CVE-2025-38455 in Linux
Summary
by MITRE • 07/25/2025
In the Linux kernel, the following vulnerability has been resolved:
KVM: SVM: Reject SEV{-ES} intra host migration if vCPU creation is in-flight
Reject migration of SEV{-ES} state if either the source or destination VM
is actively creating a vCPU, i.e. if kvm_vm_ioctl_create_vcpu() is in the section between incrementing created_vcpus and online_vcpus. The bulk of vCPU creation runs _outside_ of kvm->lock to allow creating multiple vCPUs in parallel, and so sev_info.es_active can get toggled from false=>true in the destination VM after (or during) svm_vcpu_create(), resulting in an SEV{-ES} VM effectively having a non-SEV{-ES} vCPU.
The issue manifests most visibly as a crash when trying to free a vCPU's NULL VMSA page in an SEV-ES VM, but any number of things can go wrong.
BUG: unable to handle page fault for address: ffffebde00000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP KASAN NOPTI
CPU: 227 UID: 0 PID: 64063 Comm: syz.5.60023 Tainted: G U O 6.15.0-smp-DEV #2 NONE Tainted: [U]=USER, [O]=OOT_MODULE
Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 12.52.0-0 10/28/2024 RIP: 0010:constant_test_bit arch/x86/include/asm/bitops.h:206 [inline]
RIP: 0010:arch_test_bit arch/x86/include/asm/bitops.h:238 [inline]
RIP: 0010:_test_bit include/asm-generic/bitops/instrumented-non-atomic.h:142 [inline]
RIP: 0010:PageHead include/linux/page-flags.h:866 [inline]
RIP: 0010:___free_pages+0x3e/0x120 mm/page_alloc.c:5067 Code: <49> f7 06 40 00 00 00 75 05 45 31 ff eb 0c 66 90 4c 89 f0 4c 39 f0 RSP: 0018:ffff8984551978d0 EFLAGS: 00010246 RAX: 0000777f80000001 RBX: 0000000000000000 RCX: ffffffff918aeb98 RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffebde00000000 RBP: 0000000000000000 R08: ffffebde00000007 R09: 1ffffd7bc0000000 R10: dffffc0000000000 R11: fffff97bc0000001 R12: dffffc0000000000 R13: ffff8983e19751a8 R14: ffffebde00000000 R15: 1ffffd7bc0000000 FS: 0000000000000000(0000) GS:ffff89ee661d3000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffebde00000000 CR3: 000000793ceaa000 CR4: 0000000000350ef0 DR0: 0000000000000000 DR1: 0000000000000b5f DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Call Trace: <TASK> sev_free_vcpu+0x413/0x630 arch/x86/kvm/svm/sev.c:3169 svm_vcpu_free+0x13a/0x2a0 arch/x86/kvm/svm/svm.c:1515 kvm_arch_vcpu_destroy+0x6a/0x1d0 arch/x86/kvm/x86.c:12396 kvm_vcpu_destroy virt/kvm/kvm_main.c:470 [inline]
kvm_destroy_vcpus+0xd1/0x300 virt/kvm/kvm_main.c:490 kvm_arch_destroy_vm+0x636/0x820 arch/x86/kvm/x86.c:12895 kvm_put_kvm+0xb8e/0xfb0 virt/kvm/kvm_main.c:1310 kvm_vm_release+0x48/0x60 virt/kvm/kvm_main.c:1369 __fput+0x3e4/0x9e0 fs/file_table.c:465 task_work_run+0x1a9/0x220 kernel/task_work.c:227 exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x7f0/0x25b0 kernel/exit.c:953 do_group_exit+0x203/0x2d0 kernel/exit.c:1102 get_signal+0x1357/0x1480 kernel/signal.c:3034 arch_do_signal_or_restart+0x40/0x690 arch/x86/kernel/signal.c:337 exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x67/0xb0 kernel/entry/common.c:218 do_syscall_64+0x7c/0x150 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0033:0x7f87a898e969 </TASK> Modules linked in: gq(O) gsmi: Log Shutdown Reason 0x03 CR2: ffffebde00000000 ---[ end trace 0000000000000000 ]---
Deliberately don't check for a NULL VMSA when freeing the vCPU, as crashing the host is likely desirable due to the VMSA being consumed by hardware. E.g. if KVM manages to allow VMRUN on the vCPU, hardware may read/write a bogus VMSA page. Accessing P ---truncated---
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Analysis
by VulDB Data Team • 01/03/2026
The vulnerability CVE-2025-38455 affects the Linux kernel's KVM hypervisor implementation, specifically within the SVM (Secure Virtual Machine) module used for AMD virtualization. This flaw arises during SEV (Secure Encrypted Virtualization) and SEV-ES (SEV Encrypted State) migration operations, where the system fails to properly validate vCPU creation states. The core issue occurs when a virtual machine attempts to migrate its SEV{-ES} state while a vCPU creation process is actively in progress, creating a race condition that can lead to inconsistent virtual machine states.
The technical root cause involves the timing of vCPU creation operations within the KVM subsystem. The kernel's vCPU creation process executes portions outside of the main kvm->lock to enable parallel processing of multiple vCPUs, but this design creates a window where sev_info.es_active can be toggled from false to true in the destination VM after the svm_vcpu_create() function completes. This inconsistency causes SEV{-ES} virtual machines to effectively contain non-SEV{-ES} vCPUs, leading to critical state mismatches. The vulnerability manifests as a kernel oops or system crash when attempting to free a vCPU's NULL VMSA (Virtual Machine Save Area) page, which is a critical memory structure used in SEV-ES implementations.
The operational impact of this vulnerability is severe, as it can result in system crashes, potential data corruption, and hardware-level security breaches. When a vCPU's VMSA page is accessed after improper state transitions, the kernel generates page fault exceptions that typically result in system panics. The described crash pattern shows memory access violations at specific addresses, indicating that the hypervisor is attempting to operate on invalid memory regions. According to CWE classification, this represents a race condition vulnerability (CWE-362) that can lead to memory corruption and privilege escalation, while ATT&CK framework categorizes this under privilege escalation through hypervisor flaws (T1059.001).
Mitigation strategies must focus on preventing migration operations during active vCPU creation phases. The kernel patch implements a validation check that rejects SEV{-ES} intra-host migrations when either the source or destination VM is in the process of creating vCPUs, specifically during the window between created_vcpus and online_vcpus increments. This prevents the race condition that leads to inconsistent SEV{-ES} states. System administrators should ensure all virtual machines running SEV{-ES} workloads are updated to kernel versions containing this fix, and consider implementing additional monitoring for migration operations during high-vCPU creation periods. Organizations using KVM-based virtualization platforms must also verify that their hypervisor configurations properly enforce these state validation checks, as the vulnerability can be exploited to compromise the integrity of encrypted virtual machine workloads and potentially expose sensitive data processed within these environments.