[PATCH 21/21] KVM: selftests: Add an x86-only test to verify nested exception queueing

Sean Christopherson
2022-03-11T03:30:02Z

Add a test to verify that KVM_{G,S}ET_EVENTS play nice with pending vs.
injected exceptions when an exception is being queued for L2, and that
KVM correctly handles L1's exception intercept wants.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
tools/testing/selftests/kvm/.gitignore | 1 +
tools/testing/selftests/kvm/Makefile | 1 +
.../kvm/x86_64/nested_exceptions_test.c | 307 ++++++++++++++++++
3 files changed, 309 insertions(+)
create mode 100644 tools/testing/selftests/kvm/x86_64/nested_exceptions_test.c

diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
index 9b67343dc4ab..c8b8203ca867 100644
--- a/tools/testing/selftests/kvm/.gitignore
+++ b/tools/testing/selftests/kvm/.gitignore
@@ -23,6 +23,7 @@
/x86_64/hyperv_features
/x86_64/mmio_warning_test
/x86_64/mmu_role_test
+/x86_64/nested_exceptions_test
/x86_64/platform_info_test
/x86_64/pmu_event_filter_test
/x86_64/set_boot_cpu_id
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 04099f453b59..5679d1a79a83 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -56,6 +56,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/kvm_clock_test
TEST_GEN_PROGS_x86_64 += x86_64/kvm_pv_test
TEST_GEN_PROGS_x86_64 += x86_64/mmio_warning_test
TEST_GEN_PROGS_x86_64 += x86_64/mmu_role_test
+TEST_GEN_PROGS_x86_64 += x86_64/nested_exceptions_test
TEST_GEN_PROGS_x86_64 += x86_64/platform_info_test
TEST_GEN_PROGS_x86_64 += x86_64/pmu_event_filter_test
TEST_GEN_PROGS_x86_64 += x86_64/set_boot_cpu_id
diff --git a/tools/testing/selftests/kvm/x86_64/nested_exceptions_test.c b/tools/testing/selftests/kvm/x86_64/nested_exceptions_test.c
new file mode 100644
index 000000000000..1a2b2010e8f3
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/nested_exceptions_test.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define _GNU_SOURCE /* for program_invocation_short_name */
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+#include "vmx.h"
+#include "svm_util.h"
+
+#define VCPU_ID 0
+#define L2_GUEST_STACK_SIZE 256
+
+/*
+ * Arbitrary, never shoved into KVM/hardware, just need to avoid conflict with
+ * the "real" exceptions used, #SS/#GP/#DF (12/13/8).
+ */
+#define FAKE_TRIPLE_FAULT_VECTOR 0xaa
+
+/* Arbitrary 32-bit error code injected by this test. */
+#define SS_ERROR_CODE 0xdeadbeef
+
+/*
+ * Bit '0' is set on Intel if the exception occurs while delivering a previous
+ * event/exception. AMD's wording is ambiguous, but presumably the bit is set
+ * if the exception occurs while delivering an external event, e.g. NMI or INTR,
+ * but not for exceptions that occur when delivering other exceptions or
+ * software interrupts.
+ *
+ * Note, Intel's name for it, "External event", is misleading and much more
+ * aligned with AMD's behavior, but the SDM is quite clear on its behavior.
+ */
+#define ERROR_CODE_EXT_FLAG BIT(0)
+
+/*
+ * Bit '1' is set if the fault occurred when looking up a descriptor in the
+ * IDT, which is the case here as the IDT is empty/NULL.
+ */
+#define ERROR_CODE_IDT_FLAG BIT(1)
+
+/*
+ * The #GP that occurs when vectoring #SS should show the index into the IDT
+ * for #SS, plus have the "IDT flag" set.
+ */
+#define GP_ERROR_CODE_AMD ((SS_VECTOR * 8) | ERROR_CODE_IDT_FLAG)
+#define GP_ERROR_CODE_INTEL ((SS_VECTOR * 8) | ERROR_CODE_IDT_FLAG | ERROR_CODE_EXT_FLAG)
+
+/*
+ * Intel and AMD both shove '0' into the error code on #DF, regardless of what
+ * led to the double fault.
+ */
+#define DF_ERROR_CODE 0
+
+#define INTERCEPT_SS (BIT_ULL(SS_VECTOR))
+#define INTERCEPT_SS_DF (INTERCEPT_SS | BIT_ULL(DF_VECTOR))
+#define INTERCEPT_SS_GP_DF (INTERCEPT_SS_DF | BIT_ULL(GP_VECTOR))
+
+static void l2_ss_pending_test(void)
+{
+ GUEST_SYNC(SS_VECTOR);
+}
+
+static void l2_ss_injected_gp_test(void)
+{
+ GUEST_SYNC(GP_VECTOR);
+}
+
+static void l2_ss_injected_df_test(void)
+{
+ GUEST_SYNC(DF_VECTOR);
+}
+
+static void l2_ss_injected_tf_test(void)
+{
+ GUEST_SYNC(FAKE_TRIPLE_FAULT_VECTOR);
+}
+
+static void svm_run_l2(struct svm_test_data *svm, void *l2_code, int vector,
+ uint32_t error_code)
+{
+ struct vmcb *vmcb = svm->vmcb;
+ struct vmcb_control_area *ctrl = &vmcb->control;
+
+ vmcb->save.rip = (u64)l2_code;
+ run_guest(vmcb, svm->vmcb_gpa);
+
+ if (vector == FAKE_TRIPLE_FAULT_VECTOR)
+ return;
+
+ GUEST_ASSERT_EQ(ctrl->exit_code, (SVM_EXIT_EXCP_BASE + vector));
+ GUEST_ASSERT_EQ(ctrl->exit_info_1, error_code);
+}
+
+static void l1_svm_code(struct svm_test_data *svm)
+{
+ struct vmcb_control_area *ctrl = &svm->vmcb->control;
+ unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+
+ generic_svm_setup(svm, NULL, &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+ svm->vmcb->save.idtr.limit = 0;
+ ctrl->intercept |= BIT_ULL(INTERCEPT_SHUTDOWN);
+
+ ctrl->intercept_exceptions = INTERCEPT_SS_GP_DF;
+ svm_run_l2(svm, l2_ss_pending_test, SS_VECTOR, SS_ERROR_CODE);
+ svm_run_l2(svm, l2_ss_injected_gp_test, GP_VECTOR, GP_ERROR_CODE_AMD);
+
+ ctrl->intercept_exceptions = INTERCEPT_SS_DF;
+ svm_run_l2(svm, l2_ss_injected_df_test, DF_VECTOR, DF_ERROR_CODE);
+
+ ctrl->intercept_exceptions = INTERCEPT_SS;
+ svm_run_l2(svm, l2_ss_injected_tf_test, FAKE_TRIPLE_FAULT_VECTOR, 0);
+ GUEST_ASSERT_EQ(ctrl->exit_code, SVM_EXIT_SHUTDOWN);
+
+ GUEST_DONE();
+}
+
+static void vmx_run_l2(void *l2_code, int vector, uint32_t error_code)
+{
+ GUEST_ASSERT(!vmwrite(GUEST_RIP, (u64)l2_code));
+
+ GUEST_ASSERT_EQ(vector == SS_VECTOR ? vmlaunch() : vmresume(), 0);
+
+ if (vector == FAKE_TRIPLE_FAULT_VECTOR)
+ return;
+
+ GUEST_ASSERT_EQ(vmreadz(VM_EXIT_REASON), EXIT_REASON_EXCEPTION_NMI);
+ GUEST_ASSERT_EQ((vmreadz(VM_EXIT_INTR_INFO) & 0xff), vector);
+ GUEST_ASSERT_EQ(vmreadz(VM_EXIT_INTR_ERROR_CODE), error_code);
+}
+
+static void l1_vmx_code(struct vmx_pages *vmx)
+{
+ unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+
+ GUEST_ASSERT_EQ(prepare_for_vmx_operation(vmx), true);
+
+ GUEST_ASSERT_EQ(load_vmcs(vmx), true);
+
+ prepare_vmcs(vmx, NULL, &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+ GUEST_ASSERT_EQ(vmwrite(GUEST_IDTR_LIMIT, 0), 0);
+
+ /*
+ * VMX disallows injecting an exception with error_code[31:16] != 0,
+ * and hardware will never generate a VM-Exit with bits 31:16 set.
+ * KVM should likewise truncate the "bad" userspace value.
+ */
+ GUEST_ASSERT_EQ(vmwrite(EXCEPTION_BITMAP, INTERCEPT_SS_GP_DF), 0);
+ vmx_run_l2(l2_ss_pending_test, SS_VECTOR, (u16)SS_ERROR_CODE);
+ vmx_run_l2(l2_ss_injected_gp_test, GP_VECTOR, GP_ERROR_CODE_INTEL);
+
+ GUEST_ASSERT_EQ(vmwrite(EXCEPTION_BITMAP, INTERCEPT_SS_DF), 0);
+ vmx_run_l2(l2_ss_injected_df_test, DF_VECTOR, DF_ERROR_CODE);
+
+ GUEST_ASSERT_EQ(vmwrite(EXCEPTION_BITMAP, INTERCEPT_SS), 0);
+ vmx_run_l2(l2_ss_injected_tf_test, FAKE_TRIPLE_FAULT_VECTOR, 0);
+ GUEST_ASSERT_EQ(vmreadz(VM_EXIT_REASON), EXIT_REASON_TRIPLE_FAULT);
+
+ GUEST_DONE();
+}
+
+static void __attribute__((__flatten__)) l1_guest_code(void *test_data)
+{
+ if (cpu_has_svm())
+ l1_svm_code(test_data);
+ else
+ l1_vmx_code(test_data);
+}
+
+static void assert_ucall_vector(struct kvm_vm *vm, int vector)
+{
+ struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+ struct ucall uc;
+
+ TEST_ASSERT(run->exit_reason == KVM_EXIT_IO,
+ "Unexpected exit reason: %u (%s),\n",
+ run->exit_reason, exit_reason_str(run->exit_reason));
+
+ switch (get_ucall(vm, VCPU_ID, &uc)) {
+ case UCALL_SYNC:
+ TEST_ASSERT(vector == uc.args[1],
+ "Expected L2 to ask for %d, got %ld", vector, uc.args[1]);
+ break;
+ case UCALL_DONE:
+ TEST_ASSERT(vector == -1,
+ "Expected L2 to ask for %d, L2 says it's done", vector);
+ break;
+ case UCALL_ABORT:
+ TEST_FAIL("%s at %s:%ld (0x%lx != 0x%lx)",
+ (const char *)uc.args[0], __FILE__, uc.args[1],
+ uc.args[2], uc.args[3]);
+ break;
+ default:
+ TEST_FAIL("Expected L2 to ask for %d, got unexpected ucall %lu", vector, uc.cmd);
+ }
+}
+
+static void queue_ss_exception(struct kvm_vm *vm, bool inject)
+{
+ struct kvm_vcpu_events events;
+
+ vcpu_events_get(vm, VCPU_ID, &events);
+
+ TEST_ASSERT(!events.exception.pending,
+ "Vector %d unexpectedlt pending", events.exception.nr);
+ TEST_ASSERT(!events.exception.injected,
+ "Vector %d unexpectedly injected", events.exception.nr);
+
+ events.flags = KVM_VCPUEVENT_VALID_PAYLOAD;
+ events.exception.pending = !inject;
+ events.exception.injected = inject;
+ events.exception.nr = SS_VECTOR;
+ events.exception.has_error_code = true;
+ events.exception.error_code = SS_ERROR_CODE;
+ vcpu_events_set(vm, VCPU_ID, &events);
+}
+
+/*
+ * Verify KVM_{G,S}ET_EVENTS play nice with pending vs. injected exceptions
+ * when an exception is being queued for L2. Specifically, verify that KVM
+ * honors L1 exception intercept controls when a #SS is pending/injected,
+ * triggers a #GP on vectoring the #SS, morphs to #DF if #GP isn't intercepted
+ * by L1, and finally causes (nested) SHUTDOWN if #DF isn't intercepted by L1.
+ */
+int main(int argc, char *argv[])
+{
+ struct kvm_enable_cap cap_exception_payload = {
+ .cap = KVM_CAP_EXCEPTION_PAYLOAD,
+ .args[0] = -2ul,
+ };
+ vm_vaddr_t nested_test_data_gva;
+ struct kvm_vcpu_events events;
+ struct kvm_run *run;
+ struct kvm_vm *vm;
+
+ if (!kvm_check_cap(KVM_CAP_EXCEPTION_PAYLOAD)) {
+ pr_info("KVM_CAP_EXCEPTION_PAYLOAD not supported, skipping\n");
+ exit(KSFT_SKIP);
+ }
+
+ vm = vm_create_default(VCPU_ID, 0, l1_guest_code);
+ vm_enable_cap(vm, &cap_exception_payload);
+
+ if (nested_svm_supported()) {
+ vcpu_alloc_svm(vm, &nested_test_data_gva);
+ } else if (nested_vmx_supported()) {
+ vcpu_alloc_vmx(vm, &nested_test_data_gva);
+ } else {
+ pr_info("Nested virtualization not supported, skipping\n");
+ exit(KSFT_SKIP);
+ }
+
+ vcpu_args_set(vm, VCPU_ID, 1, nested_test_data_gva);
+ run = vcpu_state(vm, VCPU_ID);
+
+ /* Run L1 => L2. L2 should sync and request #SS. */
+ vcpu_run(vm, VCPU_ID);
+ assert_ucall_vector(vm, SS_VECTOR);
+
+ /* Pend #SS and request immediate exit. #SS should still be pending. */
+ queue_ss_exception(vm, false);
+ run->immediate_exit = true;
+ vcpu_run_complete_io(vm, VCPU_ID);
+
+ /* Verify the pending events comes back out the same as it went in. */
+ vcpu_events_get(vm, VCPU_ID, &events);
+ ASSERT_EQ(events.flags & KVM_VCPUEVENT_VALID_PAYLOAD,
+ KVM_VCPUEVENT_VALID_PAYLOAD);
+ ASSERT_EQ(events.exception.pending, true);
+ ASSERT_EQ(events.exception.nr, SS_VECTOR);
+ ASSERT_EQ(events.exception.has_error_code, true);
+ ASSERT_EQ(events.exception.error_code, SS_ERROR_CODE);
+
+ /*
+ * Run for real with the pending #SS, L1 should get a VM-Exit due to
+ * #SS interception and re-enter L2 to request #GP (via injected #SS).
+ */
+ run->immediate_exit = false;
+ vcpu_run(vm, VCPU_ID);
+ assert_ucall_vector(vm, GP_VECTOR);
+
+ /*
+ * Inject #SS, the #SS should bypass interception and cause #GP, which
+ * L1 should intercept before KVM morphs it to #DF. L1 should then
+ * disable #GP interception and run L2 to request #DF (via #SS => #GP).
+ */
+ queue_ss_exception(vm, true);
+ vcpu_run(vm, VCPU_ID);
+ assert_ucall_vector(vm, DF_VECTOR);
+
+ /*
+ * Inject #SS, the #SS should bypass interception and cause #GP, which
+ * L1 is no longer interception, and so should see a #DF VM-Exit. L1
+ * should then signal that is done.
+ */
+ queue_ss_exception(vm, true);
+ vcpu_run(vm, VCPU_ID);
+ assert_ucall_vector(vm, FAKE_TRIPLE_FAULT_VECTOR);
+
+ /*
+ * Inject #SS yet again. L1 is not intercepting #GP or #DF, and so
+ * should see nested TRIPLE_FAULT / SHUTDOWN.
+ */
+ queue_ss_exception(vm, true);
+ vcpu_run(vm, VCPU_ID);
+ assert_ucall_vector(vm, -1);
+
+ kvm_vm_free(vm);
+}
--
2.35.1.723.g4982287a31-goog