[PATCH bpf-next 3/5] bpf/selftests: Test using global cpumask kptr with RCU

David Vernet
2023-03-16T01:41:43Z

Now that struct bpf_cpumask * is considered an RCU-safe type according
to the verifier, we should add tests that validate its common usages.
This patch adds those tests to the cpumask test suite. A subsequent
changes will remove bpf_cpumask_kptr_get(), and will adjust the selftest
and BPF documentation accordingly.

Signed-off-by: David Vernet <void@manifault.com>
---
.../selftests/bpf/prog_tests/cpumask.c | 1 +
.../selftests/bpf/progs/cpumask_common.h | 6 ++
.../selftests/bpf/progs/cpumask_failure.c | 62 +++++++++++++++++++
.../selftests/bpf/progs/cpumask_success.c | 33 ++++++++++
4 files changed, 102 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/cpumask.c b/tools/testing/selftests/bpf/prog_tests/cpumask.c
index 5fbe457c4ebe..6c0fe23498c7 100644
--- a/tools/testing/selftests/bpf/prog_tests/cpumask.c
+++ b/tools/testing/selftests/bpf/prog_tests/cpumask.c
@@ -17,6 +17,7 @@ static const char * const cpumask_success_testcases[] = {
"test_insert_leave",
"test_insert_remove_release",
"test_insert_kptr_get_release",
+ "test_global_mask_rcu",
};

static void verify_success(const char *prog_name)
diff --git a/tools/testing/selftests/bpf/progs/cpumask_common.h b/tools/testing/selftests/bpf/progs/cpumask_common.h
index 65e5496ca1b2..7623782fbd62 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_common.h
+++ b/tools/testing/selftests/bpf/progs/cpumask_common.h
@@ -9,6 +9,9 @@

int err;

+#define private(name) SEC(".bss." #name) __hidden __attribute__((aligned(8)))
+private(MASK) static struct bpf_cpumask __kptr * global_mask;
+
struct __cpumask_map_value {
struct bpf_cpumask __kptr * cpumask;
};
@@ -51,6 +54,9 @@ void bpf_cpumask_copy(struct bpf_cpumask *dst, const struct cpumask *src) __ksym
u32 bpf_cpumask_any(const struct cpumask *src) __ksym;
u32 bpf_cpumask_any_and(const struct cpumask *src1, const struct cpumask *src2) __ksym;

+void bpf_rcu_read_lock(void) __ksym;
+void bpf_rcu_read_unlock(void) __ksym;
+
static inline const struct cpumask *cast(struct bpf_cpumask *cpumask)
{
return (const struct cpumask *)cpumask;
diff --git a/tools/testing/selftests/bpf/progs/cpumask_failure.c b/tools/testing/selftests/bpf/progs/cpumask_failure.c
index cfe83f0ef9e2..9f726d55f747 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_failure.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_failure.c
@@ -127,3 +127,65 @@ int BPF_PROG(test_cpumask_null, struct task_struct *task, u64 clone_flags)

return 0;
}
+
+SEC("tp_btf/task_newtask")
+__failure __msg("R2 must be a rcu pointer")
+int BPF_PROG(test_global_mask_out_of_rcu, struct task_struct *task, u64 clone_flags)
+{
+ struct bpf_cpumask *local, *prev;
+
+ local = create_cpumask();
+ if (!local)
+ return 0;
+
+ prev = bpf_kptr_xchg(&global_mask, local);
+ if (prev) {
+ bpf_cpumask_release(prev);
+ err = 3;
+ return 0;
+ }
+
+ bpf_rcu_read_lock();
+ local = global_mask;
+ if (!local) {
+ err = 4;
+ bpf_rcu_read_unlock();
+ return 0;
+ }
+
+ bpf_rcu_read_unlock();
+
+ /* RCU region is exited before calling KF_RCU kfunc. */
+
+ bpf_cpumask_test_cpu(0, (const struct cpumask *)local);
+
+ return 0;
+}
+
+SEC("tp_btf/task_newtask")
+__failure __msg("NULL pointer passed to trusted arg1")
+int BPF_PROG(test_global_mask_no_null_check, struct task_struct *task, u64 clone_flags)
+{
+ struct bpf_cpumask *local, *prev;
+
+ local = create_cpumask();
+ if (!local)
+ return 0;
+
+ prev = bpf_kptr_xchg(&global_mask, local);
+ if (prev) {
+ bpf_cpumask_release(prev);
+ err = 3;
+ return 0;
+ }
+
+ bpf_rcu_read_lock();
+ local = global_mask;
+
+ /* No NULL check is performed on global cpumask kptr. */
+ bpf_cpumask_test_cpu(0, (const struct cpumask *)local);
+
+ bpf_rcu_read_unlock();
+
+ return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/cpumask_success.c b/tools/testing/selftests/bpf/progs/cpumask_success.c
index 97ed08c4ff03..fe928ff72a06 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_success.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_success.c
@@ -423,3 +423,36 @@ int BPF_PROG(test_insert_kptr_get_release, struct task_struct *task, u64 clone_f

return 0;
}
+
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_global_mask_rcu, struct task_struct *task, u64 clone_flags)
+{
+ struct bpf_cpumask *local, *prev;
+
+ if (!is_test_task())
+ return 0;
+
+ local = create_cpumask();
+ if (!local)
+ return 0;
+
+ prev = bpf_kptr_xchg(&global_mask, local);
+ if (prev) {
+ bpf_cpumask_release(prev);
+ err = 3;
+ return 0;
+ }
+
+ bpf_rcu_read_lock();
+ local = global_mask;
+ if (!local) {
+ err = 4;
+ bpf_rcu_read_unlock();
+ return 0;
+ }
+
+ bpf_cpumask_test_cpu(0, (const struct cpumask *)local);
+ bpf_rcu_read_unlock();
+
+ return 0;
+}
--
2.39.0