[PATCH v3 0/3] KVM: SEV-ES: Fix KVM_{GET|SET}_MSRS and LBRV handling

Ravi Bangoria
2024-05-23T12:19:08Z

Fix couple of interrelated issues:

o KVM currently allows userspace to access MSRs even after the VMSA is
encrypted. This can result into issues if MSR update has side effects on
VM configuration. Patch 1 fixes that by preventing KVM_{GET|SET}_MSRS
for SEV-ES guests once VMSA is encrypted.

o As documented in APM, LBR Virtualization must be enabled for SEV-ES
guests. However, KVM currently enables LBRV unconditionally without
checking feature bit, which is wrong. Patch 2 prevents SEV-ES guests
when LBRV support is missing.

o Although LBRV is enabled for SEV-ES guests, MSR_IA32_DEBUGCTLMSR was
still intercepted. This can crash SEV-ES guest if used inadvertently.
Patch 3 fixes it.

Patches prepared on kvm/next (6f627b425378)

v2: https://lore.kernel.org/r/20240416050338.517-1-ravi.bangoria@amd.com
v2->v3: Fix all affiliated issues along with fixing MSR_IA32_DEBUGCTLMSR
interception:
- Block KVM_{GET|SET}_MSRS for SEV-ES guests post VMSA encryption (new)
- Block SEV-ES guest creation when LBRV is disabled/not supported (new)
- Move LBRV enablement code after VMSA encryption to avoid a scenario
where LBRV can be disabled inadvertently through MSR_IA32_DEBUGCTLMSR
write. (new)
- Removed all 'Reviewed-by' since the code has changed quite a bit.

Nikunj A Dadhania (1):
KVM: SEV-ES: Prevent MSR access post VMSA encryption

Ravi Bangoria (2):
KVM: SEV-ES: Disallow SEV-ES guests when X86_FEATURE_LBRV is absent
KVM: SEV-ES: Fix LBRV code

arch/x86/kvm/svm/sev.c | 21 +++++++++++++++------
arch/x86/kvm/svm/svm.c | 42 ++++++++++++++++++++++++++++++++----------
arch/x86/kvm/svm/svm.h | 7 ++++---
3 files changed, 51 insertions(+), 19 deletions(-)

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2.45.1