From: Paul Chaignon Date: Wed, 17 Sep 2025 08:10:53 +0000 (+0200) Subject: selftests/bpf: Test accesses to ctx padding X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=180a46bc1a1c585f5187df7bccdb522556f4ecd8;p=users%2Fhch%2Fmisc.git selftests/bpf: Test accesses to ctx padding This patch adds tests covering the various paddings in ctx structures. In case of sk_lookup BPF programs, the behavior is a bit different because accesses to the padding are explicitly allowed. Other cases result in a clear reject from the verifier. Signed-off-by: Paul Chaignon Signed-off-by: Daniel Borkmann Acked-by: Eduard Zingerman Acked-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/3dc5f025e350aeb2bb1c257b87c577518e574aeb.1758094761.git.paul.chaignon@gmail.com --- diff --git a/tools/testing/selftests/bpf/progs/verifier_ctx.c b/tools/testing/selftests/bpf/progs/verifier_ctx.c index b927906aa305..5ebf7d9bcc55 100644 --- a/tools/testing/selftests/bpf/progs/verifier_ctx.c +++ b/tools/testing/selftests/bpf/progs/verifier_ctx.c @@ -262,4 +262,34 @@ narrow_load("sockops", bpf_sock_ops, skb_hwtstamp); unaligned_access("flow_dissector", __sk_buff, data); unaligned_access("netfilter", bpf_nf_ctx, skb); +#define padding_access(type, ctx, prev_field, sz) \ + SEC(type) \ + __description("access on " #ctx " padding after " #prev_field) \ + __naked void padding_ctx_access_##ctx(void) \ + { \ + asm volatile (" \ + r1 = *(u%[size] *)(r1 + %[off]); \ + r0 = 0; \ + exit;" \ + : \ + : __imm_const(size, sz * 8), \ + __imm_const(off, offsetofend(struct ctx, prev_field)) \ + : __clobber_all); \ + } + +__failure __msg("invalid bpf_context access") +padding_access("cgroup/bind4", bpf_sock_addr, msg_src_ip6[3], 4); + +__success +padding_access("sk_lookup", bpf_sk_lookup, remote_port, 2); + +__failure __msg("invalid bpf_context access") +padding_access("tc", __sk_buff, tstamp_type, 2); + +__failure __msg("invalid bpf_context access") +padding_access("cgroup/post_bind4", bpf_sock, dst_port, 2); + +__failure __msg("invalid bpf_context access") +padding_access("sk_reuseport", sk_reuseport_md, hash, 4); + char _license[] SEC("license") = "GPL";