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:

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

---[ end trace 0000000000000000 ]---

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-55881
• https://git.kernel.org/stable/c/0840d360a8909c722fb62459f42836afe32ededb
• https://git.kernel.org/stable/c/22b5c2acd65dbe949032f619d4758a35a82fffc3
• https://git.kernel.org/stable/c/3d2634ec0d1dbe8f4b511cf5261f327c6a76f4b6
• https://git.kernel.org/stable/c/7ed4db315094963de0678a8adfd43c46471b9349
• https://git.kernel.org/stable/c/9b42d1e8e4fe9dc631162c04caa69b0d1860b0f0