CVE-2026-43315

Full vulnerability record from the local CVENow database.

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.

Severity

MEDIUM

CVSS score

5.5 (v3.1)

Vulnerability status

Analyzed

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2026-05-08 14:16:39.977000

Last modified

2026-11-06 16:18:34.357000

View original CVE JSON

{
  "id": "CVE-2026-43315",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-05-08T14:16:39.977",
  "lastModified": "2026-11-06T16:18:34.357",
  "vulnStatus": "Analyzed",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding\n\nDrop the WARN in svm_set_nested_state() on nested_svm_load_cr3() failing\nas it is trivially easy to trigger from userspace by modifying CPUID after\nloading CR3.  E.g. modifying the state restoration selftest like so:\n\n  --- tools/testing/selftests/kvm/x86/state_test.c\n  +++ tools/testing/selftests/kvm/x86/state_test.c\n  @@ -280,7 +280,16 @@ int main(int argc, char *argv[])\n\n                 /* Restore state in a new VM.  */\n                  vcpu = vm_recreate_with_one_vcpu(vm);\n  -               vcpu_load_state(vcpu, state);\n  +\n  +               if (stage == 4) {\n  +                       state->sregs.cr3 = BIT(44);\n  +                       vcpu_load_state(vcpu, state);\n  +\n  +                       vcpu_set_cpuid_property(vcpu, X86_PROPERTY_MAX_PHY_ADDR, 36);\n  +                       __vcpu_nested_state_set(vcpu, &state->nested);\n  +               } else {\n  +                       vcpu_load_state(vcpu, state);\n  +               }\n\n                  /*\n                   * Restore XSAVE state in a dummy vCPU, first without doing\n\ngenerates:\n\n  WARNING: CPU: 30 PID: 938 at arch/x86/kvm/svm/nested.c:1877 svm_set_nested_state+0x34a/0x360 [kvm_amd]\n  Modules linked in: kvm_amd kvm irqbypass [last unloaded: kvm]\n  CPU: 30 UID: 1000 PID: 938 Comm: state_test Tainted: G        W           6.18.0-rc7-58e10b63777d-next-vm\n  Tainted: [W]=WARN\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n  RIP: 0010:svm_set_nested_state+0x34a/0x360 [kvm_amd]\n  Call Trace:\n   <TASK>\n   kvm_arch_vcpu_ioctl+0xf33/0x1700 [kvm]\n   kvm_vcpu_ioctl+0x4e6/0x8f0 [kvm]\n   __x64_sys_ioctl+0x8f/0xd0\n   do_syscall_64+0x61/0xad0\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nSimply delete the WARN instead of trying to prevent userspace from shoving\n\"illegal\" state into CR3.  For better or worse, KVM's ABI allows userspace\nto set CPUID after SREGS, and vice versa, and KVM is very permissive when\nit comes to guest CPUID.  I.e. attempting to enforce the virtual CPU model\nwhen setting CPUID could break userspace.  Given that the WARN doesn't\nprovide any meaningful protection for KVM or benefit for userspace, simply\ndrop it even though the odds of breaking userspace are minuscule.\n\nOpportunistically delete a spurious newline."
    }
  ],
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          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
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          "role": "CISA Coordinator",
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      "source": "[email protected]",
      "type": "Primary",
      "description": [
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          "lang": "en",
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