[PATCH 15/15] KVM: selftests: Add test for KVM_TRANSLATE2

Nikolas Wipper
2024-09-10T15:26:53Z

Add selftest for KVM_TRANSLATE2. There are four different subtests.

A basic translate test that checks whether access permissions are handled
correctly. A set bits test, that checks whether the accessed and dirty
bits are set correctly. An errors test, that checks negative cases of the
flags. And a fuzzy test on random guest page tables.

The tests currently use x86 specific paging code, so generalising them for
more platforms is hard. Once other architectures implement KVM_TRANSLATE2
they need to be split into arch specific and agnostic parts.

Signed-off-by: Nikolas Wipper <nikwip@amazon.de>
---
tools/testing/selftests/kvm/Makefile | 1 +
.../selftests/kvm/x86_64/kvm_translate2.c | 310 ++++++++++++++++++
2 files changed, 311 insertions(+)
create mode 100644 tools/testing/selftests/kvm/x86_64/kvm_translate2.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 45cb70c048bb..5bb2db679658 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -81,6 +81,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/hyperv_svm_test
TEST_GEN_PROGS_x86_64 += x86_64/hyperv_tlb_flush
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/kvm_translate2
TEST_GEN_PROGS_x86_64 += x86_64/monitor_mwait_test
TEST_GEN_PROGS_x86_64 += x86_64/nested_exceptions_test
TEST_GEN_PROGS_x86_64 += x86_64/platform_info_test
diff --git a/tools/testing/selftests/kvm/x86_64/kvm_translate2.c b/tools/testing/selftests/kvm/x86_64/kvm_translate2.c
new file mode 100644
index 000000000000..607af6376243
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/kvm_translate2.c
@@ -0,0 +1,310 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test for x86 KVM_TRANSLATE2
+ *
+ * Copyright © 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <linux/bitmap.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+
+#define CHECK_ACCESSED_BIT(pte, set, start) \
+ ({ \
+ for (int _i = start; _i <= PG_LEVEL_512G; _i++) { \
+ if (set) \
+ TEST_ASSERT( \
+ (*pte[_i] & PTE_ACCESSED_MASK) != 0, \
+ "Page not marked accessed on level %i", \
+ _i); \
+ else \
+ TEST_ASSERT( \
+ (*pte[_i] & PTE_ACCESSED_MASK) == 0, \
+ "Page marked accessed on level %i", \
+ _i); \
+ } \
+ })
+
+#define CHECK_DIRTY_BIT(pte, set) \
+ ({ \
+ if (set) \
+ TEST_ASSERT((*pte[PG_LEVEL_4K] & PTE_DIRTY_MASK) != 0, \
+ "Page not marked dirty"); \
+ else \
+ TEST_ASSERT((*pte[PG_LEVEL_4K] & PTE_DIRTY_MASK) == 0, \
+ "Page marked dirty"); \
+ })
+
+enum point_of_failure {
+ pof_none,
+ pof_ioctl,
+ pof_page_walk,
+ pof_no_failure,
+};
+
+struct kvm_translation2 kvm_translate2(struct kvm_vcpu *vcpu, uint64_t vaddr,
+ int flags, int access,
+ enum point_of_failure pof)
+{
+ struct kvm_translation2 tr = { .linear_address = vaddr,
+ .flags = flags,
+ .access = access };
+
+ int res = ioctl(vcpu->fd, KVM_TRANSLATE2, &tr);
+
+ if (pof == pof_none)
+ return tr;
+
+ if (pof == pof_ioctl) {
+ TEST_ASSERT(res == -1, "ioctl didn't fail");
+ return tr;
+ }
+
+ TEST_ASSERT(res != -1, "ioctl failed");
+ TEST_ASSERT((pof != pof_page_walk) == tr.valid,
+ "Page walk fail with code %u", tr.error_code);
+
+ return tr;
+}
+
+void test_translate(struct kvm_vm *vm, struct kvm_vcpu *vcpu, int index,
+ uint64_t *pte[PG_LEVEL_NUM], vm_vaddr_t vaddr)
+{
+ struct kvm_translation2 translation;
+ int access = index;
+
+ printf("%s - write: %u, user: %u, exec: %u ...\t",
+ __func__,
+ (access & KVM_TRANSLATE_ACCESS_WRITE) >> 0,
+ (access & KVM_TRANSLATE_ACCESS_USER) >> 1,
+ (access & KVM_TRANSLATE_ACCESS_EXEC) >> 2);
+
+ uint64_t mask = PTE_WRITABLE_MASK | PTE_USER_MASK | PTE_NX_MASK;
+ uint64_t new_value = 0;
+
+ if (access & KVM_TRANSLATE_ACCESS_WRITE)
+ new_value |= PTE_WRITABLE_MASK;
+ if (access & KVM_TRANSLATE_ACCESS_USER)
+ new_value |= PTE_USER_MASK;
+ if (!(access & KVM_TRANSLATE_ACCESS_EXEC))
+ new_value |= PTE_NX_MASK;
+
+ for (int i = PG_LEVEL_4K; i <= PG_LEVEL_512G; i++)
+ *pte[i] = (*pte[i] & ~mask) | new_value;
+
+ translation = kvm_translate2(vcpu, vaddr, 0, access, pof_no_failure);
+
+ TEST_ASSERT_EQ(*pte[PG_LEVEL_4K] & GENMASK(51, 12),
+ translation.physical_address);
+
+ /* Check configurations that have extra access requirements */
+ for (int i = 0; i < 8; i++) {
+ int case_access = i;
+
+ if ((case_access | access) <= access)
+ continue;
+
+ translation = kvm_translate2(vcpu, vaddr, 0, case_access,
+ pof_page_walk);
+ TEST_ASSERT_EQ(translation.error_code,
+ KVM_TRANSLATE_FAULT_PRIVILEGE_VIOLATION);
+ }
+
+ /* Clear accessed bits */
+ for (int i = PG_LEVEL_4K; i <= PG_LEVEL_512G; i++)
+ *pte[i] &= ~PTE_ACCESSED_MASK;
+
+ printf("[ok]\n");
+}
+
+void test_set_bits(struct kvm_vm *vm, struct kvm_vcpu *vcpu,
+ uint64_t *pte[PG_LEVEL_NUM], vm_vaddr_t vaddr)
+{
+ printf("%s ...\t", __func__);
+
+ /* Sanity checks */
+ CHECK_ACCESSED_BIT(pte, false, PG_LEVEL_4K);
+ CHECK_DIRTY_BIT(pte, false);
+
+ kvm_translate2(vcpu, vaddr, 0, 0, pof_no_failure);
+
+ CHECK_ACCESSED_BIT(pte, false, PG_LEVEL_4K);
+ CHECK_DIRTY_BIT(pte, false);
+
+ kvm_translate2(vcpu, vaddr, KVM_TRANSLATE_FLAGS_SET_ACCESSED, 0,
+ pof_no_failure);
+
+ CHECK_ACCESSED_BIT(pte, true, PG_LEVEL_4K);
+ CHECK_DIRTY_BIT(pte, false);
+
+ kvm_translate2(vcpu, vaddr,
+ KVM_TRANSLATE_FLAGS_SET_ACCESSED | KVM_TRANSLATE_FLAGS_SET_DIRTY,
+ KVM_TRANSLATE_ACCESS_WRITE, pof_no_failure);
+
+ CHECK_ACCESSED_BIT(pte, true, PG_LEVEL_4K);
+ CHECK_DIRTY_BIT(pte, true);
+
+ printf("[ok]\n");
+}
+
+void test_errors(struct kvm_vm *vm, struct kvm_vcpu *vcpu,
+ uint64_t *pte[PG_LEVEL_NUM], vm_vaddr_t vaddr)
+{
+ struct kvm_translation2 tr;
+
+ printf("%s ...\t", __func__);
+
+ /* Set an unsupported access bit */
+ kvm_translate2(vcpu, vaddr, 0, (1 << 3), pof_ioctl);
+ kvm_translate2(vcpu, vaddr, KVM_TRANSLATE_FLAGS_SET_DIRTY, 0, pof_ioctl);
+ kvm_translate2(vcpu, vaddr, KVM_TRANSLATE_FLAGS_FORCE_SET_ACCESSED, 0,
+ pof_ioctl);
+
+ /* Try to translate a non-canonical address */
+ tr = kvm_translate2(vcpu, 0b101ull << 60, 0, 0, pof_page_walk);
+ TEST_ASSERT_EQ(tr.error_code, KVM_TRANSLATE_FAULT_INVALID_GVA);
+
+ uint64_t old_pte = *pte[PG_LEVEL_2M];
+
+ *pte[PG_LEVEL_2M] |= (1ull << 51); /* Set a reserved bit */
+
+ tr = kvm_translate2(vcpu, vaddr, 0, 0, pof_page_walk);
+ TEST_ASSERT_EQ(tr.error_code, KVM_TRANSLATE_FAULT_RESERVED_BITS);
+
+ *pte[PG_LEVEL_2M] &= ~(1ull << 51);
+
+ /* Create a GPA that's definitely not mapped */
+ *pte[PG_LEVEL_2M] |= GENMASK(35, 13);
+
+ tr = kvm_translate2(vcpu, vaddr, 0, 0, pof_page_walk);
+ TEST_ASSERT_EQ(tr.error_code, KVM_TRANSLATE_FAULT_INVALID_GPA);
+
+ *pte[PG_LEVEL_2M] = old_pte;
+
+ /* Clear accessed bits */
+ for (int i = PG_LEVEL_4K; i <= PG_LEVEL_512G; i++)
+ *pte[i] &= ~PTE_ACCESSED_MASK;
+
+ /* Try translating a non-present page */
+ *pte[PG_LEVEL_4K] &= ~PTE_PRESENT_MASK;
+
+ tr = kvm_translate2(
+ vcpu, vaddr,
+ KVM_TRANSLATE_FLAGS_SET_ACCESSED |
+ KVM_TRANSLATE_FLAGS_FORCE_SET_ACCESSED, 0,
+ pof_page_walk);
+ TEST_ASSERT_EQ(tr.error_code, KVM_TRANSLATE_FAULT_NOT_PRESENT);
+ CHECK_ACCESSED_BIT(pte, true, PG_LEVEL_2M);
+
+ *pte[PG_LEVEL_4K] |= PTE_PRESENT_MASK;
+
+ /*
+ * Try setting accessed/dirty bits on a PTE that is in read-only memory
+ */
+ vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, 0x80000000, 1, 4,
+ KVM_MEM_READONLY);
+
+ uint64_t *addr = addr_gpa2hva(vm, 0x80000000);
+ uint64_t *base = addr_gpa2hva(vm, *pte[PG_LEVEL_2M] & GENMASK(51, 12));
+
+ /* Copy the entire page table */
+ for (int i = 0; i < 0x200; i += 1)
+ addr[i] = (base[i] & ~PTE_ACCESSED_MASK) | PTE_PRESENT_MASK;
+
+ uint64_t old_2m = *pte[PG_LEVEL_2M];
+ *pte[PG_LEVEL_2M] &= ~GENMASK(51, 12);
+ *pte[PG_LEVEL_2M] |= 0x80000000;
+
+ tr = kvm_translate2(vcpu, vaddr,
+ KVM_TRANSLATE_FLAGS_SET_ACCESSED |
+ KVM_TRANSLATE_FLAGS_SET_DIRTY |
+ KVM_TRANSLATE_FLAGS_FORCE_SET_ACCESSED,
+ KVM_TRANSLATE_ACCESS_WRITE, pof_no_failure);
+
+ TEST_ASSERT(!tr.set_bits_succeeded, "Page not read-only");
+
+ *pte[PG_LEVEL_2M] = old_2m;
+
+ printf("[ok]\n");
+}
+
+/* Test page walker stability, by trying to translate with garbage PTEs */
+void test_fuzz(struct kvm_vm *vm, struct kvm_vcpu *vcpu,
+ uint64_t *pte[PG_LEVEL_NUM], vm_vaddr_t vaddr)
+{
+ printf("%s ...\t", __func__);
+
+ /* Test gPTEs that point to random addresses */
+ for (int level = PG_LEVEL_4K; level < PG_LEVEL_NUM; level++) {
+ for (int i = 0; i < 10000; i++) {
+ uint64_t random_address = random() % GENMASK(29, 0) << 12;
+ *pte[level] = (*pte[level] & ~GENMASK(51, 12)) | random_address;
+
+ kvm_translate2(vcpu, vaddr,
+ KVM_TRANSLATE_FLAGS_SET_ACCESSED |
+ KVM_TRANSLATE_FLAGS_SET_DIRTY |
+ KVM_TRANSLATE_FLAGS_FORCE_SET_ACCESSED,
+ 0, pof_none);
+ }
+ }
+
+ /* Test gPTEs with completely random values */
+ for (int level = PG_LEVEL_4K; level < PG_LEVEL_NUM; level++) {
+ for (int i = 0; i < 10000; i++) {
+ *pte[level] = random();
+
+ kvm_translate2(vcpu, vaddr,
+ KVM_TRANSLATE_FLAGS_SET_ACCESSED |
+ KVM_TRANSLATE_FLAGS_SET_DIRTY |
+ KVM_TRANSLATE_FLAGS_FORCE_SET_ACCESSED,
+ 0, pof_none);
+ }
+ }
+
+ printf("[ok]\n");
+}
+
+int main(int argc, char *argv[])
+{
+ uint64_t *pte[PG_LEVEL_NUM];
+ struct kvm_vcpu *vcpu;
+ struct kvm_sregs regs;
+ struct kvm_vm *vm;
+ vm_vaddr_t vaddr;
+ int page_level;
+
+ TEST_REQUIRE(kvm_has_cap(KVM_CAP_TRANSLATE2));
+
+ vm = vm_create_with_one_vcpu(&vcpu, NULL);
+
+ vaddr = __vm_vaddr_alloc_page(vm, MEM_REGION_TEST_DATA);
+
+ for (page_level = PG_LEVEL_512G; page_level > PG_LEVEL_NONE;
+ page_level--) {
+ pte[page_level] = __vm_get_page_table_entry(vm, vaddr, &page_level);
+ }
+
+ /* Enable WP bit in cr0, so kernel accesses uphold write protection */
+ vcpu_ioctl(vcpu, KVM_GET_SREGS, &regs);
+ regs.cr0 |= 1 << 16;
+ vcpu_ioctl(vcpu, KVM_SET_SREGS, &regs);
+
+ for (int index = 0; index < 8; index++)
+ test_translate(vm, vcpu, index, pte, vaddr);
+
+ test_set_bits(vm, vcpu, pte, vaddr);
+ test_errors(vm, vcpu, pte, vaddr);
+ test_fuzz(vm, vcpu, pte, vaddr);
+
+ kvm_vm_free(vm);
+
+ return 0;
+}