[PATCH bpf v1 10/10] selftests/bpf: Check syscall helpers in timer callbacks

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

A BPF_PROG_TYPE_SYSCALL program is sleepable, but its bpf_timer callbacks
run in a non-sleepable hrtimer softirq context.

Add verifier cases that call bpf_sys_bpf() and bpf_sys_close() from timer
callbacks. Without the syscall helper prototype annotations these programs
load, so their failure expectations expose the bug.

Also add successful controls that call each helper from the syscall program
main body, ensuring that the intended sleepable use remains accepted.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../bpf/progs/verifier_async_cb_context.c     | 64 +++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_async_cb_context.c b/tools/testing/selftests/bpf/progs/verifier_async_cb_context.c
index 6bf95550a024..a7c84d3fa4c7 100644
--- a/tools/testing/selftests/bpf/progs/verifier_async_cb_context.c
+++ b/tools/testing/selftests/bpf/progs/verifier_async_cb_context.c
@@ -62,6 +62,70 @@ int timer_sleepable_prog(void *ctx)
 	return 0;
 }
 
+static int timer_sys_bpf_cb(void *map, int *key, struct bpf_timer *timer)
+{
+	__u64 attr = 0;
+
+	bpf_sys_bpf(BPF_MAP_FREEZE, &attr, sizeof(attr));
+	return 0;
+}
+
+SEC("syscall")
+__failure __msg("sleepable helper bpf_sys_bpf#{{[0-9]+}} in non-sleepable prog")
+int timer_sys_bpf_prog(void *ctx)
+{
+	struct timer_elem *val;
+	int key = 0;
+
+	val = bpf_map_lookup_elem(&timer_map, &key);
+	if (!val)
+		return 0;
+
+	bpf_timer_init(&val->t, &timer_map, 0);
+	bpf_timer_set_callback(&val->t, timer_sys_bpf_cb);
+	return 0;
+}
+
+static int timer_sys_close_cb(void *map, int *key, struct bpf_timer *timer)
+{
+	bpf_sys_close(0);
+	return 0;
+}
+
+SEC("syscall")
+__failure __msg("sleepable helper bpf_sys_close#{{[0-9]+}} in non-sleepable prog")
+int timer_sys_close_prog(void *ctx)
+{
+	struct timer_elem *val;
+	int key = 0;
+
+	val = bpf_map_lookup_elem(&timer_map, &key);
+	if (!val)
+		return 0;
+
+	bpf_timer_init(&val->t, &timer_map, 0);
+	bpf_timer_set_callback(&val->t, timer_sys_close_cb);
+	return 0;
+}
+
+SEC("syscall")
+__success
+int syscall_sys_bpf_prog(void *ctx)
+{
+	__u64 attr = 0;
+
+	bpf_sys_bpf(BPF_MAP_FREEZE, &attr, sizeof(attr));
+	return 0;
+}
+
+SEC("syscall")
+__success
+int syscall_sys_close_prog(void *ctx)
+{
+	bpf_sys_close(0);
+	return 0;
+}
+
 /* Workqueue tests */
 
 struct wq_elem {
-- 
2.53.0