[v3,0/4] Relax canonical checks on some arch msrs

Message

Maxim Levitsky Aug. 15, 2024, 12:33 p.m. UTC

Recently we came up upon a failure where likely the guest writes
0xff4547ceb1600000 to MSR_KERNEL_GS_BASE and later on, qemu
sets this value via KVM_PUT_MSRS, and is rejected by the
kernel, likely due to not being canonical in 4 level paging.

One of the way to trigger this is to make the guest enter SMM,
which causes paging to be disabled, which SMM bios re-enables
but not the whole 5 level. MSR_KERNEL_GS_BASE on the other
hand continues to contain old value.

I did some reverse engineering and to my surprise I found out
that both Intel and AMD indeed ignore CR4.LA57 when doing
canonical checks on this and other msrs and/or other arch
registers (like GDT base) which contain linear addresses.

V2: addressed a very good feedback from Chao Gao. Thanks!

V3: also fix the nested VMX, and also fix the
MSR_IA32_SYSENTER_EIP / MSR_IA32_SYSENTER_ESP

Best regards,
	Maxim Levitsky

Maxim Levitsky (4):
  KVM: x86: relax canonical check for some x86 architectural msrs
  KVM: x86: add X86_FEATURE_LA57 to governed_features
  KVM: nVMX: relax canonical checks on some x86 registers in vmx host
    state
  KVM: SVM: fix emulation of msr reads/writes of MSR_FS_BASE and
    MSR_GS_BASE

 arch/x86/kvm/cpuid.c             |  2 ++
 arch/x86/kvm/governed_features.h |  1 +
 arch/x86/kvm/svm/svm.c           | 12 ++++++++++++
 arch/x86/kvm/vmx/nested.c        | 30 +++++++++++++++++++++++-------
 arch/x86/kvm/x86.c               | 29 +++++++++++++++++++++++++++--
 5 files changed, 65 insertions(+), 9 deletions(-)