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    Subject[PATCH 5.19 0590/1157] KVM: SVM: Unwind "speculative" RIP advancement if INTn injection "fails"
    Date
    From: Sean Christopherson <seanjc@google.com>

    [ Upstream commit cd9e6da8048c5b40315ee2d929b6230ce1252c3c ]

    Unwind the RIP advancement done by svm_queue_exception() when injecting
    an INT3 ultimately "fails" due to the CPU encountering a VM-Exit while
    vectoring the injected event, even if the exception reported by the CPU
    isn't the same event that was injected. If vectoring INT3 encounters an
    exception, e.g. #NP, and vectoring the #NP encounters an intercepted
    exception, e.g. #PF when KVM is using shadow paging, then the #NP will
    be reported as the event that was in-progress.

    Note, this is still imperfect, as it will get a false positive if the
    INT3 is cleanly injected, no VM-Exit occurs before the IRET from the INT3
    handler in the guest, the instruction following the INT3 generates an
    exception (directly or indirectly), _and_ vectoring that exception
    encounters an exception that is intercepted by KVM. The false positives
    could theoretically be solved by further analyzing the vectoring event,
    e.g. by comparing the error code against the expected error code were an
    exception to occur when vectoring the original injected exception, but
    SVM without NRIPS is a complete disaster, trying to make it 100% correct
    is a waste of time.

    Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
    Fixes: 66b7138f9136 ("KVM: SVM: Emulate nRIP feature when reinjecting INT3")
    Signed-off-by: Sean Christopherson <seanjc@google.com>
    Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
    Message-Id: <450133cf0a026cb9825a2ff55d02cb136a1cb111.1651440202.git.maciej.szmigiero@oracle.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kvm/svm/svm.c | 23 +++++++++++++++--------
    1 file changed, 15 insertions(+), 8 deletions(-)

    diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
    index 40e560c875f1..fe8536c57fd7 100644
    --- a/arch/x86/kvm/svm/svm.c
    +++ b/arch/x86/kvm/svm/svm.c
    @@ -3699,6 +3699,18 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
    vector = exitintinfo & SVM_EXITINTINFO_VEC_MASK;
    type = exitintinfo & SVM_EXITINTINFO_TYPE_MASK;

    + /*
    + * If NextRIP isn't enabled, KVM must manually advance RIP prior to
    + * injecting the soft exception/interrupt. That advancement needs to
    + * be unwound if vectoring didn't complete. Note, the _new_ event may
    + * not be the injected event, e.g. if KVM injected an INTn, the INTn
    + * hit a #NP in the guest, and the #NP encountered a #PF, the #NP will
    + * be the reported vectored event, but RIP still needs to be unwound.
    + */
    + if (int3_injected && type == SVM_EXITINTINFO_TYPE_EXEPT &&
    + kvm_is_linear_rip(vcpu, svm->int3_rip))
    + kvm_rip_write(vcpu, kvm_rip_read(vcpu) - int3_injected);
    +
    switch (type) {
    case SVM_EXITINTINFO_TYPE_NMI:
    vcpu->arch.nmi_injected = true;
    @@ -3712,16 +3724,11 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)

    /*
    * In case of software exceptions, do not reinject the vector,
    - * but re-execute the instruction instead. Rewind RIP first
    - * if we emulated INT3 before.
    + * but re-execute the instruction instead.
    */
    - if (kvm_exception_is_soft(vector)) {
    - if (vector == BP_VECTOR && int3_injected &&
    - kvm_is_linear_rip(vcpu, svm->int3_rip))
    - kvm_rip_write(vcpu,
    - kvm_rip_read(vcpu) - int3_injected);
    + if (kvm_exception_is_soft(vector))
    break;
    - }
    +
    if (exitintinfo & SVM_EXITINTINFO_VALID_ERR) {
    u32 err = svm->vmcb->control.exit_int_info_err;
    kvm_requeue_exception_e(vcpu, vector, err);
    --
    2.35.1


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