CVE-2025-38455

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---