selftests/bpf: Add tests for filesystem kfuncs

Add selftests for two new filesystem kfuncs:
  1. bpf_get_file_xattr
  2. bpf_get_fsverity_digest

These tests simply make sure the two kfuncs work. Another selftest will be
added to demonstrate how to use these kfuncs to verify file signature.

CONFIG_FS_VERITY is added to selftests config. However, this is not
sufficient to guarantee bpf_get_fsverity_digest works. This is because
fsverity need to be enabled at file system level (for example, with tune2fs
on ext4). If local file system doesn't have this feature enabled, just skip
the test.

Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231129234417.856536-6-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/bpf_kfuncs.h b/tools/testing/selftests/bpf/bpf_kfuncs.h
index 5ca68ff0b59fb13d38dfaa8b1e1d5f22e15c7add..c2c084a44eae487670b1f6393f5e774d66165da1 100644 (file)
--- a/tools/testing/selftests/bpf/bpf_kfuncs.h
+++ b/tools/testing/selftests/bpf/bpf_kfuncs.h
@@ -55,4 +55,7 @@ void *bpf_cast_to_kern_ctx(void *) __ksym;
 
 void *bpf_rdonly_cast(void *obj, __u32 btf_id) __ksym;
 
+extern int bpf_get_file_xattr(struct file *file, const char *name,
+                             struct bpf_dynptr *value_ptr) __ksym;
+extern int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr *digest_ptr) __ksym;
 #endif

diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
index 782876452acf964c48e839f07af593f3c1446d51..c125c441abc7c8d1fcc3094fb2999e9ca53c0183 100644 (file)
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config
@@ -23,6 +23,7 @@ CONFIG_FPROBE=y
 CONFIG_FTRACE_SYSCALLS=y
 CONFIG_FUNCTION_ERROR_INJECTION=y
 CONFIG_FUNCTION_TRACER=y
+CONFIG_FS_VERITY=y
 CONFIG_GENEVE=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y

diff --git a/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
new file mode 100644 (file)
index 0000000..d3196a4
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/fs_kfuncs.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/xattr.h>
+#include <linux/fsverity.h>
+#include <unistd.h>
+#include <test_progs.h>
+#include "test_get_xattr.skel.h"
+#include "test_fsverity.skel.h"
+
+static const char testfile[] = "/tmp/test_progs_fs_kfuncs";
+
+static void test_xattr(void)
+{
+       struct test_get_xattr *skel = NULL;
+       int fd = -1, err;
+
+       fd = open(testfile, O_CREAT | O_RDONLY, 0644);
+       if (!ASSERT_GE(fd, 0, "create_file"))
+               return;
+
+       close(fd);
+       fd = -1;
+
+       err = setxattr(testfile, "user.kfuncs", "hello", sizeof("hello"), 0);
+       if (!ASSERT_OK(err, "setxattr"))
+               goto out;
+
+       skel = test_get_xattr__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "test_get_xattr__open_and_load"))
+               goto out;
+
+       skel->bss->monitored_pid = getpid();
+       err = test_get_xattr__attach(skel);
+
+       if (!ASSERT_OK(err, "test_get_xattr__attach"))
+               goto out;
+
+       fd = open(testfile, O_RDONLY, 0644);
+       if (!ASSERT_GE(fd, 0, "open_file"))
+               goto out;
+
+       ASSERT_EQ(skel->bss->found_xattr, 1, "found_xattr");
+
+out:
+       close(fd);
+       test_get_xattr__destroy(skel);
+       remove(testfile);
+}
+
+#ifndef SHA256_DIGEST_SIZE
+#define SHA256_DIGEST_SIZE      32
+#endif
+
+static void test_fsverity(void)
+{
+       struct fsverity_enable_arg arg = {0};
+       struct test_fsverity *skel = NULL;
+       struct fsverity_digest *d;
+       int fd, err;
+       char buffer[4096];
+
+       fd = open(testfile, O_CREAT | O_RDWR, 0644);
+       if (!ASSERT_GE(fd, 0, "create_file"))
+               return;
+
+       /* Write random buffer, so the file is not empty */
+       err = write(fd, buffer, 4096);
+       if (!ASSERT_EQ(err, 4096, "write_file"))
+               goto out;
+       close(fd);
+
+       /* Reopen read-only, otherwise FS_IOC_ENABLE_VERITY will fail */
+       fd = open(testfile, O_RDONLY, 0644);
+       if (!ASSERT_GE(fd, 0, "open_file1"))
+               return;
+
+       /* Enable fsverity for the file.
+        * If the file system doesn't support verity, this will fail. Skip
+        * the test in such case.
+        */
+       arg.version = 1;
+       arg.hash_algorithm = FS_VERITY_HASH_ALG_SHA256;
+       arg.block_size = 4096;
+       err = ioctl(fd, FS_IOC_ENABLE_VERITY, &arg);
+       if (err) {
+               printf("%s:SKIP:local fs doesn't support fsverity (%d)\n"
+                      "To run this test, try enable CONFIG_FS_VERITY and enable FSVerity for the filesystem.\n",
+                      __func__, errno);
+               test__skip();
+               goto out;
+       }
+
+       skel = test_fsverity__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "test_fsverity__open_and_load"))
+               goto out;
+
+       /* Get fsverity_digest from ioctl */
+       d = (struct fsverity_digest *)skel->bss->expected_digest;
+       d->digest_algorithm = FS_VERITY_HASH_ALG_SHA256;
+       d->digest_size = SHA256_DIGEST_SIZE;
+       err = ioctl(fd, FS_IOC_MEASURE_VERITY, skel->bss->expected_digest);
+       if (!ASSERT_OK(err, "ioctl_FS_IOC_MEASURE_VERITY"))
+               goto out;
+
+       skel->bss->monitored_pid = getpid();
+       err = test_fsverity__attach(skel);
+       if (!ASSERT_OK(err, "test_fsverity__attach"))
+               goto out;
+
+       /* Reopen the file to trigger the program */
+       close(fd);
+       fd = open(testfile, O_RDONLY);
+       if (!ASSERT_GE(fd, 0, "open_file2"))
+               goto out;
+
+       ASSERT_EQ(skel->bss->got_fsverity, 1, "got_fsverity");
+       ASSERT_EQ(skel->bss->digest_matches, 1, "digest_matches");
+out:
+       close(fd);
+       test_fsverity__destroy(skel);
+       remove(testfile);
+}
+
+void test_fs_kfuncs(void)
+{
+       if (test__start_subtest("xattr"))
+               test_xattr();
+
+       if (test__start_subtest("fsverity"))
+               test_fsverity();
+}

diff --git a/tools/testing/selftests/bpf/progs/test_fsverity.c b/tools/testing/selftests/bpf/progs/test_fsverity.c
new file mode 100644 (file)
index 0000000..3975495
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_fsverity.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_kfuncs.h"
+
+char _license[] SEC("license") = "GPL";
+
+#ifndef SHA256_DIGEST_SIZE
+#define SHA256_DIGEST_SIZE      32
+#endif
+
+#define SIZEOF_STRUCT_FSVERITY_DIGEST 4  /* sizeof(struct fsverity_digest) */
+
+char expected_digest[SIZEOF_STRUCT_FSVERITY_DIGEST + SHA256_DIGEST_SIZE];
+char digest[SIZEOF_STRUCT_FSVERITY_DIGEST + SHA256_DIGEST_SIZE];
+__u32 monitored_pid;
+__u32 got_fsverity;
+__u32 digest_matches;
+
+SEC("lsm.s/file_open")
+int BPF_PROG(test_file_open, struct file *f)
+{
+       struct bpf_dynptr digest_ptr;
+       __u32 pid;
+       int ret;
+       int i;
+
+       pid = bpf_get_current_pid_tgid() >> 32;
+       if (pid != monitored_pid)
+               return 0;
+
+       bpf_dynptr_from_mem(digest, sizeof(digest), 0, &digest_ptr);
+       ret = bpf_get_fsverity_digest(f, &digest_ptr);
+       if (ret < 0)
+               return 0;
+       got_fsverity = 1;
+
+       for (i = 0; i < sizeof(digest); i++) {
+               if (digest[i] != expected_digest[i])
+                       return 0;
+       }
+
+       digest_matches = 1;
+       return 0;
+}

diff --git a/tools/testing/selftests/bpf/progs/test_get_xattr.c b/tools/testing/selftests/bpf/progs/test_get_xattr.c
new file mode 100644 (file)
index 0000000..7eb2a4e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_get_xattr.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_kfuncs.h"
+
+char _license[] SEC("license") = "GPL";
+
+__u32 monitored_pid;
+__u32 found_xattr;
+
+static const char expected_value[] = "hello";
+char value[32];
+
+SEC("lsm.s/file_open")
+int BPF_PROG(test_file_open, struct file *f)
+{
+       struct bpf_dynptr value_ptr;
+       __u32 pid;
+       int ret;
+
+       pid = bpf_get_current_pid_tgid() >> 32;
+       if (pid != monitored_pid)
+               return 0;
+
+       bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
+
+       ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
+       if (ret != sizeof(expected_value))
+               return 0;
+       if (bpf_strncmp(value, ret, expected_value))
+               return 0;
+       found_xattr = 1;
+       return 0;
+}