CVE-2024-55881

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References