Yell loudly if KVM attempts to load CS outside of Real Mode without an accompanying control transfer type, i.e. on X86_TRANSFER_NONE. KVM uses X86_TRANSFER_NONE when emulating IRET and exceptions/interrupts for Real Mode, but IRET emulation for Protected Mode is non-existent. WARN instead of trying to pass in a less-wrong type, e.g. X86_TRANSFER_RET, as emulating IRET goes even beyond emulating FAR RET (which KVM also doesn't fully support). Reported-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/emulate.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index baf97c56aefa..07e5f473f6fe 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1640,6 +1640,14 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt, goto exception; break; case VCPU_SREG_CS: + /* + * KVM uses "none" when loading CS as part of emulating Real + * Mode exceptions and IRET (handled above). In all other + * cases, loading CS without a control transfer is a KVM bug. + */ + if (WARN_ON_ONCE(transfer == X86_TRANSFER_NONE)) + goto exception; + if (!(seg_desc.type & 8)) goto exception; base-commit: 62ef199250cd46fb66fe98267137b7f64e0b41b4 -- 2.39.2.637.g21b0678d19-goog
