KVM: selftests: Add test for SMCCC filter

Add a selftest for the SMCCC filter, ensuring basic UAPI constraints
(e.g. reserved ranges, non-overlapping ranges) are upheld. Additionally,
test that the DENIED and FWD_TO_USER work as intended.
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230404154050.2270077-14-oliver.upton@linux.dev

tools/testing/selftests/kvm/Makefile

@@ -141,6 +141,7 @@ TEST_GEN_PROGS_aarch64 += aarch64/get-reg-list
 TEST_GEN_PROGS_aarch64 += aarch64/hypercalls
 TEST_GEN_PROGS_aarch64 += aarch64/page_fault_test
 TEST_GEN_PROGS_aarch64 += aarch64/psci_test
+TEST_GEN_PROGS_aarch64 += aarch64/smccc_filter
 TEST_GEN_PROGS_aarch64 += aarch64/vcpu_width_config
 TEST_GEN_PROGS_aarch64 += aarch64/vgic_init
 TEST_GEN_PROGS_aarch64 += aarch64/vgic_irq

tools/testing/selftests/kvm/aarch64/smccc_filter.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * smccc_filter - Tests for the SMCCC filter UAPI.
+ *
+ * Copyright (c) 2023 Google LLC
+ *
+ * This test includes:
+ *  - Tests that the UAPI constraints are upheld by KVM. For example, userspace
+ *    is prevented from filtering the architecture range of SMCCC calls.
+ *  - Test that the filter actions (DENIED, FWD_TO_USER) work as intended.
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/psci.h>
+#include <stdint.h>
+
+#include "processor.h"
+#include "test_util.h"
+
+enum smccc_conduit {
+	HVC_INSN,
+	SMC_INSN,
+};
+
+#define for_each_conduit(conduit)					\
+	for (conduit = HVC_INSN; conduit <= SMC_INSN; conduit++)
+
+static void guest_main(uint32_t func_id, enum smccc_conduit conduit)
+{
+	struct arm_smccc_res res;
+
+	if (conduit == SMC_INSN)
+		smccc_smc(func_id, 0, 0, 0, 0, 0, 0, 0, &res);
+	else
+		smccc_hvc(func_id, 0, 0, 0, 0, 0, 0, 0, &res);
+
+	GUEST_SYNC(res.a0);
+}
+
+static int __set_smccc_filter(struct kvm_vm *vm, uint32_t start, uint32_t nr_functions,
+			      enum kvm_smccc_filter_action action)
+{
+	struct kvm_smccc_filter filter = {
+		.base		= start,
+		.nr_functions	= nr_functions,
+		.action		= action,
+	};
+
+	return __kvm_device_attr_set(vm->fd, KVM_ARM_VM_SMCCC_CTRL,
+				     KVM_ARM_VM_SMCCC_FILTER, &filter);
+}
+
+static void set_smccc_filter(struct kvm_vm *vm, uint32_t start, uint32_t nr_functions,
+			     enum kvm_smccc_filter_action action)
+{
+	int ret = __set_smccc_filter(vm, start, nr_functions, action);
+
+	TEST_ASSERT(!ret, "failed to configure SMCCC filter: %d", ret);
+}
+
+static struct kvm_vm *setup_vm(struct kvm_vcpu **vcpu)
+{
+	struct kvm_vcpu_init init;
+	struct kvm_vm *vm;
+
+	vm = vm_create(1);
+	vm_ioctl(vm, KVM_ARM_PREFERRED_TARGET, &init);
+
+	/*
+	 * Enable in-kernel emulation of PSCI to ensure that calls are denied
+	 * due to the SMCCC filter, not because of KVM.
+	 */
+	init.features[0] |= (1 << KVM_ARM_VCPU_PSCI_0_2);
+
+	*vcpu = aarch64_vcpu_add(vm, 0, &init, guest_main);
+	return vm;
+}
+
+static void test_pad_must_be_zero(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm = setup_vm(&vcpu);
+	struct kvm_smccc_filter filter = {
+		.base		= PSCI_0_2_FN_PSCI_VERSION,
+		.nr_functions	= 1,
+		.action		= KVM_SMCCC_FILTER_DENY,
+		.pad		= { -1 },
+	};
+	int r;
+
+	r = __kvm_device_attr_set(vm->fd, KVM_ARM_VM_SMCCC_CTRL,
+				  KVM_ARM_VM_SMCCC_FILTER, &filter);
+	TEST_ASSERT(r < 0 && errno == EINVAL,
+		    "Setting filter with nonzero padding should return EINVAL");
+}
+
+/* Ensure that userspace cannot filter the Arm Architecture SMCCC range */
+static void test_filter_reserved_range(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm = setup_vm(&vcpu);
+	int r;
+
+	r = __set_smccc_filter(vm, ARM_SMCCC_ARCH_WORKAROUND_1,
+			       1, KVM_SMCCC_FILTER_DENY);
+	TEST_ASSERT(r < 0 && errno == EEXIST,
+		    "Attempt to filter reserved range should return EEXIST");
+
+	kvm_vm_free(vm);
+}
+
+static void test_invalid_nr_functions(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm = setup_vm(&vcpu);
+	int r;
+
+	r = __set_smccc_filter(vm, PSCI_0_2_FN64_CPU_ON, 0, KVM_SMCCC_FILTER_DENY);
+	TEST_ASSERT(r < 0 && errno == EINVAL,
+		    "Attempt to filter 0 functions should return EINVAL");
+
+	kvm_vm_free(vm);
+}
+
+static void test_overflow_nr_functions(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm = setup_vm(&vcpu);
+	int r;
+
+	r = __set_smccc_filter(vm, ~0, ~0, KVM_SMCCC_FILTER_DENY);
+	TEST_ASSERT(r < 0 && errno == EINVAL,
+		    "Attempt to overflow filter range should return EINVAL");
+
+	kvm_vm_free(vm);
+}
+
+static void test_reserved_action(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm = setup_vm(&vcpu);
+	int r;
+
+	r = __set_smccc_filter(vm, PSCI_0_2_FN64_CPU_ON, 1, -1);
+	TEST_ASSERT(r < 0 && errno == EINVAL,
+		    "Attempt to use reserved filter action should return EINVAL");
+
+	kvm_vm_free(vm);
+}
+
+
+/* Test that overlapping configurations of the SMCCC filter are rejected */
+static void test_filter_overlap(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm = setup_vm(&vcpu);
+	int r;
+
+	set_smccc_filter(vm, PSCI_0_2_FN64_CPU_ON, 1, KVM_SMCCC_FILTER_DENY);
+
+	r = __set_smccc_filter(vm, PSCI_0_2_FN64_CPU_ON, 1, KVM_SMCCC_FILTER_DENY);
+	TEST_ASSERT(r < 0 && errno == EEXIST,
+		    "Attempt to filter already configured range should return EEXIST");
+
+	kvm_vm_free(vm);
+}
+
+static void expect_call_denied(struct kvm_vcpu *vcpu)
+{
+	struct ucall uc;
+
+	if (get_ucall(vcpu, &uc) != UCALL_SYNC)
+		TEST_FAIL("Unexpected ucall: %lu\n", uc.cmd);
+
+	TEST_ASSERT(uc.args[1] == SMCCC_RET_NOT_SUPPORTED,
+		    "Unexpected SMCCC return code: %lu", uc.args[1]);
+}
+
+/* Denied SMCCC calls have a return code of SMCCC_RET_NOT_SUPPORTED */
+static void test_filter_denied(void)
+{
+	enum smccc_conduit conduit;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+
+	for_each_conduit(conduit) {
+		vm = setup_vm(&vcpu);
+
+		set_smccc_filter(vm, PSCI_0_2_FN_PSCI_VERSION, 1, KVM_SMCCC_FILTER_DENY);
+		vcpu_args_set(vcpu, 2, PSCI_0_2_FN_PSCI_VERSION, conduit);
+
+		vcpu_run(vcpu);
+		expect_call_denied(vcpu);
+
+		kvm_vm_free(vm);
+	}
+}
+
+static void expect_call_fwd_to_user(struct kvm_vcpu *vcpu, uint32_t func_id,
+				    enum smccc_conduit conduit)
+{
+	struct kvm_run *run = vcpu->run;
+
+	TEST_ASSERT(run->exit_reason == KVM_EXIT_HYPERCALL,
+		    "Unexpected exit reason: %u", run->exit_reason);
+	TEST_ASSERT(run->hypercall.nr == func_id,
+		    "Unexpected SMCCC function: %llu", run->hypercall.nr);
+
+	if (conduit == SMC_INSN)
+		TEST_ASSERT(run->hypercall.flags & KVM_HYPERCALL_EXIT_SMC,
+			    "KVM_HYPERCALL_EXIT_SMC is not set");
+	else
+		TEST_ASSERT(!(run->hypercall.flags & KVM_HYPERCALL_EXIT_SMC),
+			    "KVM_HYPERCAL_EXIT_SMC is set");
+}
+
+/* SMCCC calls forwarded to userspace cause KVM_EXIT_HYPERCALL exits */
+static void test_filter_fwd_to_user(void)
+{
+	enum smccc_conduit conduit;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+
+	for_each_conduit(conduit) {
+		vm = setup_vm(&vcpu);
+
+		set_smccc_filter(vm, PSCI_0_2_FN_PSCI_VERSION, 1, KVM_SMCCC_FILTER_FWD_TO_USER);
+		vcpu_args_set(vcpu, 2, PSCI_0_2_FN_PSCI_VERSION, conduit);
+
+		vcpu_run(vcpu);
+		expect_call_fwd_to_user(vcpu, PSCI_0_2_FN_PSCI_VERSION, conduit);
+
+		kvm_vm_free(vm);
+	}
+}
+
+static bool kvm_supports_smccc_filter(void)
+{
+	struct kvm_vm *vm = vm_create_barebones();
+	int r;
+
+	r = __kvm_has_device_attr(vm->fd, KVM_ARM_VM_SMCCC_CTRL, KVM_ARM_VM_SMCCC_FILTER);
+
+	kvm_vm_free(vm);
+	return !r;
+}
+
+int main(void)
+{
+	TEST_REQUIRE(kvm_supports_smccc_filter());
+
+	test_pad_must_be_zero();
+	test_invalid_nr_functions();
+	test_overflow_nr_functions();
+	test_reserved_action();
+	test_filter_reserved_range();
+	test_filter_overlap();
+	test_filter_denied();
+	test_filter_fwd_to_user();
+}