CVE-2024-55881: KVM: x86: Play nice with protected guests in complete_hypercall_exit()

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-01-11 · updated 2026-06-17

Description

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 ]---

Affected products

Linux kernel: from 5.15.5 before 5.15.176; from 5.16.1 before 6.1.122; from 6.2 before 6.6.68; from 6.7 before 6.12.7; 5.16, 5.16-rc2, 5.16-rc3, 5.16-rc4, 5.16-rc5, 5.16-rc6 (+5) — fixed in 5.15.176, 6.1.122, 6.12.7, 6.6.68

How to fix

Upgrade to a fixed version: Linux kernel 5.15.176, 6.1.122, 6.12.7, 6.6.68. Check the vendor advisory for mitigations.

References

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