa9f7994670 | fd60b32a99627fda479c9fa1d4a82fa9f7994670 |
| Linux kernel | >= 631bc4878220932fe67fc46fc7cf7cccdb1ec597, < b77e9622bbade9812e2090c66d25c372f515e921 | b77e9622bbade9812e2090c66d25c372f515e921 |
| Linux kernel | >= 631bc4878220932fe67fc46fc7cf7cccdb1ec597, < f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9 | f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9 |
| Linux kernel | >= 631bc4878220932fe67fc46fc7cf7cccdb1ec597, < 81d99abe2bd81379abfb595e403bbbee6fbfc624 | 81d99abe2bd81379abfb595e403bbbee6fbfc624 |
| Linux kernel | = 2.6.38 | No fix listed |
| Linux kernel | < 6.12.115 | 6.12.115 |
| Linux kernel | < 6.18.59 | 6.18.59 |
| Linux kernel | < 7.2.13 | 7.2.13 |
| Linux kernel | < 7.3 | 7.3 |
| ubuntu/linux(Ubuntu:22.04) | All versions | No fix listed |
| ubuntu/linux-kvm(Ubuntu:22.04) | All versions | No fix listed |
| ubuntu/linux-raspi(Ubuntu:22.04) | All versions | No fix listed |
| ubuntu/linux(Ubuntu:24.04) | All versions | No fix listed |
| ubuntu/linux-raspi(Ubuntu:24.04) | All versions | No fix listed |
| debian/linux(Debian:12) | All versions | No fix listed |
| debian/linux(Debian:12) | = 6.1.106-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.106-2 | No fix listed |
| debian/linux(Debian:12) | = 6.1.106-3 | No fix listed |
| debian/linux(Debian:12) | = 6.1.112-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.115-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.119-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.123-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.124-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.128-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.129-1 | No fix listed |
Show 175 more
| Product | Affected versions | Fixed in |
|---|---|---|
| debian/linux(Debian:12) | = 6.1.133-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.135-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.137-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.139-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.140-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.147-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.148-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.153-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.158-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.159-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.162-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.164-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.170-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.170-2 | No fix listed |
| debian/linux(Debian:12) | = 6.1.170-3 | No fix listed |
| debian/linux(Debian:12) | = 6.1.172-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.174-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.176-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.177-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.180-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.187-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.190-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.27-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.37-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.38-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.38-2 | No fix listed |
| debian/linux(Debian:12) | = 6.1.38-2~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.38-3 | No fix listed |
| debian/linux(Debian:12) | = 6.1.38-4 | No fix listed |
| debian/linux(Debian:12) | = 6.1.38-4~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.52-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.55-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.55-1~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.64-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.66-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.67-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.69-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.69-1~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.76-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.76-1~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.82-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.85-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.90-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.90-1~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.94-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.94-1~bpo11+1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.98-1 | No fix listed |
| debian/linux(Debian:12) | = 6.1.99-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.1-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.11-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.11-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.12-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.3-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.4-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.6-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.6-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.7-1 | No fix listed |
| debian/linux(Debian:12) | = 6.10.9-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.10-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.10-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.2-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.4-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.5-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.5-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.6-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.7-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11.9-1 | No fix listed |
| debian/linux(Debian:12) | = 6.11~rc4-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.11~rc5-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.10-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.100-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.101-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.105-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.107-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.11-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.11-1+alpha | No fix listed |
| debian/linux(Debian:12) | = 6.12.11-1+alpha.1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.111-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.113-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.115-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.115-2 | No fix listed |
| debian/linux(Debian:12) | = 6.12.116-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.12-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.12-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.13-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.15-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.16-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.17-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.19-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.20-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.21-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.22-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.22-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.25-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.27-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.27-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.29-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.3-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.30-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.30-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.31-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.32-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.32-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.33-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.33-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.35-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.35-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.37-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.38-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.38-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.41-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.43-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.43-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.48-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.5-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.57-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.57-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.6-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.63-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.63-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.69-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.69-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.73-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.73-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.74-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.74-2 | No fix listed |
| debian/linux(Debian:12) | = 6.12.74-2~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.8-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.85-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.85-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.86-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.86-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.88-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.88-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.9-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.9-1+alpha | No fix listed |
| debian/linux(Debian:12) | = 6.12.9-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.90-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.90-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.90-2 | No fix listed |
| debian/linux(Debian:12) | = 6.12.90-2~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.94-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.94-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.95-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.95-1~bpo12+1 | No fix listed |
| debian/linux(Debian:12) | = 6.12.96-1 | No fix listed |
| debian/linux(Debian:12) | = 6.12~rc6-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.10-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.11-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.2-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.3-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.4-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.5-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.6-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.7-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.8-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13.9-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13~rc6-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.13~rc7-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.14.3-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.14.5-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.14.6-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15.1-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15.2-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15.3-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15.4-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15.5-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15.6-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.15~rc7-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.16-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.16.1-1~exp1 | No fix listed |
| debian/linux(Debian:12) | = 6.16.10-1 | No fix listed |
References
- MSRC Security Update Guide vendor-advisory
- Release Notes vendor-advisory
- Red Hat CVE page vendor-advisory
- Red Hat Bugzilla 2562721 issue-tracking
- www.cve.org
- nvd.nist.gov
- git.kernel.org
- git.kernel.org
- git.kernel.org
- git.kernel.org
- git.kernel.org
- Debian Security Tracker CVE-2026-99178 vendor-advisory
- Ubuntu CVE tracker vendor-advisory