From: Sean Christopherson <seanjc@google.com>
To: Maxim Levitsky <mlevitsk@redhat.com>
Cc: kvm@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
Wanpeng Li <wanpengli@tencent.com>,
Joerg Roedel <joro@8bytes.org>, "H. Peter Anvin" <hpa@zytor.com>,
Jim Mattson <jmattson@google.com>, Ingo Molnar <mingo@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Borislav Petkov <bp@alien8.de>,
"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] KVM: VMX: avoid running vmx_handle_exit_irqoff in case of emulation
Date: Thu, 26 Aug 2021 16:01:06 +0000 [thread overview]
Message-ID: <YSe6wphK9b8KSkXW@google.com> (raw)
In-Reply-To: <20210826095750.1650467-2-mlevitsk@redhat.com>
On Thu, Aug 26, 2021, Maxim Levitsky wrote:
> If we are emulating an invalid guest state, we don't have a correct
> exit reason, and thus we shouldn't do anything in this function.
>
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
This should have Cc: stable. I believe userspace could fairly easily trick KVM
into "handling" a spurious IRQ, e.g. trigger SIGALRM and stuff invalid state.
For all those evil folks running CPUs that are almost old enough to drive :-)
> ---
> arch/x86/kvm/vmx/vmx.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index fada1055f325..0c2c0d5ae873 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6382,6 +6382,9 @@ static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
>
> + if (vmx->emulation_required)
> + return;
Rather than play whack-a-mole with flows consuming stale state, I'd much prefer
to synthesize a VM-Exit(INVALID_GUEST_STATE). Alternatively, just skip ->run()
entirely by adding hooks in vcpu_enter_guest(), but that's a much larger change
and probably not worth the risk at this juncture.
---
arch/x86/kvm/vmx/vmx.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 32e3a8b35b13..12fe63800889 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6618,10 +6618,21 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
vmx->loaded_vmcs->soft_vnmi_blocked))
vmx->loaded_vmcs->entry_time = ktime_get();
- /* Don't enter VMX if guest state is invalid, let the exit handler
- start emulation until we arrive back to a valid state */
- if (vmx->emulation_required)
+ /*
+ * Don't enter VMX if guest state is invalid, let the exit handler
+ * start emulation until we arrive back to a valid state. Synthesize a
+ * consistency check VM-Exit due to invalid guest state and bail.
+ */
+ if (unlikely(vmx->emulation_required)) {
+ vmx->fail = 0;
+ vmx->exit_reason.full = EXIT_REASON_INVALID_STATE;
+ vmx->exit_reason.failed_vmentry = 1;
+ kvm_register_mark_available(vcpu, VCPU_EXREG_EXIT_INFO_1);
+ vmx->exit_qualification = ENTRY_FAIL_DEFAULT;
+ kvm_register_mark_available(vcpu, VCPU_EXREG_EXIT_INFO_2);
+ vmx->exit_intr_info = 0;
return EXIT_FASTPATH_NONE;
+ }
trace_kvm_entry(vcpu);
--
or the beginnings of an aggressive refactor...
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cf8fb6eb676a..a4fe0f78898a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9509,6 +9509,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
goto cancel_injection;
}
+ if (unlikely(static_call(kvm_x86_emulation_required)(vcpu)))
+ return static_call(kvm_x86_emulate_invalid_guest_state)(vcpu);
+
preempt_disable();
static_call(kvm_x86_prepare_guest_switch)(vcpu);
> +
> if (vmx->exit_reason.basic == EXIT_REASON_EXTERNAL_INTERRUPT)
> handle_external_interrupt_irqoff(vcpu);
> else if (vmx->exit_reason.basic == EXIT_REASON_EXCEPTION_NMI)
> --
> 2.26.3
>
next prev parent reply other threads:[~2021-08-26 16:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-26 9:57 [PATCH 0/2] KVM: SMM fixes for nVMX Maxim Levitsky
2021-08-26 9:57 ` [PATCH 1/2] KVM: VMX: avoid running vmx_handle_exit_irqoff in case of emulation Maxim Levitsky
2021-08-26 16:01 ` Sean Christopherson [this message]
2021-08-30 12:27 ` Maxim Levitsky
2021-09-06 10:09 ` Paolo Bonzini
2021-09-06 21:07 ` Maxim Levitsky
2021-09-07 6:50 ` Paolo Bonzini
2021-08-26 9:57 ` [PATCH 2/2] VMX: nSVM: enter protected mode prior to returning to nested guest from SMM Maxim Levitsky
2021-08-26 16:23 ` Sean Christopherson
2021-08-30 12:45 ` Maxim Levitsky
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