netdev - [PATCH v2 bpf-next 4/4] selftests/bpf: Add test for bpf_ksym

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Date:   Fri, 17 Mar 2023 13:19:20 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     davem@...emloft.net
Cc:     daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org,
        void@...ifault.com, davemarchevsky@...a.com, tj@...nel.org,
        memxor@...il.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...com
Subject: [PATCH v2 bpf-next 4/4] selftests/bpf: Add test for bpf_ksym_exists().

From: Alexei Starovoitov <ast@...nel.org>

Add load and run time test for bpf_ksym_exists() and check that the verifier
performs dead code elimination for non-existing kfunc.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Reviewed-by: Martin KaFai Lau <martin.lau@...nel.org>
Acked-by: John Fastabend <john.fastabend@...il.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 .../selftests/bpf/progs/task_kfunc_success.c  | 20 ++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/task_kfunc_success.c b/tools/testing/selftests/bpf/progs/task_kfunc_success.c
index 4f61596b0242..cfa7f12b84e8 100644
--- a/tools/testing/selftests/bpf/progs/task_kfunc_success.c
+++ b/tools/testing/selftests/bpf/progs/task_kfunc_success.c
@@ -17,6 +17,10 @@ int err, pid;
  *         TP_PROTO(struct task_struct *p, u64 clone_flags)
  */
 
+struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym __weak;
+void invalid_kfunc(void) __ksym __weak;
+void bpf_testmod_test_mod_kfunc(int i) __ksym __weak;
+
 static bool is_test_kfunc_task(void)
 {
 	int cur_pid = bpf_get_current_pid_tgid() >> 32;
@@ -26,7 +30,21 @@ static bool is_test_kfunc_task(void)
 
 static int test_acquire_release(struct task_struct *task)
 {
-	struct task_struct *acquired;
+	struct task_struct *acquired = NULL;
+
+	if (!bpf_ksym_exists(bpf_task_acquire)) {
+		err = 3;
+		return 0;
+	}
+	if (!bpf_ksym_exists(bpf_testmod_test_mod_kfunc)) {
+		err = 4;
+		return 0;
+	}
+	if (bpf_ksym_exists(invalid_kfunc)) {
+		/* the verifier's dead code elimination should remove this */
+		err = 5;
+		asm volatile ("goto -1"); /* for (;;); */
+	}
 
 	acquired = bpf_task_acquire(task);
 	bpf_task_release(acquired);
-- 
2.34.1