Re: [PATCH v5 bpf-next 08/17] bpf: Add bpf_core_add_cands() and wire it into bpf_core_apply_relo_insn().

On Wed, Dec 1, 2021 at 10:11 AM Alexei Starovoitov
[off-list ref] wrote:

From: Alexei Starovoitov <ast@kernel.org>

Given BPF program's BTF root type name perform the following steps:
. search in vmlinux candidate cache.
. if (present in cache and candidate list >= 1) return candidate list.
. do a linear search through kernel BTFs for possible candidates.
. regardless of number of candidates found populate vmlinux cache.
. if (candidate list >= 1) return candidate list.
. search in module candidate cache.
. if (present in cache) return candidate list (even if list is empty).
. do a linear search through BTFs of all kernel modules
  collecting candidates from all of them.
. regardless of number of candidates found populate module cache.
. return candidate list.
Then wire the result into bpf_core_apply_relo_insn().

When BPF program is trying to CO-RE relocate a type
that doesn't exist in either vmlinux BTF or in modules BTFs
these steps will perform 2 cache lookups when cache is hit.

Note the cache doesn't prevent the abuse by the program that might
have lots of relocations that cannot be resolved. Hence cond_resched().

CO-RE in the kernel requires CAP_BPF, since BTF loading requires it.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---

Looks correct as far as I can tell.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

 kernel/bpf/btf.c | 346 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 345 insertions(+), 1 deletion(-)

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