Commit f244deed authored Jul 20, 2017 by Wanpeng Li Committed by Radim Krčmář Jul 20, 2017

KVM: VMX: Fix invalid guest state detection after task-switch emulation



This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y
or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries
to emulate invalid guest state task-switch:

kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
kvm_emulate_insn: 42000:0:0f 0b (0x2)
kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
kvm_inj_exception: #UD (0x0)
kvm_entry: vcpu 0
kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0
kvm_emulate_insn: 42000:0:0f 0b (0x2)
kvm_emulate_insn: 42000:0:0f 0b (0x2) failed
kvm_inj_exception: #UD (0x0)
......................

It appears that the task-switch emulation updates rflags (and vm86
flag) only after the segments are loaded, causing vmx->emulation_required
to be set, when in fact invalid guest state emulation is not needed.

This patch fixes it by updating vmx->emulation_required after the
rflags (and vm86 flag) is updated in task-switch emulation.

Thanks Radim for moving the update to vmx__set_flags and adding Paolo's
suggestion for the check.

Suggested-by: Nadav Amit <nadav.amit@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

parent c2ce3f5d

arch/x86/kvm/vmx.c

+10 −5

Original line number	Diff line number	Diff line
		@@ -2327,6 +2327,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
		__vmx_load_host_state(to_vmx(vcpu));
		}

		static bool emulation_required(struct kvm_vcpu *vcpu)
		{
		return emulate_invalid_guest_state && !guest_state_valid(vcpu);
		}

		static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);

		/*
		@@ -2364,6 +2369,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)

		static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
		{
		unsigned long old_rflags = vmx_get_rflags(vcpu);

		__set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
		to_vmx(vcpu)->rflags = rflags;
		if (to_vmx(vcpu)->rmode.vm86_active) {
		@@ -2371,6 +2378,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
		rflags \|= X86_EFLAGS_IOPL \| X86_EFLAGS_VM;
		}
		vmcs_writel(GUEST_RFLAGS, rflags);

		if ((old_rflags ^ to_vmx(vcpu)->rflags) & X86_EFLAGS_VM)
		to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
		}

		static u32 vmx_get_pkru(struct kvm_vcpu *vcpu)
		@@ -3858,11 +3868,6 @@ static __init int alloc_kvm_area(void)
		return 0;
		}

		static bool emulation_required(struct kvm_vcpu *vcpu)
		{
		return emulate_invalid_guest_state && !guest_state_valid(vcpu);
		}

		static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
		struct kvm_segment *save)
		{

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