KVM: SVM: Get source vCPUs from source VM for SEV-ES intrahost migration

In the Linux kernel, the following vulnerability has been resolved:

KVM: SVM: Get source vCPUs from source VM for SEV-ES intrahost migration

Fix a goof where KVM tries to grab source vCPUs from the destination VM

when doing intrahost migration. Grabbing the wrong vCPU not only hoses

the guest, it also crashes the host due to the VMSA pointer being left

NULL.

BUG: unable to handle page fault for address: ffffe38687000000

#PF: supervisor read access in kernel mode

#PF: error_code(0x0000) - not-present page

PGD 0 P4D 0

Oops: 0000 [#1] SMP NOPTI

CPU: 39 PID: 17143 Comm: sev_migrate_tes Tainted: GO 6.5.0-smp--fff2e47e6c3b-next #151

Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.28.0 07/10/2023

RIP: 0010:__free_pages+0x15/0xd0

RSP: 0018:ffff923fcf6e3c78 EFLAGS: 00010246

RAX: 0000000000000000 RBX: ffffe38687000000 RCX: 0000000000000100

RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffffe38687000000

RBP: ffff923fcf6e3c88 R08: ffff923fcafb0000 R09: 0000000000000000

R10: 0000000000000000 R11: ffffffff83619b90 R12: ffff923fa9540000

R13: 0000000000080007 R14: ffff923f6d35d000 R15: 0000000000000000

FS: 0000000000000000(0000) GS:ffff929d0d7c0000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffe38687000000 CR3: 0000005224c34005 CR4: 0000000000770ee0

PKRU: 55555554

Call Trace:

<TASK>

sev_free_vcpu+0xcb/0x110 [kvm_amd]

svm_vcpu_free+0x75/0xf0 [kvm_amd]

kvm_arch_vcpu_destroy+0x36/0x140 [kvm]

kvm_destroy_vcpus+0x67/0x100 [kvm]

kvm_arch_destroy_vm+0x161/0x1d0 [kvm]

kvm_put_kvm+0x276/0x560 [kvm]

kvm_vm_release+0x25/0x30 [kvm]

__fput+0x106/0x280

____fput+0x12/0x20

task_work_run+0x86/0xb0

do_exit+0x2e3/0x9c0

do_group_exit+0xb1/0xc0

__x64_sys_exit_group+0x1b/0x20

do_syscall_64+0x41/0x90

entry_SYSCALL_64_after_hwframe+0x63/0xcd

</TASK>

CR2: ffffe38687000000