selftests: KVM: Test KVM_X86_QUIRK_FIX_HYPERCALL_INSN

Add a test that asserts KVM rewrites guest hypercall instructions to
match the running architecture (VMCALL on VMX, VMMCALL on SVM).
Additionally, test that with the quirk disabled, KVM no longer rewrites
guest instructions and instead injects a #UD.
Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20220316005538.2282772-3-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/.gitignore

@@ -15,6 +15,7 @@
 /x86_64/debug_regs
 /x86_64/evmcs_test
 /x86_64/emulator_error_test
+/x86_64/fix_hypercall_test
 /x86_64/get_msr_index_features
 /x86_64/kvm_clock_test
 /x86_64/kvm_pv_test

tools/testing/selftests/kvm/Makefile

@@ -48,6 +48,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/cr4_cpuid_sync_test
 TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
 TEST_GEN_PROGS_x86_64 += x86_64/evmcs_test
 TEST_GEN_PROGS_x86_64 += x86_64/emulator_error_test
+TEST_GEN_PROGS_x86_64 += x86_64/fix_hypercall_test
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_clock
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_cpuid
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_features

tools/testing/selftests/kvm/x86_64/fix_hypercall_test.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020, Google LLC.
+ *
+ * Tests for KVM paravirtual feature disablement
+ */
+#include <asm/kvm_para.h>
+#include <linux/kvm_para.h>
+#include <linux/stringify.h>
+#include <stdint.h>
+
+#include "apic.h"
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+
+#define VCPU_ID 0
+
+static bool ud_expected;
+
+static void guest_ud_handler(struct ex_regs *regs)
+{
+	GUEST_ASSERT(ud_expected);
+	GUEST_DONE();
+}
+
+extern unsigned char svm_hypercall_insn;
+static uint64_t svm_do_sched_yield(uint8_t apic_id)
+{
+	uint64_t ret;
+
+	asm volatile("mov %1, %%rax\n\t"
+		     "mov %2, %%rbx\n\t"
+		     "svm_hypercall_insn:\n\t"
+		     "vmmcall\n\t"
+		     "mov %%rax, %0\n\t"
+		     : "=r"(ret)
+		     : "r"((uint64_t)KVM_HC_SCHED_YIELD), "r"((uint64_t)apic_id)
+		     : "rax", "rbx", "memory");
+
+	return ret;
+}
+
+extern unsigned char vmx_hypercall_insn;
+static uint64_t vmx_do_sched_yield(uint8_t apic_id)
+{
+	uint64_t ret;
+
+	asm volatile("mov %1, %%rax\n\t"
+		     "mov %2, %%rbx\n\t"
+		     "vmx_hypercall_insn:\n\t"
+		     "vmcall\n\t"
+		     "mov %%rax, %0\n\t"
+		     : "=r"(ret)
+		     : "r"((uint64_t)KVM_HC_SCHED_YIELD), "r"((uint64_t)apic_id)
+		     : "rax", "rbx", "memory");
+
+	return ret;
+}
+
+static void assert_hypercall_insn(unsigned char *exp_insn, unsigned char *obs_insn)
+{
+	uint32_t exp = 0, obs = 0;
+
+	memcpy(&exp, exp_insn, sizeof(exp));
+	memcpy(&obs, obs_insn, sizeof(obs));
+
+	GUEST_ASSERT_EQ(exp, obs);
+}
+
+static void guest_main(void)
+{
+	unsigned char *native_hypercall_insn, *hypercall_insn;
+	uint8_t apic_id;
+
+	apic_id = GET_APIC_ID_FIELD(xapic_read_reg(APIC_ID));
+
+	if (is_intel_cpu()) {
+		native_hypercall_insn = &vmx_hypercall_insn;
+		hypercall_insn = &svm_hypercall_insn;
+		svm_do_sched_yield(apic_id);
+	} else if (is_amd_cpu()) {
+		native_hypercall_insn = &svm_hypercall_insn;
+		hypercall_insn = &vmx_hypercall_insn;
+		vmx_do_sched_yield(apic_id);
+	} else {
+		GUEST_ASSERT(0);
+		/* unreachable */
+		return;
+	}
+
+	GUEST_ASSERT(!ud_expected);
+	assert_hypercall_insn(native_hypercall_insn, hypercall_insn);
+	GUEST_DONE();
+}
+
+static void setup_ud_vector(struct kvm_vm *vm)
+{
+	vm_init_descriptor_tables(vm);
+	vcpu_init_descriptor_tables(vm, VCPU_ID);
+	vm_install_exception_handler(vm, UD_VECTOR, guest_ud_handler);
+}
+
+static void enter_guest(struct kvm_vm *vm)
+{
+	struct kvm_run *run;
+	struct ucall uc;
+
+	run = vcpu_state(vm, VCPU_ID);
+
+	vcpu_run(vm, VCPU_ID);
+	switch (get_ucall(vm, VCPU_ID, &uc)) {
+	case UCALL_SYNC:
+		pr_info("%s: %016lx\n", (const char *)uc.args[2], uc.args[3]);
+		break;
+	case UCALL_DONE:
+		return;
+	case UCALL_ABORT:
+		TEST_FAIL("%s at %s:%ld", (const char *)uc.args[0], __FILE__, uc.args[1]);
+	default:
+		TEST_FAIL("Unhandled ucall: %ld\nexit_reason: %u (%s)",
+			  uc.cmd, run->exit_reason, exit_reason_str(run->exit_reason));
+	}
+}
+
+static void test_fix_hypercall(void)
+{
+	struct kvm_vm *vm;
+
+	vm = vm_create_default(VCPU_ID, 0, guest_main);
+	setup_ud_vector(vm);
+
+	ud_expected = false;
+	sync_global_to_guest(vm, ud_expected);
+
+	virt_pg_map(vm, APIC_DEFAULT_GPA, APIC_DEFAULT_GPA);
+
+	enter_guest(vm);
+}
+
+static void test_fix_hypercall_disabled(void)
+{
+	struct kvm_enable_cap cap = {0};
+	struct kvm_vm *vm;
+
+	vm = vm_create_default(VCPU_ID, 0, guest_main);
+	setup_ud_vector(vm);
+
+	cap.cap = KVM_CAP_DISABLE_QUIRKS2;
+	cap.args[0] = KVM_X86_QUIRK_FIX_HYPERCALL_INSN;
+	vm_enable_cap(vm, &cap);
+
+	ud_expected = true;
+	sync_global_to_guest(vm, ud_expected);
+
+	virt_pg_map(vm, APIC_DEFAULT_GPA, APIC_DEFAULT_GPA);
+
+	enter_guest(vm);
+}
+
+int main(void)
+{
+	if (!(kvm_check_cap(KVM_CAP_DISABLE_QUIRKS2) & KVM_X86_QUIRK_FIX_HYPERCALL_INSN)) {
+		print_skip("KVM_X86_QUIRK_HYPERCALL_INSN not supported");
+		exit(KSFT_SKIP);
+	}
+
+	test_fix_hypercall();
+	test_fix_hypercall_disabled();
+}