KVM: selftests: guest_memfd mmap() test when mmap is supported

Expand the guest_memfd selftests to comprehensively test host userspace
mmap functionality for guest_memfd-backed memory when supported by the
VM type.

Introduce new test cases to verify the following:

* Successful mmap operations: Ensure that MAP_SHARED mappings succeed
  when guest_memfd mmap is enabled.

* Data integrity: Validate that data written to the mmap'd region is
  correctly persistent and readable.

* fallocate interaction: Test that fallocate(FALLOC_FL_PUNCH_HOLE)
  correctly zeros out mapped pages.

* Out-of-bounds access: Verify that accessing memory beyond the
  guest_memfd's size correctly triggers a SIGBUS signal.

* Unsupported mmap: Confirm that mmap attempts fail as expected when
  guest_memfd mmap support is not enabled for the specific guest_memfd
  instance or VM type.

* Flag validity: Introduce test_vm_type_gmem_flag_validity() to
  systematically test that only allowed guest_memfd creation flags are
  accepted for different VM types (e.g., GUEST_MEMFD_FLAG_MMAP for
  default VMs, no flags for CoCo VMs).

The existing tests for guest_memfd creation (multiple instances, invalid
sizes), file read/write, file size, and invalid punch hole operations
are integrated into the new test_with_type() framework to allow testing
across different VM types.

Cc: James Houghton <[email protected]>
Cc: Gavin Shan <[email protected]>
Cc: Shivank Garg <[email protected]>
Co-developed-by: Ackerley Tng <[email protected]>
Signed-off-by: Ackerley Tng <[email protected]>
Signed-off-by: Fuad Tabba <[email protected]>
Co-developed-by: Sean Christopherson <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Message-ID: <[email protected]>
[Fix default vm_types to use BIT() - Paolo]
Signed-off-by: Paolo Bonzini <[email protected]>

Author: Fuad Tabba

tools/testing/selftests/kvm/guest_memfd_test.c

@@ -13,6 +13,8 @@
 
 #include <linux/bitmap.h>
 #include <linux/falloc.h>
+#include <setjmp.h>
+#include <signal.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -34,12 +36,83 @@ static void test_file_read_write(int fd)
 		    "pwrite on a guest_mem fd should fail");
 }
 
-static void test_mmap(int fd, size_t page_size)
+static void test_mmap_supported(int fd, size_t page_size, size_t total_size)
+{
+	const char val = 0xaa;
+	char *mem;
+	size_t i;
+	int ret;
+
+	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	TEST_ASSERT(mem == MAP_FAILED, "Copy-on-write not allowed by guest_memfd.");
+
+	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() for guest_memfd should succeed.");
+
+	memset(mem, val, total_size);
+	for (i = 0; i < total_size; i++)
+		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
+
+	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0,
+			page_size);
+	TEST_ASSERT(!ret, "fallocate the first page should succeed.");
+
+	for (i = 0; i < page_size; i++)
+		TEST_ASSERT_EQ(READ_ONCE(mem[i]), 0x00);
+	for (; i < total_size; i++)
+		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
+
+	memset(mem, val, page_size);
+	for (i = 0; i < total_size; i++)
+		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
+
+	ret = munmap(mem, total_size);
+	TEST_ASSERT(!ret, "munmap() should succeed.");
+}
+
+static sigjmp_buf jmpbuf;
+void fault_sigbus_handler(int signum)
+{
+	siglongjmp(jmpbuf, 1);
+}
+
+static void test_fault_overflow(int fd, size_t page_size, size_t total_size)
+{
+	struct sigaction sa_old, sa_new = {
+		.sa_handler = fault_sigbus_handler,
+	};
+	size_t map_size = total_size * 4;
+	const char val = 0xaa;
+	char *mem;
+	size_t i;
+	int ret;
+
+	mem = mmap(NULL, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() for guest_memfd should succeed.");
+
+	sigaction(SIGBUS, &sa_new, &sa_old);
+	if (sigsetjmp(jmpbuf, 1) == 0) {
+		memset(mem, 0xaa, map_size);
+		TEST_ASSERT(false, "memset() should have triggered SIGBUS.");
+	}
+	sigaction(SIGBUS, &sa_old, NULL);
+
+	for (i = 0; i < total_size; i++)
+		TEST_ASSERT_EQ(READ_ONCE(mem[i]), val);
+
+	ret = munmap(mem, map_size);
+	TEST_ASSERT(!ret, "munmap() should succeed.");
+}
+
+static void test_mmap_not_supported(int fd, size_t page_size, size_t total_size)
 {
 	char *mem;
 
 	mem = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 	TEST_ASSERT_EQ(mem, MAP_FAILED);
+
+	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT_EQ(mem, MAP_FAILED);
 }
 
 static void test_file_size(int fd, size_t page_size, size_t total_size)
@@ -120,26 +193,19 @@ static void test_invalid_punch_hole(int fd, size_t page_size, size_t total_size)
 	}
 }
 
-static void test_create_guest_memfd_invalid(struct kvm_vm *vm)
+static void test_create_guest_memfd_invalid_sizes(struct kvm_vm *vm,
+						  uint64_t guest_memfd_flags,
+						  size_t page_size)
 {
-	size_t page_size = getpagesize();
-	uint64_t flag;
 	size_t size;
 	int fd;
 
 	for (size = 1; size < page_size; size++) {
-		fd = __vm_create_guest_memfd(vm, size, 0);
-		TEST_ASSERT(fd == -1 && errno == EINVAL,
+		fd = __vm_create_guest_memfd(vm, size, guest_memfd_flags);
+		TEST_ASSERT(fd < 0 && errno == EINVAL,
 			    "guest_memfd() with non-page-aligned page size '0x%lx' should fail with EINVAL",
 			    size);
 	}
-
-	for (flag = BIT(0); flag; flag <<= 1) {
-		fd = __vm_create_guest_memfd(vm, page_size, flag);
-		TEST_ASSERT(fd == -1 && errno == EINVAL,
-			    "guest_memfd() with flag '0x%lx' should fail with EINVAL",
-			    flag);
-	}
 }
 
 static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
@@ -171,30 +237,81 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
 	close(fd1);
 }
 
-int main(int argc, char *argv[])
+static void test_guest_memfd_flags(struct kvm_vm *vm, uint64_t valid_flags)
 {
-	size_t page_size;
-	size_t total_size;
+	size_t page_size = getpagesize();
+	uint64_t flag;
 	int fd;
-	struct kvm_vm *vm;
 
-	TEST_REQUIRE(kvm_has_cap(KVM_CAP_GUEST_MEMFD));
+	for (flag = BIT(0); flag; flag <<= 1) {
+		fd = __vm_create_guest_memfd(vm, page_size, flag);
+		if (flag & valid_flags) {
+			TEST_ASSERT(fd >= 0,
+				    "guest_memfd() with flag '0x%lx' should succeed",
+				    flag);
+			close(fd);
+		} else {
+			TEST_ASSERT(fd < 0 && errno == EINVAL,
+				    "guest_memfd() with flag '0x%lx' should fail with EINVAL",
+				    flag);
+		}
+	}
+}
+
+static void test_guest_memfd(unsigned long vm_type)
+{
+	uint64_t flags = 0;
+	struct kvm_vm *vm;
+	size_t total_size;
+	size_t page_size;
+	int fd;
 
 	page_size = getpagesize();
 	total_size = page_size * 4;
 
-	vm = vm_create_barebones();
+	vm = vm_create_barebones_type(vm_type);
+
+	if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
+		flags |= GUEST_MEMFD_FLAG_MMAP;
 
-	test_create_guest_memfd_invalid(vm);
 	test_create_guest_memfd_multiple(vm);
+	test_create_guest_memfd_invalid_sizes(vm, flags, page_size);
 
-	fd = vm_create_guest_memfd(vm, total_size, 0);
+	fd = vm_create_guest_memfd(vm, total_size, flags);
 
 	test_file_read_write(fd);
-	test_mmap(fd, page_size);
+
+	if (flags & GUEST_MEMFD_FLAG_MMAP) {
+		test_mmap_supported(fd, page_size, total_size);
+		test_fault_overflow(fd, page_size, total_size);
+	} else {
+		test_mmap_not_supported(fd, page_size, total_size);
+	}
+
 	test_file_size(fd, page_size, total_size);
 	test_fallocate(fd, page_size, total_size);
 	test_invalid_punch_hole(fd, page_size, total_size);
 
+	test_guest_memfd_flags(vm, flags);
+
 	close(fd);
+	kvm_vm_free(vm);
+}
+
+int main(int argc, char *argv[])
+{
+	unsigned long vm_types, vm_type;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_GUEST_MEMFD));
+
+	/*
+	 * Not all architectures support KVM_CAP_VM_TYPES. However, those that
+	 * support guest_memfd have that support for the default VM type.
+	 */
+	vm_types = kvm_check_cap(KVM_CAP_VM_TYPES);
+	if (!vm_types)
+		vm_types = BIT(VM_TYPE_DEFAULT);
+
+	for_each_set_bit(vm_type, &vm_types, BITS_PER_TYPE(vm_types))
+		test_guest_memfd(vm_type);
 }