Merge: bpf: Reject bpf_timer for PREEMPT_RT

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7405

JIRA: https://issues.redhat.com/browse/RHEL-83826

Omitted-fix: f7528e4 ("selftests/bpf: Skip timer cases when bpf_timer is not supported")
- The fix skips a selftest introduced in 88a3bde ("selftests/bpf: Add case to test bpf_in_interrupt()")
which has not been backported.

Selftests cause kernel hang on RT kernels due to bpf_timer.
This patch rejects bpf_timer usage in the verifier when
PREEMPT_RT is enabled, and skips the corresponding timer selftests.

Signed-off-by: Gregory Bell <grbell@redhat.com>

Approved-by: Viktor Malik <vmalik@redhat.com>
Approved-by: Jerome Marchand <jmarchan@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

kernel/bpf/verifier.c

@@ -7779,6 +7779,10 @@ static int process_timer_func(struct bpf_verifier_env *env, int regno,
 		verbose(env, "verifier bug. Two map pointers in a timer helper\n");
 		return -EFAULT;
 	}
+	if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+		verbose(env, "bpf_timer cannot be used for PREEMPT_RT.\n");
+		return -EOPNOTSUPP;
+	}
 	meta->map_uid = reg->map_uid;
 	meta->map_ptr = map;
 	return 0;

tools/testing/selftests/bpf/prog_tests/free_timer.c

@@ -124,6 +124,10 @@ void test_free_timer(void)
 	int err;
 
 	skel = free_timer__open_and_load();
+	if (!skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(skel, "open_load"))
 		return;
 

tools/testing/selftests/bpf/prog_tests/timer.c

@@ -86,6 +86,10 @@ void serial_test_timer(void)
 	int err;
 
 	timer_skel = timer__open_and_load();
+	if (!timer_skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(timer_skel, "timer_skel_load"))
 		return;
 

tools/testing/selftests/bpf/prog_tests/timer_crash.c

@@ -12,6 +12,10 @@ static void test_timer_crash_mode(int mode)
 	struct timer_crash *skel;
 
 	skel = timer_crash__open_and_load();
+	if (!skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(skel, "timer_crash__open_and_load"))
 		return;
 	skel->bss->pid = getpid();

tools/testing/selftests/bpf/prog_tests/timer_lockup.c

@@ -59,6 +59,10 @@ void test_timer_lockup(void)
 	}
 
 	skel = timer_lockup__open_and_load();
+	if (!skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(skel, "timer_lockup__open_and_load"))
 		return;
 

tools/testing/selftests/bpf/prog_tests/timer_mim.c

@@ -65,6 +65,10 @@ void serial_test_timer_mim(void)
 		goto cleanup;
 
 	timer_skel = timer_mim__open_and_load();
+	if (!timer_skel && errno == EOPNOTSUPP) {
+		test__skip();
+		return;
+	}
 	if (!ASSERT_OK_PTR(timer_skel, "timer_skel_load"))
 		goto cleanup;