CVE-2026-43315

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...