CVE-2025-38455 Information

Jul 26, 2025 cve

Description

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: 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 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—

Reference

https://git.kernel.org/stable/c/8c8e8d4d7544bb783e15078eda8ba2580e192246 https://git.kernel.org/stable/c/b5725213149597cd9c2b075b87bc4e0f87e906c1 https://git.kernel.org/stable/c/e0d9a7cf37ca09c513420dc88e0d0e805a4f0820 https://git.kernel.org/stable/c/ecf371f8b02d5e31b9aa1da7f159f1b2107bdb01 https://git.kernel.org/stable/c/fd044c99d831e9f837518816c7c366b04014d405

CNNVD-202507-3306 (Published: 2025-07-25)

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