selftests/bpf: Test invalid narrower ctx load

JIRA: https://issues.redhat.com/browse/RHEL-110274

commit ba578b8
Author: Paul Chaignon <paul.chaignon@gmail.com>
Date:   Tue Jul 22 16:33:37 2025 +0200

    selftests/bpf: Test invalid narrower ctx load

    This patch adds selftests to cover invalid narrower loads on the
    context. These used to cause kernel warnings before the previous patch.
    To trigger the warning, the load had to be aligned, to read an affected
    context field (ex., skb->sk), and not starting at the beginning of the
    field.

    The nine new cases all fail without the previous patch.

    Suggested-by: Eduard Zingerman <eddyz87@gmail.com>
    Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
    Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
    Acked-by: Eduard Zingerman <eddyz87@gmail.com>
    Link: https://patch.msgid.link/44cd83ea9c6868079943f0a436c6efa850528cc1.1753194596.git.paul.chaignon@gmail.com

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Author: viktormalik

tools/testing/selftests/bpf/progs/verifier_ctx.c

@@ -218,4 +218,29 @@ __naked void null_check_8_null_bind(void)
 	: __clobber_all);
 }
 
+#define narrow_load(type, ctx, field)					\
+	SEC(type)							\
+	__description("narrow load on field " #field " of " #ctx)	\
+	__failure __msg("invalid bpf_context access")			\
+	__naked void invalid_narrow_load##ctx##field(void)		\
+	{								\
+		asm volatile ("						\
+		r1 = *(u32 *)(r1 + %[off]);				\
+		r0 = 0;							\
+		exit;"							\
+		:							\
+		: __imm_const(off, offsetof(struct ctx, field) + 4)	\
+		: __clobber_all);					\
+	}
+
+narrow_load("cgroup/getsockopt", bpf_sockopt, sk);
+narrow_load("cgroup/getsockopt", bpf_sockopt, optval);
+narrow_load("cgroup/getsockopt", bpf_sockopt, optval_end);
+narrow_load("tc", __sk_buff, sk);
+narrow_load("cgroup/bind4", bpf_sock_addr, sk);
+narrow_load("sockops", bpf_sock_ops, sk);
+narrow_load("sockops", bpf_sock_ops, skb_data);
+narrow_load("sockops", bpf_sock_ops, skb_data_end);
+narrow_load("sockops", bpf_sock_ops, skb_hwtstamp);
+
 char _license[] SEC("license") = "GPL";