[PATCH 0/2] KVM: x86: Syzkaller nested_run_pending defense

[Sean Christopherson]

Defeat syzkaller once and for all when it comes to nested_run_pending (yeah,
those words won't come back to haunt me), by treating nested_run_pending as
"untrusted" for the purposes of WARNs if userspace gains control of the vCPU.
I.e. don't WARN if userspace _may_ have stuffed vCPU state to force an
impossible VM-Exit.

We've reached the point where the signal:noise ratio for nested_run_pending
WARNs when syzkaller is fuzzing nVMX/nSVM is awful, and playing whack-a-mole
with syzkaller is doing more harm that good at this point.  While it's
possible syzkaller could find an actual KVM bug by stuffing vCPU state, if the
_only_ symptom is the nested_run_pending WARN, then in theory the bug should
also be hittable by stuffing L2 state prior to nested VM-Enter.

Sean Christopherson (1):
  KVM: x86: Suppress WARNs on nested_run_pending after userspace exit

Yosry Ahmed (1):
  KVM: x86: Move nested_run_pending to kvm_vcpu_arch

 arch/x86/include/asm/kvm_host.h | 15 ++++++++++
 arch/x86/kvm/svm/nested.c       | 23 ++++++++-------
 arch/x86/kvm/svm/svm.c          | 16 +++++------
 arch/x86/kvm/svm/svm.h          |  4 ---
 arch/x86/kvm/vmx/nested.c       | 50 +++++++++++++++++----------------
 arch/x86/kvm/vmx/vmx.c          | 16 +++++------
 arch/x86/kvm/vmx/vmx.h          |  3 --
 arch/x86/kvm/x86.c              |  7 +++++
 arch/x86/kvm/x86.h              | 10 +++++++
 9 files changed, 87 insertions(+), 57 deletions(-)


base-commit: 5128b972fb2801ad9aca54d990a75611ab5283a9
-- 
2.53.0.473.g4a7958ca14-goog