KVM: selftests: Add test for user space MSR handling

Now that we have the ability to handle MSRs from user space and also to
select which ones we do want to prevent in-kernel KVM code from handling,
let's add a selftest to show case and verify the API.

Signed-off-by: Alexander Graf <graf@amazon.com>

Message-Id: <20200925143422.21718-9-graf@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: agraf

tools/testing/selftests/kvm/.gitignore

@@ -11,6 +11,7 @@
 /x86_64/set_sregs_test
 /x86_64/smm_test
 /x86_64/state_test
+/x86_64/user_msr_test
 /x86_64/vmx_preemption_timer_test
 /x86_64/svm_vmcall_test
 /x86_64/sync_regs_test

tools/testing/selftests/kvm/Makefile

@@ -55,6 +55,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/vmx_set_nested_state_test
 TEST_GEN_PROGS_x86_64 += x86_64/vmx_tsc_adjust_test
 TEST_GEN_PROGS_x86_64 += x86_64/xss_msr_test
 TEST_GEN_PROGS_x86_64 += x86_64/debug_regs
+TEST_GEN_PROGS_x86_64 += x86_64/user_msr_test
 TEST_GEN_PROGS_x86_64 += clear_dirty_log_test
 TEST_GEN_PROGS_x86_64 += demand_paging_test
 TEST_GEN_PROGS_x86_64 += dirty_log_test

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

@@ -0,0 +1,248 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * tests for KVM_CAP_X86_USER_SPACE_MSR and KVM_X86_SET_MSR_FILTER
+ *
+ * Copyright (C) 2020, Amazon Inc.
+ *
+ * This is a functional test to verify that we can deflect MSR events
+ * into user space.
+ */
+#define _GNU_SOURCE /* for program_invocation_short_name */
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+
+#include "kvm_util.h"
+#include "processor.h"
+
+#define VCPU_ID                  5
+
+static u32 msr_reads, msr_writes;
+
+static u8 bitmap_00000000[KVM_MSR_FILTER_MAX_BITMAP_SIZE];
+static u8 bitmap_00000000_write[KVM_MSR_FILTER_MAX_BITMAP_SIZE];
+static u8 bitmap_40000000[KVM_MSR_FILTER_MAX_BITMAP_SIZE];
+static u8 bitmap_c0000000[KVM_MSR_FILTER_MAX_BITMAP_SIZE];
+static u8 bitmap_c0000000_read[KVM_MSR_FILTER_MAX_BITMAP_SIZE];
+static u8 bitmap_deadbeef[1] = { 0x1 };
+
+static void deny_msr(uint8_t *bitmap, u32 msr)
+{
+	u32 idx = msr & (KVM_MSR_FILTER_MAX_BITMAP_SIZE - 1);
+
+	bitmap[idx / 8] &= ~(1 << (idx % 8));
+}
+
+static void prepare_bitmaps(void)
+{
+	memset(bitmap_00000000, 0xff, sizeof(bitmap_00000000));
+	memset(bitmap_00000000_write, 0xff, sizeof(bitmap_00000000_write));
+	memset(bitmap_40000000, 0xff, sizeof(bitmap_40000000));
+	memset(bitmap_c0000000, 0xff, sizeof(bitmap_c0000000));
+	memset(bitmap_c0000000_read, 0xff, sizeof(bitmap_c0000000_read));
+
+	deny_msr(bitmap_00000000_write, MSR_IA32_POWER_CTL);
+	deny_msr(bitmap_c0000000_read, MSR_SYSCALL_MASK);
+	deny_msr(bitmap_c0000000_read, MSR_GS_BASE);
+}
+
+struct kvm_msr_filter filter = {
+	.flags = KVM_MSR_FILTER_DEFAULT_DENY,
+	.ranges = {
+		{
+			.flags = KVM_MSR_FILTER_READ,
+			.base = 0x00000000,
+			.nmsrs = KVM_MSR_FILTER_MAX_BITMAP_SIZE * BITS_PER_BYTE,
+			.bitmap = bitmap_00000000,
+		}, {
+			.flags = KVM_MSR_FILTER_WRITE,
+			.base = 0x00000000,
+			.nmsrs = KVM_MSR_FILTER_MAX_BITMAP_SIZE * BITS_PER_BYTE,
+			.bitmap = bitmap_00000000_write,
+		}, {
+			.flags = KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE,
+			.base = 0x40000000,
+			.nmsrs = KVM_MSR_FILTER_MAX_BITMAP_SIZE * BITS_PER_BYTE,
+			.bitmap = bitmap_40000000,
+		}, {
+			.flags = KVM_MSR_FILTER_READ,
+			.base = 0xc0000000,
+			.nmsrs = KVM_MSR_FILTER_MAX_BITMAP_SIZE * BITS_PER_BYTE,
+			.bitmap = bitmap_c0000000_read,
+		}, {
+			.flags = KVM_MSR_FILTER_WRITE,
+			.base = 0xc0000000,
+			.nmsrs = KVM_MSR_FILTER_MAX_BITMAP_SIZE * BITS_PER_BYTE,
+			.bitmap = bitmap_c0000000,
+		}, {
+			.flags = KVM_MSR_FILTER_WRITE | KVM_MSR_FILTER_READ,
+			.base = 0xdeadbeef,
+			.nmsrs = 1,
+			.bitmap = bitmap_deadbeef,
+		},
+	},
+};
+
+struct kvm_msr_filter no_filter = {
+	.flags = KVM_MSR_FILTER_DEFAULT_ALLOW,
+};
+
+static void guest_msr_calls(bool trapped)
+{
+	/* This goes into the in-kernel emulation */
+	wrmsr(MSR_SYSCALL_MASK, 0);
+
+	if (trapped) {
+		/* This goes into user space emulation */
+		GUEST_ASSERT(rdmsr(MSR_SYSCALL_MASK) == MSR_SYSCALL_MASK);
+		GUEST_ASSERT(rdmsr(MSR_GS_BASE) == MSR_GS_BASE);
+	} else {
+		GUEST_ASSERT(rdmsr(MSR_SYSCALL_MASK) != MSR_SYSCALL_MASK);
+		GUEST_ASSERT(rdmsr(MSR_GS_BASE) != MSR_GS_BASE);
+	}
+
+	/* If trapped == true, this goes into user space emulation */
+	wrmsr(MSR_IA32_POWER_CTL, 0x1234);
+
+	/* This goes into the in-kernel emulation */
+	rdmsr(MSR_IA32_POWER_CTL);
+
+	/* Invalid MSR, should always be handled by user space exit */
+	GUEST_ASSERT(rdmsr(0xdeadbeef) == 0xdeadbeef);
+	wrmsr(0xdeadbeef, 0x1234);
+}
+
+static void guest_code(void)
+{
+	guest_msr_calls(true);
+
+	/*
+	 * Disable msr filtering, so that the kernel
+	 * handles everything in the next round
+	 */
+	GUEST_SYNC(0);
+
+	guest_msr_calls(false);
+
+	GUEST_DONE();
+}
+
+static int handle_ucall(struct kvm_vm *vm)
+{
+	struct ucall uc;
+
+	switch (get_ucall(vm, VCPU_ID, &uc)) {
+	case UCALL_ABORT:
+		TEST_FAIL("Guest assertion not met");
+		break;
+	case UCALL_SYNC:
+		vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &no_filter);
+		break;
+	case UCALL_DONE:
+		return 1;
+	default:
+		TEST_FAIL("Unknown ucall %lu", uc.cmd);
+	}
+
+	return 0;
+}
+
+static void handle_rdmsr(struct kvm_run *run)
+{
+	run->msr.data = run->msr.index;
+	msr_reads++;
+
+	if (run->msr.index == MSR_SYSCALL_MASK ||
+	    run->msr.index == MSR_GS_BASE) {
+		TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_FILTER,
+			    "MSR read trap w/o access fault");
+	}
+
+	if (run->msr.index == 0xdeadbeef) {
+		TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_UNKNOWN,
+			    "MSR deadbeef read trap w/o inval fault");
+	}
+}
+
+static void handle_wrmsr(struct kvm_run *run)
+{
+	/* ignore */
+	msr_writes++;
+
+	if (run->msr.index == MSR_IA32_POWER_CTL) {
+		TEST_ASSERT(run->msr.data == 0x1234,
+			    "MSR data for MSR_IA32_POWER_CTL incorrect");
+		TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_FILTER,
+			    "MSR_IA32_POWER_CTL trap w/o access fault");
+	}
+
+	if (run->msr.index == 0xdeadbeef) {
+		TEST_ASSERT(run->msr.data == 0x1234,
+			    "MSR data for deadbeef incorrect");
+		TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_UNKNOWN,
+			    "deadbeef trap w/o inval fault");
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_enable_cap cap = {
+		.cap = KVM_CAP_X86_USER_SPACE_MSR,
+		.args[0] = KVM_MSR_EXIT_REASON_INVAL |
+			   KVM_MSR_EXIT_REASON_UNKNOWN |
+			   KVM_MSR_EXIT_REASON_FILTER,
+	};
+	struct kvm_vm *vm;
+	struct kvm_run *run;
+	int rc;
+
+	/* Tell stdout not to buffer its content */
+	setbuf(stdout, NULL);
+
+	/* Create VM */
+	vm = vm_create_default(VCPU_ID, 0, guest_code);
+	vcpu_set_cpuid(vm, VCPU_ID, kvm_get_supported_cpuid());
+	run = vcpu_state(vm, VCPU_ID);
+
+	rc = kvm_check_cap(KVM_CAP_X86_USER_SPACE_MSR);
+	TEST_ASSERT(rc, "KVM_CAP_X86_USER_SPACE_MSR is available");
+	vm_enable_cap(vm, &cap);
+
+	rc = kvm_check_cap(KVM_CAP_X86_MSR_FILTER);
+	TEST_ASSERT(rc, "KVM_CAP_X86_MSR_FILTER is available");
+
+	prepare_bitmaps();
+	vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter);
+
+	while (1) {
+		rc = _vcpu_run(vm, VCPU_ID);
+
+		TEST_ASSERT(rc == 0, "vcpu_run failed: %d\n", rc);
+
+		switch (run->exit_reason) {
+		case KVM_EXIT_X86_RDMSR:
+			handle_rdmsr(run);
+			break;
+		case KVM_EXIT_X86_WRMSR:
+			handle_wrmsr(run);
+			break;
+		case KVM_EXIT_IO:
+			if (handle_ucall(vm))
+				goto done;
+			break;
+		}
+
+	}
+
+done:
+	TEST_ASSERT(msr_reads == 4, "Handled 4 rdmsr in user space");
+	TEST_ASSERT(msr_writes == 3, "Handled 3 wrmsr in user space");
+
+	kvm_vm_free(vm);
+
+	return 0;
+}