CVE-2026-43315 - Vulnerability Details

- KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding

Description

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

KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding

Drop the WARN in svm_set_nested_state() on nested_svm_load_cr3() failing
as it is trivially easy to trigger from userspace by modifying CPUID after
loading CR3. E.g. modifying the state restoration selftest like so:

--- tools/testing/selftests/kvm/x86/state_test.c
+++ tools/testing/selftests/kvm/x86/state_test.c
@@ -280,7 +280,16 @@ int main(int argc, char *argv[])

/* Restore state in a new VM. */
vcpu = vm_recreate_with_one_vcpu(vm);
- vcpu_load_state(vcpu, state);
+
+ if (stage == 4) {
+ state->sregs.cr3 = BIT(44);
+ vcpu_load_state(vcpu, state);
+
+ vcpu_set_cpuid_property(vcpu, X86_PROPERTY_MAX_PHY_ADDR, 36);
+ __vcpu_nested_state_set(vcpu, &state->nested);
+ } else {
+ vcpu_load_state(vcpu, state);
+ }

/*
* Restore XSAVE state in a dummy vCPU, first without doing

generates:

WARNING: CPU: 30 PID: 938 at arch/x86/kvm/svm/nested.c:1877 svm_set_nested_state+0x34a/0x360 [kvm_amd]
Modules linked in: kvm_amd kvm irqbypass [last unloaded: kvm]
CPU: 30 UID: 1000 PID: 938 Comm: state_test Tainted: G W 6.18.0-rc7-58e10b63777d-next-vm
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:svm_set_nested_state+0x34a/0x360 [kvm_amd]
Call Trace:
<TASK>
kvm_arch_vcpu_ioctl+0xf33/0x1700 [kvm]
kvm_vcpu_ioctl+0x4e6/0x8f0 [kvm]
__x64_sys_ioctl+0x8f/0xd0
do_syscall_64+0x61/0xad0
entry_SYSCALL_64_after_hwframe+0x4b/0x53

Simply delete the WARN instead of trying to prevent userspace from shoving
"illegal" state into CR3. For better or worse, KVM's ABI allows userspace
to set CPUID after SREGS, and vice versa, and KVM is very permissive when
it comes to guest CPUID. I.e. attempting to enforce the virtual CPU model
when setting CPUID could break userspace. Given that the WARN doesn't
provide any meaningful protection for KVM or benefit for userspace, simply
drop it even though the odds of breaking userspace are minuscule.

Opportunistically delete a spurious newline.

Published: 2026-05-08

Score: n/a

EPSS: n/a

KEV: No

Impact:

Action:

Analysis

Impact

In the Linux kernel, a modification of CPUID after loading CR3 can trigger a WARN in the KVM AMD nested virtualization code. The warning does not block execution, does not alter privilege levels, and provides no meaningful protection for the kernel or its users. Consequently, it is considered a harmless diagnostic message rather than an exploit.

Affected Systems

The vulnerability affects any Linux kernel that includes the kvm_amd module before the fix that removes the warning, regardless of distribution. It is specifically relevant when KVM is used to run nested virtual machines, since the bug is triggered by manipulating CPUID after setting SREGS in a virtual CPU.

Risk and Exploitability

No CVSS score is provided, and the EPSS score is unavailable. The issue is not listed in CISA’s KEV catalog, indicating no known live exploits. Because the warning can be triggered from userspace but does not compromise kernel integrity or confidentiality, the risk of exploitation is negligible.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< 155ec243ef726f4bc49536fa0bfb565dc011ab17
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< 580ea57840864d40e019bc13fd26afdc8d510a2f
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< deb8f6dfd31d94b18dbeeaa8c01fbec5fc70fd2b
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< ce904c8a5bbe697eae0f7e34b07095bd7a6dee19
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< 969e5e13ff5c18603f21d1f9f64ec9194e141ac0
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< ebb2ab4f1c87d6b52776292cf7dc16aea48e95f8
`b222b0b88162bdef4eceb12a79d5edbbdb23dbfd`	affected	< fc3ba56385d03501eb582e4b86691ba378e556f9

Linux

affected

Version	Status	Constraints
`5.14`	affected	—
`0`	unaffected	< 5.14
`5.15.202`	unaffected	≤ 5.15.*
`6.1.165`	unaffected	≤ 6.1.*
`6.6.128`	unaffected	≤ 6.6.*
`6.12.75`	unaffected	≤ 6.12.*
`6.18.16`	unaffected	≤ 6.18.*
`6.19.6`	unaffected	≤ 6.19.*
`7.0`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,155ec243ef726f4bc49536fa0bfb565dc011ab17)`	affected	code_commit	—
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,580ea57840864d40e019bc13fd26afdc8d510a2f)`	affected	code_commit	—
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,deb8f6dfd31d94b18dbeeaa8c01fbec5fc70fd2b)`	affected	code_commit	—
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,ce904c8a5bbe697eae0f7e34b07095bd7a6dee19)`	affected	code_commit	—
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,969e5e13ff5c18603f21d1f9f64ec9194e141ac0)`	affected	code_commit	—
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,ebb2ab4f1c87d6b52776292cf7dc16aea48e95f8)`	affected	code_commit	—
`[b222b0b88162bdef4eceb12a79d5edbbdb23dbfd,fc3ba56385d03501eb582e4b86691ba378e556f9)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`5.14`	affected	generic	—
`[0,5.14)`	unaffected	generic	—
`[5.15.202,6.0.0)`	unaffected	semver	—
`[6.1.165,6.2.0)`	unaffected	semver	—
`[6.6.128,6.7.0)`	unaffected	semver	—
`[6.12.75,6.13.0)`	unaffected	semver	—
`[6.18.16,6.19.0)`	unaffected	semver	—
`[6.19.6,6.20.0)`	unaffected	semver	—
`[7.0,*)`	unaffected	generic	—

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Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

Upgrade the Linux kernel to a version that includes the patch removing the WARN in KVM AMD nested virtualization.
Restart any KVM‑based virtual machine services to ensure the updated kernel module is loaded.
Monitor system logs for the “WARNING: CPU” message; if it persists, verify that the latest kernel is in use and consider suppressing such warnings via syslog configuration.

Generated by OpenCVE AI on May 8, 2026 at 15:07 UTC.

Tracking

Sign in to view the affected projects.

Advisories

No advisories yet.

No CVSS v4.0

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/155ec243ef726f4bc49536fa0bfb565dc011ab17
https://git.kernel.org/stable/c/580ea57840864d40e019bc13fd26afdc8d510a2f
https://git.kernel.org/stable/c/969e5e13ff5c18603f21d1f9f64ec9194e141ac0
https://git.kernel.org/stable/c/ce904c8a5bbe697eae0f7e34b07095bd7a6dee19
https://git.kernel.org/stable/c/deb8f6dfd31d94b18dbeeaa8c01fbec5fc70fd2b
https://git.kernel.org/stable/c/ebb2ab4f1c87d6b52776292cf7dc16aea48e95f8
https://git.kernel.org/stable/c/fc3ba56385d03501eb582e4b86691ba378e556f9

History

Fri, 08 May 2026 15:30:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-488

Fri, 08 May 2026 13:30:00 +0000

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding Drop the WARN in svm_set_nested_state() on nested_svm_load_cr3() failing as it is trivially easy to trigger from userspace by modifying CPUID after loading CR3. E.g. modifying the state restoration selftest like so: --- tools/testing/selftests/kvm/x86/state_test.c +++ tools/testing/selftests/kvm/x86/state_test.c @@ -280,7 +280,16 @@ int main(int argc, char argv[]) / Restore state in a new VM. / vcpu = vm_recreate_with_one_vcpu(vm); - vcpu_load_state(vcpu, state); + + if (stage == 4) { + state->sregs.cr3 = BIT(44); + vcpu_load_state(vcpu, state); + + vcpu_set_cpuid_property(vcpu, X86_PROPERTY_MAX_PHY_ADDR, 36); + __vcpu_nested_state_set(vcpu, &state->nested); + } else { + vcpu_load_state(vcpu, state); + } / * Restore XSAVE state in a dummy vCPU, first without doing generates: WARNING: CPU: 30 PID: 938 at arch/x86/kvm/svm/nested.c:1877 svm_set_nested_state+0x34a/0x360 [kvm_amd] Modules linked in: kvm_amd kvm irqbypass [last unloaded: kvm] CPU: 30 UID: 1000 PID: 938 Comm: state_test Tainted: G W 6.18.0-rc7-58e10b63777d-next-vm Tainted: [W]=WARN Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:svm_set_nested_state+0x34a/0x360 [kvm_amd] Call Trace: <TASK> kvm_arch_vcpu_ioctl+0xf33/0x1700 [kvm] kvm_vcpu_ioctl+0x4e6/0x8f0 [kvm] __x64_sys_ioctl+0x8f/0xd0 do_syscall_64+0x61/0xad0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Simply delete the WARN instead of trying to prevent userspace from shoving "illegal" state into CR3. For better or worse, KVM's ABI allows userspace to set CPUID after SREGS, and vice versa, and KVM is very permissive when it comes to guest CPUID. I.e. attempting to enforce the virtual CPU model when setting CPUID could break userspace. Given that the WARN doesn't provide any meaningful protection for KVM or benefit for userspace, simply drop it even though the odds of breaking userspace are minuscule. Opportunistically delete a spurious newline.
Title		KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/155ec243ef726f4bc49536fa0bfb565dc011ab17 https://git.kernel.org/stable/c/580ea57840864d40e019bc13fd26afdc8d510a2f https://git.kernel.org/stable/c/969e5e13ff5c18603f21d1f9f64ec9194e141ac0 https://git.kernel.org/stable/c/ce904c8a5bbe697eae0f7e34b07095bd7a6dee19 https://git.kernel.org/stable/c/deb8f6dfd31d94b18dbeeaa8c01fbec5fc70fd2b https://git.kernel.org/stable/c/ebb2ab4f1c87d6b52776292cf7dc16aea48e95f8 https://git.kernel.org/stable/c/fc3ba56385d03501eb582e4b86691ba378e556f9

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-05-08T13:11:31.784Z

Updated: 2026-05-08T13:11:31.784Z

Reserved: 2026-05-01T14:12:56.001Z

Link: CVE-2026-43315

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-05-08T14:16:39.977

Modified: 2026-05-08T14:16:39.977

Link: CVE-2026-43315

Redhat

No data.

OpenCVE Enrichment

Updated: 2026-05-08T16:00:12Z

Weaknesses

CWE-488

Impact

Affected Systems

Risk and Exploitability

Tracking

Subscriptions

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