Fix a (VMX only) bug reported by Maxim where KVM caches a stale SS.AR_BYTES when involuntary preemption schedules out a vCPU during vmx_vcpu_rest(), and ultimately clobbers the VMCS's SS.AR_BYTES if userspace does KVM_GET_SREGS => KVM_SET_SREGS, i.e. if userspace writes the stale value back into KVM. v4, as this is a spiritual successor to Maxim's earlier series. Patch 1 fixes the underlying problem by avoiding the cache in kvm_sched_out(). Patch 2 fixes vmx_vcpu_reset() to invalidate the cache _after_ writing the VMCS, which also fixes the VMCS clobbering bug, but isn't as robust of a fix for KVM as a whole, e.g. any other flow that invalidates the cache too "early" would be susceptible to the bug, and on its own doesn't allow for the hardening in patch 3. Patch 3 hardens KVM against using the register caches from !TASK context. Except for PMI callbacks, which are tightly bounded, i.e. can't run while KVM is modifying segment information, using the register caches from IRQ/NMI is unsafe. Patch 4 is a tangentially related cleanup. v3: https://lore.kernel.org/all/20240725175232.337266-1-mlevitsk@xxxxxxxxxx Maxim Levitsky (1): KVM: VMX: reset the segment cache after segment init in vmx_vcpu_reset() Sean Christopherson (3): KVM: x86: Bypass register cache when querying CPL from kvm_sched_out() KVM: x86: Add lockdep-guarded asserts on register cache usage KVM: x86: Use '0' for guest RIP if PMI encounters protected guest state arch/x86/include/asm/kvm-x86-ops.h | 1 + arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/kvm_cache_regs.h | 17 +++++++++++++++++ arch/x86/kvm/svm/svm.c | 1 + arch/x86/kvm/vmx/main.c | 1 + arch/x86/kvm/vmx/vmx.c | 29 +++++++++++++++++++++-------- arch/x86/kvm/vmx/vmx.h | 1 + arch/x86/kvm/x86.c | 15 ++++++++++++++- 8 files changed, 57 insertions(+), 9 deletions(-) base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b -- 2.47.0.rc1.288.g06298d1525-goog
