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Message-ID: <CAHap4zv=-YV6oXdncZW9DRaBu16b6-81HXretRX-orL2d=B4sQ@mail.gmail.com>
Date: Tue, 16 Nov 2021 14:23:59 -0500
From: Mauricio Vásquez Bernal <mauricio@...volk.io>
To: Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Rafael David Tinoco <rafaeldtinoco@...il.com>,
Lorenzo Fontana <lorenzo.fontana@...stic.co>,
Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v2 3/4] libbpf: Introduce 'bpf_object__prepare()'
On Tue, Nov 16, 2021 at 11:42 AM Mauricio Vásquez <mauricio@...volk.io> wrote:
>
> BTFGen[0] requires access to the result of the CO-RE relocations without
> actually loading the bpf programs. The current libbpf API doesn't allow
> it because all the object preparation (subprogs, relocations: co-re,
> elf, maps) happens inside bpf_object__load().
>
> This commit introduces a new bpf_object__prepare() function to perform
> all the preparation steps than an ebpf object requires, allowing users
> to access the result of those preparation steps without having to load
> the program. Almost all the steps that were done in bpf_object__load()
> are now done in bpf_object__prepare(), except map creation and program
> loading.
>
> Map relocations require a bit more attention as maps are only created in
> bpf_object__load(). For this reason bpf_object__prepare() relocates maps
> using BPF_PSEUDO_MAP_IDX, if someone dumps the instructions before
> loading the program they get something meaningful. Map relocations are
> completed in bpf_object__load() once the maps are created and we have
> their fd to use with BPF_PSEUDO_MAP_FD.
>
> Users won’t see any visible changes if they’re using bpf_object__open()
> + bpf_object__load() because this commit keeps backwards compatibility
> by calling bpf_object__prepare() in bpf_object_load() if it wasn’t
> called by the user.
>
> bpf_object__prepare_xattr() is not implemented as their counterpart
> bpf_object__load_xattr() will be deprecated[1]. New options will be
> added only to bpf_object_open_opts.
>
> [0]: https://github.com/kinvolk/btfgen/
> [1]: https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#libbpfh-high-level-apis
>
> Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> ---
> tools/lib/bpf/libbpf.c | 130 ++++++++++++++++++++++++++++-----------
> tools/lib/bpf/libbpf.h | 2 +
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 98 insertions(+), 35 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6ca76365c6da..f50f9428bb03 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -514,6 +514,7 @@ struct bpf_object {
> int nr_extern;
> int kconfig_map_idx;
>
> + bool prepared;
> bool loaded;
> bool has_subcalls;
> bool has_rodata;
> @@ -5576,34 +5577,19 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
>
> switch (relo->type) {
> case RELO_LD64:
> - if (obj->gen_loader) {
> - insn[0].src_reg = BPF_PSEUDO_MAP_IDX;
> - insn[0].imm = relo->map_idx;
> - } else {
> - insn[0].src_reg = BPF_PSEUDO_MAP_FD;
> - insn[0].imm = obj->maps[relo->map_idx].fd;
> - }
> + insn[0].src_reg = BPF_PSEUDO_MAP_IDX;
> + insn[0].imm = relo->map_idx;
> break;
> case RELO_DATA:
> insn[1].imm = insn[0].imm + relo->sym_off;
> - if (obj->gen_loader) {
> - insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
> - insn[0].imm = relo->map_idx;
> - } else {
> - insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
> - insn[0].imm = obj->maps[relo->map_idx].fd;
> - }
> + insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
> + insn[0].imm = relo->map_idx;
> break;
> case RELO_EXTERN_VAR:
> ext = &obj->externs[relo->sym_off];
> if (ext->type == EXT_KCFG) {
> - if (obj->gen_loader) {
> - insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
> - insn[0].imm = obj->kconfig_map_idx;
> - } else {
> - insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
> - insn[0].imm = obj->maps[obj->kconfig_map_idx].fd;
> - }
> + insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
> + insn[0].imm = obj->kconfig_map_idx;
> insn[1].imm = ext->kcfg.data_off;
> } else /* EXT_KSYM */ {
> if (ext->ksym.type_id && ext->is_set) { /* typed ksyms */
> @@ -6144,8 +6130,50 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
> return err;
> }
> }
> - if (!obj->gen_loader)
> - bpf_object__free_relocs(obj);
> +
> + return 0;
> +}
> +
> +/* relocate instructions that refer to map fds */
> +static int
> +bpf_object__finish_relocate(struct bpf_object *obj)
> +{
> + int i, j;
> +
> + if (obj->gen_loader)
> + return 0;
> +
> + for (i = 0; i < obj->nr_programs; i++) {
> + struct bpf_program *prog = &obj->programs[i];
> +
> + if (prog_is_subprog(obj, prog))
> + continue;
> + for (j = 0; j < prog->nr_reloc; j++) {
> + struct reloc_desc *relo = &prog->reloc_desc[j];
> + struct bpf_insn *insn = &prog->insns[relo->insn_idx];
> + struct extern_desc *ext;
> +
> + switch (relo->type) {
> + case RELO_LD64:
> + insn[0].src_reg = BPF_PSEUDO_MAP_FD;
> + insn[0].imm = obj->maps[relo->map_idx].fd;
> + break;
> + case RELO_DATA:
> + insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
> + insn[0].imm = obj->maps[relo->map_idx].fd;
> + break;
> + case RELO_EXTERN_VAR:
> + ext = &obj->externs[relo->sym_off];
> + if (ext->type == EXT_KCFG) {
> + insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
> + insn[0].imm = obj->maps[obj->kconfig_map_idx].fd;
> + }
> + default:
> + break;
> + }
> + }
> + }
> +
> return 0;
> }
>
> @@ -6706,8 +6734,8 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
> if (err)
> return err;
> }
> - if (obj->gen_loader)
> - bpf_object__free_relocs(obj);
> +
> + bpf_object__free_relocs(obj);
> return 0;
> }
>
> @@ -7258,6 +7286,39 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
> return 0;
> }
>
> +static int __bpf_object__prepare(struct bpf_object *obj, int log_level,
> + const char *target_btf_path)
> +{
> + int err;
> +
> + if (obj->prepared) {
> + pr_warn("object '%s': prepare can't be attempted twice\n", obj->name);
> + return libbpf_err(-EINVAL);
> + }
> +
> + if (obj->gen_loader)
> + bpf_gen__init(obj->gen_loader, log_level);
> +
> + err = bpf_object__probe_loading(obj);
> + err = err ? : bpf_object__load_vmlinux_btf(obj, false);
> + err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
> + err = err ? : bpf_object__sanitize_and_load_btf(obj);
> + err = err ? : bpf_object__sanitize_maps(obj);
> + err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
> + err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);
> +
> + obj->prepared = true;
> +
> + return err;
> +}
> +
> +LIBBPF_API int bpf_object__prepare(struct bpf_object *obj)
> +{
> + if (!obj)
> + return libbpf_err(-EINVAL);
> + return __bpf_object__prepare(obj, 0, NULL);
> +}
> +
> int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
> {
> struct bpf_object *obj;
> @@ -7274,17 +7335,14 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
> return libbpf_err(-EINVAL);
> }
>
> - if (obj->gen_loader)
> - bpf_gen__init(obj->gen_loader, attr->log_level);
> + if (!obj->prepared) {
> + err = __bpf_object__prepare(obj, attr->log_level, attr->target_btf_path);
> + if (err)
> + return err;
> + }
>
> - err = bpf_object__probe_loading(obj);
After sending the patches we realized they weren't working without
root privileges in systems with unprivileged BPF disabled. This line
should not be moved to bpf_object__prepare indeed. We'll fix it in the
next iteration.
> - err = err ? : bpf_object__load_vmlinux_btf(obj, false);
> - err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
> - err = err ? : bpf_object__sanitize_and_load_btf(obj);
> - err = err ? : bpf_object__sanitize_maps(obj);
> - err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
> - err = err ? : bpf_object__create_maps(obj);
> - err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : attr->target_btf_path);
> + err = bpf_object__create_maps(obj);
> + err = err ? : bpf_object__finish_relocate(obj);
> err = err ? : bpf_object__load_progs(obj, attr->log_level);
>
> if (obj->gen_loader) {
> @@ -7940,6 +7998,8 @@ void bpf_object__close(struct bpf_object *obj)
> bpf_object__elf_finish(obj);
> bpf_object_unload(obj);
> btf__free(obj->btf);
> + if (!obj->user_provided_btf_vmlinux)
> + btf__free(obj->btf_vmlinux_override);
> btf_ext__free(obj->btf_ext);
>
> for (i = 0; i < obj->nr_maps; i++)
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 908ab04dc9bd..d206b4400a4d 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -148,6 +148,8 @@ LIBBPF_API int bpf_object__unpin_programs(struct bpf_object *obj,
> LIBBPF_API int bpf_object__pin(struct bpf_object *object, const char *path);
> LIBBPF_API void bpf_object__close(struct bpf_object *object);
>
> +LIBBPF_API int bpf_object__prepare(struct bpf_object *obj);
> +
> struct bpf_object_load_attr {
> struct bpf_object *obj;
> int log_level;
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index c9555f8655af..459b41228933 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -415,4 +415,5 @@ LIBBPF_0.6.0 {
> perf_buffer__new_raw;
> perf_buffer__new_raw_deprecated;
> btf__save_raw;
> + bpf_object__prepare;
> } LIBBPF_0.5.0;
> --
> 2.25.1
>
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