Re: [PATCH 8/8] KVM: selftests: nSVM: Add svm_nested_soft_inject_test

Maxim Levitsky
2022-04-04T12:27:54Z

On Sat, 2022-04-02 at 01:09 +0000, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
>
> Add a KVM self-test that checks whether a nSVM L1 is able to successfully
> inject a software interrupt and a soft exception into its L2 guest.
>
> In practice, this tests both the next_rip field consistency and
> L1-injected event with intervening L0 VMEXIT during its delivery:
> the first nested VMRUN (that's also trying to inject a software interrupt)
> will immediately trigger a L0 NPF.
> This L0 NPF will have zero in its CPU-returned next_rip field, which if
> incorrectly reused by KVM will trigger a #PF when trying to return to
> such address 0 from the interrupt handler.
>
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> tools/testing/selftests/kvm/.gitignore | 1 +
> tools/testing/selftests/kvm/Makefile | 1 +
> .../selftests/kvm/include/x86_64/svm_util.h | 2 +
> .../kvm/x86_64/svm_nested_soft_inject_test.c | 147 ++++++++++++++++++
> 4 files changed, 151 insertions(+)
> create mode 100644 tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c
>
> diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
> index 1f1b6c978bf7..1354d3f4a362 100644
> --- a/tools/testing/selftests/kvm/.gitignore
> +++ b/tools/testing/selftests/kvm/.gitignore
> @@ -33,6 +33,7 @@
> /x86_64/state_test
> /x86_64/svm_vmcall_test
> /x86_64/svm_int_ctl_test
> +/x86_64/svm_nested_soft_inject_test
> /x86_64/sync_regs_test
> /x86_64/tsc_msrs_test
> /x86_64/userspace_io_test
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index c9cdbd248727..cef6d583044b 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -66,6 +66,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/state_test
> TEST_GEN_PROGS_x86_64 += x86_64/vmx_preemption_timer_test
> TEST_GEN_PROGS_x86_64 += x86_64/svm_vmcall_test
> TEST_GEN_PROGS_x86_64 += x86_64/svm_int_ctl_test
> +TEST_GEN_PROGS_x86_64 += x86_64/svm_nested_soft_inject_test
> TEST_GEN_PROGS_x86_64 += x86_64/tsc_scaling_sync
> TEST_GEN_PROGS_x86_64 += x86_64/sync_regs_test
> TEST_GEN_PROGS_x86_64 += x86_64/userspace_io_test
> diff --git a/tools/testing/selftests/kvm/include/x86_64/svm_util.h b/tools/testing/selftests/kvm/include/x86_64/svm_util.h
> index a25aabd8f5e7..d49f7c9b4564 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/svm_util.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/svm_util.h
> @@ -16,6 +16,8 @@
> #define CPUID_SVM_BIT 2
> #define CPUID_SVM BIT_ULL(CPUID_SVM_BIT)
>
> +#define SVM_EXIT_EXCP_BASE 0x040
> +#define SVM_EXIT_HLT 0x078
> #define SVM_EXIT_MSR 0x07c
> #define SVM_EXIT_VMMCALL 0x081
>
> diff --git a/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c b/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c
> new file mode 100644
> index 000000000000..d39be5d885c1
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/x86_64/svm_nested_soft_inject_test.c
> @@ -0,0 +1,147 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2022 Oracle and/or its affiliates.
> + *
> + * Based on:
> + * svm_int_ctl_test
> + *
> + * Copyright (C) 2021, Red Hat, Inc.
> + *
> + */
> +
> +#include "test_util.h"
> +#include "kvm_util.h"
> +#include "processor.h"
> +#include "svm_util.h"
> +
> +#define VCPU_ID 0
> +#define INT_NR 0x20
> +#define X86_FEATURE_NRIPS BIT(3)
> +
> +#define vmcall() \
> + __asm__ __volatile__( \
> + "vmmcall\n" \
> + )
> +
> +#define ud2() \
> + __asm__ __volatile__( \
> + "ud2\n" \
> + )
> +
> +#define hlt() \
> + __asm__ __volatile__( \
> + "hlt\n" \
> + )

Minor nitpick: I guess it would be nice to put these in some common header file.

> +
> +static unsigned int bp_fired;
> +static void guest_bp_handler(struct ex_regs *regs)
> +{
> + bp_fired++;
> +}
> +
> +static unsigned int int_fired;
> +static void guest_int_handler(struct ex_regs *regs)
> +{
> + int_fired++;
> +}
> +
> +static void l2_guest_code(void)
> +{
> + GUEST_ASSERT(int_fired == 1);
> + vmcall();
> + ud2();
> +
> + GUEST_ASSERT(bp_fired == 1);
> + hlt();
> +}

Yes, I was right - the test indeed has no either INT 0x20 nor INT 3 in the L2 guest code,
and yet this should work.

> +
> +static void l1_guest_code(struct svm_test_data *svm)
> +{
> + #define L2_GUEST_STACK_SIZE 64
> + unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
> + struct vmcb *vmcb = svm->vmcb;
> +
> + /* Prepare for L2 execution. */
> + generic_svm_setup(svm, l2_guest_code,
> + &l2_guest_stack[L2_GUEST_STACK_SIZE]);
> +
> + vmcb->control.intercept_exceptions |= BIT(PF_VECTOR) | BIT(UD_VECTOR);
> + vmcb->control.intercept |= BIT(INTERCEPT_HLT);
> +
> + vmcb->control.event_inj = INT_NR | SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_SOFT;
> + /* The return address pushed on stack */
> + vmcb->control.next_rip = vmcb->save.rip;

I'll would be putting even something more spicy here just to see that KVM preserves this field
like say put two ud2 in the start of guest code, and here have

vmcb->control.next_rip = vmcb->save.rip + 4; // skip over two ud2 instructions.

That way KVM won't be able to skip over a single instruction to get correct next_rip

> +
> + run_guest(vmcb, svm->vmcb_gpa);
> + GUEST_ASSERT_3(vmcb->control.exit_code == SVM_EXIT_VMMCALL,
> + vmcb->control.exit_code,
> + vmcb->control.exit_info_1, vmcb->control.exit_info_2);
> +
> + /* Skip over VMCALL */
> + vmcb->save.rip += 3;
> +
> + vmcb->control.event_inj = BP_VECTOR | SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_EXEPT;
> + /* The return address pushed on stack, skip over UD2 */
> + vmcb->control.next_rip = vmcb->save.rip + 2;
> +
> + run_guest(vmcb, svm->vmcb_gpa);
> + GUEST_ASSERT_3(vmcb->control.exit_code == SVM_EXIT_HLT,
> + vmcb->control.exit_code,
> + vmcb->control.exit_info_1, vmcb->control.exit_info_2);
> +
> + GUEST_DONE();
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + struct kvm_cpuid_entry2 *cpuid;
> + struct kvm_vm *vm;
> + vm_vaddr_t svm_gva;
> + struct kvm_guest_debug debug;
> +
> + nested_svm_check_supported();
> +
> + cpuid = kvm_get_supported_cpuid_entry(0x8000000a);
> + if (!(cpuid->edx & X86_FEATURE_NRIPS)) {
> + print_skip("nRIP Save unavailable");
> + exit(KSFT_SKIP);
> + }
> +
> + vm = vm_create_default(VCPU_ID, 0, (void *) l1_guest_code);
> +
> + vm_init_descriptor_tables(vm);
> + vcpu_init_descriptor_tables(vm, VCPU_ID);
> +
> + vm_install_exception_handler(vm, BP_VECTOR, guest_bp_handler);
> + vm_install_exception_handler(vm, INT_NR, guest_int_handler);
> +
> + vcpu_alloc_svm(vm, &svm_gva);
> + vcpu_args_set(vm, VCPU_ID, 1, svm_gva);
> +
> + memset(&debug, 0, sizeof(debug));
> + vcpu_set_guest_debug(vm, VCPU_ID, &debug);
> +
> + struct kvm_run *run = vcpu_state(vm, VCPU_ID);
> + struct ucall uc;
> +
> + vcpu_run(vm, VCPU_ID);
> + TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
> + "Got exit_reason other than KVM_EXIT_IO: %u (%s)\n",
> + run->exit_reason,
> + exit_reason_str(run->exit_reason));
> +
> + switch (get_ucall(vm, VCPU_ID, &uc)) {
> + case UCALL_ABORT:
> + TEST_FAIL("%s at %s:%ld, vals = 0x%lx 0x%lx 0x%lx", (const char *)uc.args[0],
> + __FILE__, uc.args[1], uc.args[2], uc.args[3], uc.args[4]);
> + break;
> + /* NOT REACHED */
> + case UCALL_DONE:
> + goto done;
> + default:
> + TEST_FAIL("Unknown ucall 0x%lx.", uc.cmd);
> + }
> +done:
> + kvm_vm_free(vm);
> + return 0;
> +}

Other that nitpicks:

Reviewed-by: Maxim levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky