KVM: x86: Play nice with protected guests in complete_hypercall_exit()

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

KVM: x86: Play nice with protected guests in complete_hypercall_exit()

Use is_64_bit_hypercall() instead of is_64_bit_mode() to detect a 64-bit

hypercall when completing said hypercall. For guests with protected state,

e.g. SEV-ES and SEV-SNP, KVM must assume the hypercall was made in 64-bit

mode as the vCPU state needed to detect 64-bit mode is unavailable.

Hacking the sev_smoke_test selftest to generate a KVM_HC_MAP_GPA_RANGE

hypercall via VMGEXIT trips the WARN:

------------[ cut here ]------------

WARNING: CPU: 273 PID: 326626 at arch/x86/kvm/x86.h:180 complete_hypercall_exit+0x44/0xe0 [kvm]

Modules linked in: kvm_amd kvm ... [last unloaded: kvm]

CPU: 273 UID: 0 PID: 326626 Comm: sev_smoke_test Not tainted 6.12.0-smp--392e932fa0f3-feat #470

Hardware name: Google Astoria/astoria, BIOS 0.20240617.0-0 06/17/2024

RIP: 0010:complete_hypercall_exit+0x44/0xe0 [kvm]

Call Trace:

<TASK>

kvm_arch_vcpu_ioctl_run+0x2400/0x2720 [kvm]

kvm_vcpu_ioctl+0x54f/0x630 [kvm]

__se_sys_ioctl+0x6b/0xc0

do_syscall_64+0x83/0x160

entry_SYSCALL_64_after_hwframe+0x76/0x7e

</TASK>

---[ end trace 0000000000000000 ]---