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    Subject[PATCH 5.10 115/663] libbpf: Ignore non function pointer member in struct_ops
    Date
    From: Martin KaFai Lau <kafai@fb.com>

    [ Upstream commit d2836dddc95d5dd82c7cb23726c97d8c9147f050 ]

    When libbpf initializes the kernel's struct_ops in
    "bpf_map__init_kern_struct_ops()", it enforces all
    pointer types must be a function pointer and rejects
    others. It turns out to be too strict. For example,
    when directly using "struct tcp_congestion_ops" from vmlinux.h,
    it has a "struct module *owner" member and it is set to NULL
    in a bpf_tcp_cc.o.

    Instead, it only needs to ensure the member is a function
    pointer if it has been set (relocated) to a bpf-prog.
    This patch moves the "btf_is_func_proto(kern_mtype)" check
    after the existing "if (!prog) { continue; }". The original debug
    message in "if (!prog) { continue; }" is also removed since it is
    no longer valid. Beside, there is a later debug message to tell
    which function pointer is set.

    The "btf_is_func_proto(mtype)" has already been guaranteed
    in "bpf_object__collect_st_ops_relos()" which has been run
    before "bpf_map__init_kern_struct_ops()". Thus, this check
    is removed.

    v2:
    - Remove outdated debug message (Andrii)
    Remove because there is a later debug message to tell
    which function pointer is set.
    - Following mtype->type is no longer needed. Remove:
    "skip_mods_and_typedefs(btf, mtype->type, &mtype_id)"
    - Do "if (!prog)" test before skip_mods_and_typedefs.

    Fixes: 590a00888250 ("bpf: libbpf: Add STRUCT_OPS support")
    Signed-off-by: Martin KaFai Lau <kafai@fb.com>
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Acked-by: Andrii Nakryiko <andrii@kernel.org>
    Link: https://lore.kernel.org/bpf/20210212021030.266932-1-kafai@fb.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/lib/bpf/libbpf.c | 22 +++++++++++-----------
    1 file changed, 11 insertions(+), 11 deletions(-)

    diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
    index ad165e6e74bc0..b954db52bb807 100644
    --- a/tools/lib/bpf/libbpf.c
    +++ b/tools/lib/bpf/libbpf.c
    @@ -865,24 +865,24 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map,
    if (btf_is_ptr(mtype)) {
    struct bpf_program *prog;

    - mtype = skip_mods_and_typedefs(btf, mtype->type, &mtype_id);
    + prog = st_ops->progs[i];
    + if (!prog)
    + continue;
    +
    kern_mtype = skip_mods_and_typedefs(kern_btf,
    kern_mtype->type,
    &kern_mtype_id);
    - if (!btf_is_func_proto(mtype) ||
    - !btf_is_func_proto(kern_mtype)) {
    - pr_warn("struct_ops init_kern %s: non func ptr %s is not supported\n",
    +
    + /* mtype->type must be a func_proto which was
    + * guaranteed in bpf_object__collect_st_ops_relos(),
    + * so only check kern_mtype for func_proto here.
    + */
    + if (!btf_is_func_proto(kern_mtype)) {
    + pr_warn("struct_ops init_kern %s: kernel member %s is not a func ptr\n",
    map->name, mname);
    return -ENOTSUP;
    }

    - prog = st_ops->progs[i];
    - if (!prog) {
    - pr_debug("struct_ops init_kern %s: func ptr %s is not set\n",
    - map->name, mname);
    - continue;
    - }
    -
    prog->attach_btf_id = kern_type_id;
    prog->expected_attach_type = kern_member_idx;

    --
    2.27.0


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