[PATCH bpf-next v1 09/14] selftests/bpf: Test non-sleepable kfunc context

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Exercise a non-sleepable tracing program that enters an RCU read lock region
before calling a sleepable kfunc. Assert both the legacy verifier message and
the structured reason based on the program's sleepability.

This distinguishes the program-level rejection from the later check for a
sleepable program calling an operation inside an active critical section.

Link: https://lore.kernel.org/bpf/2e42a1a2bf45f4d2aba7495bdc9f147558055740e2f3c8b9dae255f6c57fc13c@mail.kernel.org/
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 tools/testing/selftests/bpf/progs/preempt_lock.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/preempt_lock.c b/tools/testing/selftests/bpf/progs/preempt_lock.c
index 6d5fce7e6ffc..83c911494a34 100644
--- a/tools/testing/selftests/bpf/progs/preempt_lock.c
+++ b/tools/testing/selftests/bpf/progs/preempt_lock.c
@@ -6,6 +6,8 @@
 #include "bpf_experimental.h"
 
 extern int bpf_copy_from_user_str(void *dst, u32 dst__sz, const void *unsafe_ptr__ign, u64 flags) __weak __ksym;
+extern void bpf_rcu_read_lock(void) __ksym;
+extern void bpf_rcu_read_unlock(void) __ksym;
 
 SEC("?tc")
 __failure __msg("BPF_EXIT instruction in main prog cannot be used inside bpf_preempt_disable-ed region")
@@ -127,6 +129,19 @@ int preempt_sleepable_kfunc(void *ctx)
 	return 0;
 }
 
+SEC("?fentry/" SYS_PREFIX "sys_getpgid")
+__failure __msg("program must be sleepable to call sleepable kfunc bpf_copy_from_user_str")
+__msg("cannot be used in non-sleepable program")
+int non_sleepable_kfunc_in_rcu(void *ctx)
+{
+	u32 data;
+
+	bpf_rcu_read_lock();
+	bpf_copy_from_user_str(&data, sizeof(data), NULL, 0);
+	bpf_rcu_read_unlock();
+	return 0;
+}
+
 int __noinline preempt_global_subprog(void)
 {
 	preempt_balance_subprog();
-- 
2.53.0