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Date: Tue, 14 Dec 2021 11:15:32 +0200
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
syzbot+f1d2136db9c80d4733e8@...kaller.appspotmail.com
Subject: Re: [PATCH 4/4] KVM: selftests: Add test to verify TRIPLE_FAULT on
invalid L2 guest state
On Tue, 2021-12-07 at 19:30 +0000, Sean Christopherson wrote:
> Add a selftest to attempt to enter L2 with invalid guests state by
> exiting to userspace via I/O from L2, and then using KVM_SET_SREGS to set
> invalid guest state (marking TR unusable is arbitrary chosen for its
> relative simplicity).
>
> This is a regression test for a bug introduced by commit c8607e4a086f
> ("KVM: x86: nVMX: don't fail nested VM entry on invalid guest state if
> !from_vmentry"), which incorrectly set vmx->fail=true when L2 had invalid
> guest state and ultimately triggered a WARN due to nested_vmx_vmexit()
> seeing vmx->fail==true while attempting to synthesize a nested VM-Exit.
>
> The is also a functional test to verify that KVM sythesizes TRIPLE_FAULT
> for L2, which is somewhat arbitrary behavior, instead of emulating L2.
> KVM should never emulate L2 due to invalid guest state, as it's
> architecturally impossible for L1 to run an L2 guest with invalid state
> as nested VM-Enter should always fail, i.e. L1 needs to do the emulation.
> Stuffing state via KVM ioctl() is a non-architctural, out-of-band case,
> hence the TRIPLE_FAULT being rather arbitrary.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> tools/testing/selftests/kvm/.gitignore | 1 +
> tools/testing/selftests/kvm/Makefile | 1 +
> .../x86_64/vmx_invalid_nested_guest_state.c | 105 ++++++++++++++++++
> 3 files changed, 107 insertions(+)
> create mode 100644 tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c
>
> diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
> index 3763105029fb..de41afb01a77 100644
> --- a/tools/testing/selftests/kvm/.gitignore
> +++ b/tools/testing/selftests/kvm/.gitignore
> @@ -34,6 +34,7 @@
> /x86_64/vmx_apic_access_test
> /x86_64/vmx_close_while_nested_test
> /x86_64/vmx_dirty_log_test
> +/x86_64/vmx_invalid_nested_guest_state
> /x86_64/vmx_preemption_timer_test
> /x86_64/vmx_set_nested_state_test
> /x86_64/vmx_tsc_adjust_test
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index c4e34717826a..6be4144c8d25 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -63,6 +63,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/userspace_msr_exit_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_apic_access_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_close_while_nested_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_dirty_log_test
> +TEST_GEN_PROGS_x86_64 += x86_64/vmx_invalid_nested_guest_state
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_nested_tsc_scaling_test
> diff --git a/tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c b/tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c
> new file mode 100644
> index 000000000000..489fbed4ca6f
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/vmx_invalid_nested_guest_state.c
> @@ -0,0 +1,105 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include "test_util.h"
> +#include "kvm_util.h"
> +#include "processor.h"
> +#include "vmx.h"
> +
> +#include <string.h>
> +#include <sys/ioctl.h>
> +
> +#include "kselftest.h"
> +
> +#define VCPU_ID 0
> +#define ARBITRARY_IO_PORT 0x2000
> +
> +static struct kvm_vm *vm;
> +
> +static void l2_guest_code(void)
> +{
> + /*
> + * Generate an exit to L0 userspace, i.e. main(), via I/O to an
> + * arbitrary port.
> + */
> + asm volatile("inb %%dx, %%al"
> + : : [port] "d" (ARBITRARY_IO_PORT) : "rax");
> +}
> +
> +static void l1_guest_code(struct vmx_pages *vmx_pages)
> +{
> +#define L2_GUEST_STACK_SIZE 64
> + unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
> +
> + GUEST_ASSERT(prepare_for_vmx_operation(vmx_pages));
> + GUEST_ASSERT(load_vmcs(vmx_pages));
> +
> + /* Prepare the VMCS for L2 execution. */
> + prepare_vmcs(vmx_pages, l2_guest_code,
> + &l2_guest_stack[L2_GUEST_STACK_SIZE]);
> +
> + /*
> + * L2 must be run without unrestricted guest, verify that the selftests
> + * library hasn't enabled it. Because KVM selftests jump directly to
> + * 64-bit mode, unrestricted guest support isn't required.
> + */
> + GUEST_ASSERT(!(vmreadz(CPU_BASED_VM_EXEC_CONTROL) & CPU_BASED_ACTIVATE_SECONDARY_CONTROLS) ||
> + !(vmreadz(SECONDARY_VM_EXEC_CONTROL) & SECONDARY_EXEC_UNRESTRICTED_GUEST));
> +
> + GUEST_ASSERT(!vmlaunch());
> +
> + /* L2 should triple fault after main() stuffs invalid guest state. */
> + GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_TRIPLE_FAULT);
> + GUEST_DONE();
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + vm_vaddr_t vmx_pages_gva;
> + struct kvm_sregs sregs;
> + struct kvm_run *run;
> + struct ucall uc;
> +
> + nested_vmx_check_supported();
> +
> + vm = vm_create_default(VCPU_ID, 0, (void *) l1_guest_code);
> +
> + /* Allocate VMX pages and shared descriptors (vmx_pages). */
> + vcpu_alloc_vmx(vm, &vmx_pages_gva);
> + vcpu_args_set(vm, VCPU_ID, 1, vmx_pages_gva);
> +
> + vcpu_run(vm, VCPU_ID);
> +
> + run = vcpu_state(vm, VCPU_ID);
> +
> + /*
> + * The first exit to L0 userspace should be an I/O access from L2.
> + * Running L1 should launch L2 without triggering an exit to userspace.
> + */
> + TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
> + "Expected KVM_EXIT_IO, got: %u (%s)\n",
> + run->exit_reason, exit_reason_str(run->exit_reason));
> +
> + TEST_ASSERT(run->io.port == ARBITRARY_IO_PORT,
> + "Expected IN from port %d from L2, got port %d",
> + ARBITRARY_IO_PORT, run->io.port);
> +
> + /*
> + * Stuff invalid guest state for L2 by making TR unusuable. The next
> + * KVM_RUN should induce a TRIPLE_FAULT in L2 as KVM doesn't support
> + * emulating invalid guest state for L2.
> + */
> + memset(&sregs, 0, sizeof(sregs));
> + vcpu_sregs_get(vm, VCPU_ID, &sregs);
> + sregs.tr.unusable = 1;
> + vcpu_sregs_set(vm, VCPU_ID, &sregs);
> +
> + vcpu_run(vm, VCPU_ID);
> +
> + switch (get_ucall(vm, VCPU_ID, &uc)) {
> + case UCALL_DONE:
> + break;
> + case UCALL_ABORT:
> + TEST_FAIL("%s", (const char *)uc.args[0]);
> + default:
> + TEST_FAIL("Unexpected ucall: %lu", uc.cmd);
> + }
> +}
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Best regards,
Maxim Levitsky
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