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selftests/bpf: Test accesses to ctx padding

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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 <paul.chaignon@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/3dc5f025e350aeb2bb1c257b87c577518e574aeb.1758094761.git.paul.chaignon@gmail.com
This commit is contained in:
Paul Chaignon 2025-09-17 10:10:53 +02:00 committed by Daniel Borkmann
parent 7c60f6e488
commit 180a46bc1a
1 changed files with 30 additions and 0 deletions
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30
tools/testing/selftests/bpf/progs/verifier_ctx.c
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@ -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";