[PATCH v7 10/11] KVM: selftests: Test disabling NX hugepages on a VM

Ben Gardon
2022-05-03T18:31:33Z

Add an argument to the NX huge pages test to test disabling the feature
on a VM using the new capability.

Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
---
.../selftests/kvm/include/kvm_util_base.h | 2 +
tools/testing/selftests/kvm/lib/kvm_util.c | 27 ++++++-
.../selftests/kvm/x86_64/nx_huge_pages_test.c | 70 +++++++++++++++----
.../kvm/x86_64/nx_huge_pages_test.sh | 12 +++-
4 files changed, 95 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
index 1dac3c6607f1..eee96189c1c4 100644
--- a/tools/testing/selftests/kvm/include/kvm_util_base.h
+++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
@@ -414,4 +414,6 @@ uint64_t vm_get_stat(struct kvm_vm *vm, const char *stat_name);

uint32_t guest_get_vcpuid(void);

+int __vm_disable_nx_huge_pages(struct kvm_vm *vm);
+
#endif /* SELFTEST_KVM_UTIL_BASE_H */
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 27ffd2537df6..0ec7efc2900d 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -112,6 +112,11 @@ int vm_check_cap(struct kvm_vm *vm, long cap)
return ret;
}

+static int __vm_enable_cap(struct kvm_vm *vm, struct kvm_enable_cap *cap)
+{
+ return ioctl(vm->fd, KVM_ENABLE_CAP, cap);
+}
+
/* VM Enable Capability
*
* Input Args:
@@ -128,7 +133,7 @@ int vm_enable_cap(struct kvm_vm *vm, struct kvm_enable_cap *cap)
{
int ret;

- ret = ioctl(vm->fd, KVM_ENABLE_CAP, cap);
+ ret = __vm_enable_cap(vm, cap);
TEST_ASSERT(ret == 0, "KVM_ENABLE_CAP IOCTL failed,\n"
" rc: %i errno: %i", ret, errno);

@@ -2758,3 +2763,23 @@ uint64_t vm_get_stat(struct kvm_vm *vm, const char *stat_name)
stat_name, ret);
return data;
}
+
+/* VM disable NX huge pages
+ *
+ * Input Args:
+ * vm - Virtual Machine
+ *
+ * Output Args: None
+ *
+ * Return: On success, 0 -ERRNO on failure.
+ *
+ * Disables NX huge pages for the VM.
+ */
+int __vm_disable_nx_huge_pages(struct kvm_vm *vm)
+{
+ struct kvm_enable_cap cap = { 0 };
+
+ cap.cap = KVM_CAP_VM_DISABLE_NX_HUGE_PAGES;
+ cap.args[0] = 0;
+ return __vm_enable_cap(vm, &cap);
+}
diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
index 238a6047791c..1e7328dd33d2 100644
--- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
+++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c
@@ -13,6 +13,8 @@
#include <fcntl.h>
#include <stdint.h>
#include <time.h>
+#include <linux/reboot.h>
+#include <sys/syscall.h>

#include <test_util.h>
#include "kvm_util.h"
@@ -89,18 +91,36 @@ static void check_split_count(struct kvm_vm *vm, int expected_splits)
expected_splits, actual_splits);
}

-int main(int argc, char **argv)
+void run_test(bool disable_nx_huge_pages, bool reboot_permissions)
{
struct kvm_vm *vm;
struct timespec ts;
+ uint64_t pages;
void *hva;
-
- if (argc != 2 || strtol(argv[1], NULL, 0) != MAGIC_TOKEN) {
- printf("This test must be run through nx_huge_pages_test.sh");
- return KSFT_SKIP;
+ int r;
+
+ pages = vm_pages_needed(VM_MODE_DEFAULT, 1, DEFAULT_GUEST_PHY_PAGES,
+ 0, 0);
+ vm = vm_create_without_vcpus(VM_MODE_DEFAULT, pages);
+
+ if (disable_nx_huge_pages) {
+ /*
+ * Cannot run the test without NX huge pages if the kernel
+ * does not support it.
+ */
+ if (!kvm_check_cap(KVM_CAP_VM_DISABLE_NX_HUGE_PAGES))
+ return;
+
+ r = __vm_disable_nx_huge_pages(vm);
+ if (reboot_permissions) {
+ TEST_ASSERT(!r, "Disabling NX huge pages should succeed if process has reboot permissions");
+ } else {
+ TEST_ASSERT(r == -EPERM, "This process should not have permission to disable NX huge pages");
+ return;
+ }
}

- vm = vm_create_default(0, 0, guest_code);
+ vm_vcpu_add_default(vm, 0, guest_code);

vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB,
HPAGE_GPA, HPAGE_SLOT,
@@ -133,23 +153,27 @@ int main(int argc, char **argv)
/*
* Next, the guest will execute from the first huge page, causing it
* to be remapped at 4k.
+ *
+ * If NX huge pages are disabled, this should have no effect.
*/
vcpu_run(vm, 0);
- check_2m_page_count(vm, 1);
- check_split_count(vm, 1);
+ check_2m_page_count(vm, disable_nx_huge_pages ? 2 : 1);
+ check_split_count(vm, disable_nx_huge_pages ? 0 : 1);

/*
* Executing from the third huge page (previously unaccessed) will
* cause part to be mapped at 4k.
+ *
+ * If NX huge pages are disabled, it should be mapped at 2M.
*/
vcpu_run(vm, 0);
- check_2m_page_count(vm, 1);
- check_split_count(vm, 2);
+ check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 1);
+ check_split_count(vm, disable_nx_huge_pages ? 0 : 2);

/* Reading from the first huge page again should have no effect. */
vcpu_run(vm, 0);
- check_2m_page_count(vm, 1);
- check_split_count(vm, 2);
+ check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 1);
+ check_split_count(vm, disable_nx_huge_pages ? 0 : 2);

/*
* Give recovery thread time to run. The wrapper script sets
@@ -161,8 +185,11 @@ int main(int argc, char **argv)

/*
* Now that the reclaimer has run, all the split pages should be gone.
+ *
+ * If NX huge pages are disabled, the relaimer will not run, so
+ * nothing should change from here on.
*/
- check_2m_page_count(vm, 1);
+ check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 1);
check_split_count(vm, 0);

/*
@@ -170,10 +197,25 @@ int main(int argc, char **argv)
* reading from it causes a huge page mapping to be installed.
*/
vcpu_run(vm, 0);
- check_2m_page_count(vm, 2);
+ check_2m_page_count(vm, disable_nx_huge_pages ? 3 : 2);
check_split_count(vm, 0);

kvm_vm_free(vm);
+}
+
+int main(int argc, char **argv)
+{
+ bool reboot_permissions;
+
+ if (argc != 3 || strtol(argv[1], NULL, 0) != MAGIC_TOKEN) {
+ printf("This test must be run through nx_huge_pages_test.sh");
+ return KSFT_SKIP;
+ }
+
+ reboot_permissions = strtol(argv[2], NULL, 0);
+
+ run_test(false, reboot_permissions);
+ run_test(true, reboot_permissions);

return 0;
}
diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
index 60bfed8181b9..c21c1f639141 100755
--- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
+++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh
@@ -16,6 +16,8 @@ HUGE_PAGES=$(sudo cat /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages)

set +e

+NXECUTABLE="$(dirname $0)/nx_huge_pages_test"
+
(
set -e

@@ -24,7 +26,15 @@ set +e
sudo echo 100 > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms
sudo echo 3 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages

- "$(dirname $0)"/nx_huge_pages_test 887563923
+ # Test with reboot permissions
+ sudo setcap cap_sys_boot+ep $NXECUTABLE
+ $NXECUTABLE 887563923 1
+
+ # Test without reboot permissions
+ if [ $(whoami) != "root" ] ; then
+ sudo setcap cap_sys_boot-ep $NXECUTABLE
+ $NXECUTABLE 887563923 0
+ fi
)
RET=$?

--
2.36.0.464.gb9c8b46e94-goog