On Fri, Nov 19, 2021 at 7:33 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Given BPF program's BTF perform a linear search through kernel BTFs for
> a possible candidate.
> Then wire the result into bpf_core_apply_relo_insn().
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> ---
> kernel/bpf/btf.c | 136 ++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 135 insertions(+), 1 deletion(-)
>
[...]
> int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
> int relo_idx, void *insn)
> {
> - return -EOPNOTSUPP;
> + if (relo->kind != BPF_CORE_TYPE_ID_LOCAL) {
> + struct bpf_core_cand_list *cands;
> +
> + cands = bpf_core_find_cands(ctx, relo->type_id);
this is wrong for many reasons:
1. you will overwrite previous ctx->cands, if it was already set,
which leaks memory
2. this list of candidates should be keyed by relo->type_id ("root
type"). Different root types get their own independent lists; so it
has to be some sort of look up table from type_id to a list of
candidates.
2) means that if you had a bunch of relos against struct task_struct,
you'll crate a list of candidates when processing first relo that
starts at task_struct. All the subsequent relos that have task_struct
as root type will re-used that list and potentially trim it down. If
there are some other relos against, say, struct mm_struct, they will
have their independent list of candidates.
> + if (IS_ERR(cands)) {
> + bpf_log(ctx->log, "target candidate search failed for %d\n",
> + relo->type_id);
> + return PTR_ERR(cands);
> + }
> + ctx->cands = cands;
> + }
> + return bpf_core_apply_relo_insn((void *)ctx->log, insn, relo->insn_off / 8,
> + relo, relo_idx, ctx->btf, ctx->cands);
> }
> --
> 2.30.2
>
