[PATCH v2 13/13] KVM: selftests: Add test for SMCCC filter

Oliver Upton
2023-03-30T15:50:31Z

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>
---
tools/testing/selftests/kvm/Makefile | 1 +
.../selftests/kvm/aarch64/smccc_filter.c | 196 ++++++++++++++++++
2 files changed, 197 insertions(+)
create mode 100644 tools/testing/selftests/kvm/aarch64/smccc_filter.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 84a627c43795..d66a0642cffd 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/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
diff --git a/tools/testing/selftests/kvm/aarch64/smccc_filter.c b/tools/testing/selftests/kvm/aarch64/smccc_filter.c
new file mode 100644
index 000000000000..7f4950d18b42
--- /dev/null
+++ b/tools/testing/selftests/kvm/aarch64/smccc_filter.c
@@ -0,0 +1,196 @@
+// 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;
+}
+
+/* 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, "Attempt to filter reserved range unexpectedly succeeded");
+
+ 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, "Attempt to filter already configured range unexpectedly succeeded");
+
+ 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_filter_reserved_range();
+ test_filter_overlap();
+ test_filter_denied();
+ test_filter_fwd_to_user();
+}
--
2.40.0.348.gf938b09366-goog