From 861544b5274508ffd40f67678cb8e974631b520a Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Date: Tue, 29 Sep 2020 14:45:52 +0200 Subject: [PATCH] UPSTREAM: bpf: Fix context type resolving for extension programs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Eelco reported we can't properly access arguments if the tracing program is attached to extension program. Having following program: SEC("classifier/test_pkt_md_access") int test_pkt_md_access(struct __sk_buff *skb) with its extension: SEC("freplace/test_pkt_md_access") int test_pkt_md_access_new(struct __sk_buff *skb) and tracing that extension with: SEC("fentry/test_pkt_md_access_new") int BPF_PROG(fentry, struct sk_buff *skb) It's not possible to access skb argument in the fentry program, with following error from verifier: ; int BPF_PROG(fentry, struct sk_buff *skb) 0: (79) r1 = *(u64 *)(r1 +0) invalid bpf_context access off=0 size=8 The problem is that btf_ctx_access gets the context type for the traced program, which is in this case the extension. But when we trace extension program, we want to get the context type of the program that the extension is attached to, so we can access the argument properly in the trace program. This version of the patch is tweaked slightly from Jiri's original one, since the refactoring in the previous patches means we have to get the target prog type from the new variable in prog->aux instead of directly from the target prog. Reported-by: Eelco Chaudron Suggested-by: Jiri Olsa Change-Id: I300379f68e6db9af443aa666d62a66f36746de29 Signed-off-by: Toke Høiland-Jørgensen Signed-off-by: Alexei Starovoitov Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/160138355278.48470.17057040257274725638.stgit@toke.dk --- kernel/bpf/btf.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index bc01dcffa143..f8210880da7a 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -4589,7 +4589,14 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, info->reg_type = PTR_TO_BTF_ID; if (tgt_prog) { - ret = btf_translate_to_vmlinux(log, btf, t, tgt_prog->type, arg); + enum bpf_prog_type tgt_type; + + if (tgt_prog->type == BPF_PROG_TYPE_EXT) + tgt_type = tgt_prog->aux->saved_dst_prog_type; + else + tgt_type = tgt_prog->type; + + ret = btf_translate_to_vmlinux(log, btf, t, tgt_type, arg); if (ret > 0) { info->btf_id = ret; return true;