[PATCH bpf 06/11] selftests/bpf: Test rejection of pkt args to mutating subprogs

[Emil Tsalapatis <emil@etsalapatis.com>]

Add a selftests that ensures that PTR_TO_PACKET arguments can
only be passed to subprogs that will never adjust the underlying
packet memory, and are rejected otherwise.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 .../bpf/progs/verifier_global_ptr_args.c      | 53 +++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c b/tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c
index b277b1efb..10019af5e 100644
--- a/tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c
+++ b/tools/testing/selftests/bpf/progs/verifier_global_ptr_args.c
@@ -350,4 +350,57 @@ int anything_to_untrusted_mem(void *ctx)
 	return 0;
 }
 
+struct pkt_arg {
+	__u64 x;
+	__u8 pad[56];
+};
+
+__weak int subprog_pkt_ptr_no_change(struct pkt_arg *p)
+{
+	if (!p)
+		return 0;
+
+	return p->x;
+}
+
+SEC("?tc")
+__success
+int pkt_ptr_to_global_mem_arg_no_change(struct __sk_buff *skb)
+{
+	void *data = (void *)(long)skb->data;
+	void *data_end = (void *)(long)skb->data_end;
+	struct pkt_arg *p = data;
+
+	if ((void *)(p + 1) > data_end)
+		return 0;
+
+	return subprog_pkt_ptr_no_change(p);
+}
+
+__weak int subprog_pkt_ptr_changes_data(struct __sk_buff *skb __arg_ctx,
+					struct pkt_arg *p)
+{
+	if (!p)
+		return 0;
+
+	bpf_skb_pull_data(skb, 0);
+	return p->x;
+}
+
+SEC("?tc")
+__failure __log_level(2)
+__msg("R2 is a packet pointer, but func#{{[0-9]+}} may change packet data")
+__msg("Caller passes invalid args into func#{{[0-9]+}} ('subprog_pkt_ptr_changes_data')")
+int pkt_ptr_to_global_mem_arg_changes_data(struct __sk_buff *skb)
+{
+	void *data = (void *)(long)skb->data;
+	void *data_end = (void *)(long)skb->data_end;
+	struct pkt_arg *p = data;
+
+	if ((void *)(p + 1) > data_end)
+		return 0;
+
+	return subprog_pkt_ptr_changes_data(skb, p);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.54.0