CVE-2024-55881

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

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

Use is64bithypercall() instead of is64bitmode() 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 sevsmoketest selftest to generate a KVMHCMAPGPARANGE hypercall via VMGEXIT trips the WARN:

------------[ cut here ]------------ WARNING: CPU: 273 PID: 326626 at arch/x86/kvm/x86.h:180 completehypercallexit+0x44/0xe0 [kvm] Modules linked in: kvmamd kvm ... [last unloaded: kvm] CPU: 273 UID: 0 PID: 326626 Comm: sevsmoketest Not tainted 6.12.0-smp--392e932fa0f3-feat #470 Hardware name: Google Astoria/astoria, BIOS 0.20240617.0-0 06/17/2024 RIP: 0010:completehypercallexit+0x44/0xe0 [kvm] Call Trace: <TASK> kvmarchvcpuioctlrun+0x2400/0x2720 [kvm] kvmvcpuioctl+0x54f/0x630 [kvm] _sesysioctl+0x6b/0xc0 dosyscall64+0x83/0x160 entrySYSCALL64afterhwframe+0x76/0x7e </TASK> ---[ end trace 0000000000000000 ]---