On Sat, Sep 19, 2020 at 4:50 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
>
> 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 <echaudro@xxxxxxxxxx>
> Suggested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> kernel/bpf/btf.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
[...]
