Paul Meyer
d76ce200a6
msr() returned 0 on failure, indistinguishable from a real MSR value of
0. With /dev/cpu/0/msr unavailable (e.g. the msr module not loaded in the
initrd), detect_sev() read 0 and reported a genuine SEV/-ES/-SNP guest as
CONFIDENTIAL_VIRTUALIZATION_NONE.
That inverts the firmware-credential trust gate: import_credentials_*()
skip fw_cfg/SMBIOS credentials only when detect_confidential_virtualization()
is > 0 ("don't trust firmware in confidential VMs"). A false NONE makes a
confidential guest trust and import credentials injected by the untrusted
hypervisor.
msr() now returns a negative errno, and detect_sev() assumes plain SEV when
the MSR is unreadable but CPUID already advertised SEV under a hypervisor,
so the gate still trips.
The conservative branch only fires when CPUID already advertised SEV, i.e.
for a guest the hypervisor marked SEV-capable. QEMU gates that CPUID leaf on
the SEV launch object and does not expose it to ordinary guests even under
-cpu host, so it does not misfire for non-confidential guests. Were a
hypervisor to expose the bit anyway the outcome is fail-safe (we only
decline to trust firmware-supplied data); nothing in-tree branches on the
specific SEV tier.
Signed-off-by: Paul Meyer <katexochen0@gmail.com>
System and Service Manager
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