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.
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.
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 | Linux | unaffected |
|
||||||||||||||||||||||||||||||
| Linux | Linux | affected |
|
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Advisories
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Fixes
Solution
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Workaround
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References
History
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 |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
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
No data.
Weaknesses
No weakness.