[RFC PATCH 35/39] KVM: selftests: Test that pinned pages block KVM from setting memory attributes to PRIVATE

[Ackerley Tng]

CONFIG_GUP_TEST provides userspace with an ioctl to invoke
pin_user_pages(), and this test uses the ioctl to pin pages, to check
that memory attributes cannot be set to private if shared pages are
pinned.

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile          |   1 +
 .../selftests/kvm/guest_memfd_pin_test.c      | 104 ++++++++++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/guest_memfd_pin_test.c

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 3c1f35456bfc..c5a1c8c7125a 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -136,6 +136,7 @@ TEST_GEN_PROGS_x86_64 += dirty_log_perf_test
 TEST_GEN_PROGS_x86_64 += guest_memfd_test
 TEST_GEN_PROGS_x86_64 += guest_memfd_hugetlb_reporting_test
 TEST_GEN_PROGS_x86_64 += guest_memfd_sharing_test
+TEST_GEN_PROGS_x86_64 += guest_memfd_pin_test
 TEST_GEN_PROGS_x86_64 += guest_print_test
 TEST_GEN_PROGS_x86_64 += hardware_disable_test
 TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus
diff --git a/tools/testing/selftests/kvm/guest_memfd_pin_test.c b/tools/testing/selftests/kvm/guest_memfd_pin_test.c
new file mode 100644
index 000000000000..b45fb8024970
--- /dev/null
+++ b/tools/testing/selftests/kvm/guest_memfd_pin_test.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Test that pinned pages block KVM from setting memory attributes to PRIVATE.
+ *
+ * Copyright (c) 2024, Google LLC.
+ */
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "../../../../mm/gup_test.h"
+
+#define GUEST_MEMFD_PIN_TEST_SLOT 10
+#define GUEST_MEMFD_PIN_TEST_GPA 0x50000000ULL
+#define GUEST_MEMFD_PIN_TEST_OFFSET 0
+
+static int gup_test_fd;
+
+void pin_pages(void *vaddr, uint64_t size)
+{
+	const struct pin_longterm_test args = {
+		.addr = (uint64_t)vaddr,
+		.size = size,
+		.flags = PIN_LONGTERM_TEST_FLAG_USE_WRITE,
+	};
+
+	TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_START, &args), 0);
+}
+
+void unpin_pages(void)
+{
+	TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_STOP), 0);
+}
+
+void run_test(void)
+{
+	struct kvm_vm *vm;
+	size_t page_size;
+	void *mem;
+	int fd;
+
+	vm = vm_create_barebones_type(KVM_X86_SW_PROTECTED_VM);
+
+	page_size = getpagesize();
+	fd = vm_create_guest_memfd(vm, page_size, 0);
+
+	mem = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd,
+		   GUEST_MEMFD_PIN_TEST_OFFSET);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap should return valid address");
+
+	/*
+	 * Setting up this memslot with a KVM_X86_SW_PROTECTED_VM marks all
+	 * offsets in the file as shared.
+	 */
+	vm_set_user_memory_region2(vm, GUEST_MEMFD_PIN_TEST_SLOT,
+				   KVM_MEM_GUEST_MEMFD,
+				   GUEST_MEMFD_PIN_TEST_GPA, page_size, mem, fd,
+				   GUEST_MEMFD_PIN_TEST_OFFSET);
+
+	/* Before pinning pages, toggling memory attributes should be fine. */
+	vm_mem_set_private(vm, GUEST_MEMFD_PIN_TEST_GPA, page_size);
+	vm_mem_set_shared(vm, GUEST_MEMFD_PIN_TEST_GPA, page_size);
+
+	pin_pages(mem, page_size);
+
+	/*
+	 * Pinning also faults pages in, so remove these pages from userspace
+	 * page tables to properly test that pinning blocks setting memory
+	 * attributes to private.
+	 */
+	TEST_ASSERT_EQ(madvise(mem, page_size, MADV_DONTNEED), 0);
+
+	/* Should fail since the page is still faulted in. */
+	TEST_ASSERT_EQ(__vm_set_memory_attributes(vm, GUEST_MEMFD_PIN_TEST_GPA,
+						  page_size,
+						  KVM_MEMORY_ATTRIBUTE_PRIVATE),
+		       -1);
+	TEST_ASSERT_EQ(errno, EINVAL);
+
+	unpin_pages();
+
+	/* With the pages unpinned, kvm can set this page to private. */
+	vm_mem_set_private(vm, GUEST_MEMFD_PIN_TEST_GPA, page_size);
+
+	kvm_vm_free(vm);
+	close(fd);
+}
+
+int main(int argc, char *argv[])
+{
+	gup_test_fd = open("/sys/kernel/debug/gup_test", O_RDWR);
+	/*
+	 * This test depends on CONFIG_GUP_TEST to provide a kernel module that
+	 * exposes pin_user_pages() to userspace.
+	 */
+	TEST_REQUIRE(gup_test_fd != -1);
+	TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM));
+
+	run_test();
+
+	return 0;
+}
-- 
2.46.0.598.g6f2099f65c-goog