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Date: Fri, 10 May 2019 14:36:00 -0700
From: Stanislav Fomichev <sdf@...ichev.me>
To: Andrii Nakryiko <andriin@...com>
Cc: andrii.nakryiko@...il.com, kernel-team@...com,
netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...com,
yhs@...com, daniel@...earbox.net
Subject: Re: [PATCH v3 bpf] libbpf: detect supported kernel BTF features and
sanitize BTF
On 05/10, Andrii Nakryiko wrote:
> Depending on used versions of libbpf, Clang, and kernel, it's possible to
> have valid BPF object files with valid BTF information, that still won't
> load successfully due to Clang emitting newer BTF features (e.g.,
> BTF_KIND_FUNC, .BTF.ext's line_info/func_info, BTF_KIND_DATASEC, etc), that
> are not yet supported by older kernel.
>
> This patch adds detection of BTF features and sanitizes BPF object's BTF
> by substituting various supported BTF kinds, which have compatible layout:
> - BTF_KIND_FUNC -> BTF_KIND_TYPEDEF
> - BTF_KIND_FUNC_PROTO -> BTF_KIND_ENUM
> - BTF_KIND_VAR -> BTF_KIND_INT
> - BTF_KIND_DATASEC -> BTF_KIND_STRUCT
>
> Replacement is done in such a way as to preserve as much information as
> possible (names, sizes, etc) where possible without violating kernel's
> validation rules.
>
> v2->v3:
> - remove duplicate #defines from libbpf_util.h
>
> v1->v2:
> - add internal libbpf_internal.h w/ common stuff
How is libbpf_internal.h different from libbpf_util.h? libbpf_util.h
looks pretty "internal" to me. Maybe use that one instead?
> - switch SK storage BTF to use new libbpf__probe_raw_btf()
>
> Reported-by: Alexei Starovoitov <ast@...com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> tools/lib/bpf/libbpf.c | 130 +++++++++++++++++++++++++++++++-
> tools/lib/bpf/libbpf_internal.h | 27 +++++++
> tools/lib/bpf/libbpf_probes.c | 73 ++++++++++--------
> 3 files changed, 197 insertions(+), 33 deletions(-)
> create mode 100644 tools/lib/bpf/libbpf_internal.h
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 11a65db4b93f..7e3b79d7c25f 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -44,6 +44,7 @@
> #include "btf.h"
> #include "str_error.h"
> #include "libbpf_util.h"
> +#include "libbpf_internal.h"
>
> #ifndef EM_BPF
> #define EM_BPF 247
> @@ -128,6 +129,10 @@ struct bpf_capabilities {
> __u32 name:1;
> /* v5.2: kernel support for global data sections. */
> __u32 global_data:1;
> + /* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */
> + __u32 btf_func:1;
> + /* BTF_KIND_VAR and BTF_KIND_DATASEC support */
> + __u32 btf_datasec:1;
> };
>
> /*
> @@ -1021,6 +1026,74 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
> return false;
> }
>
> +static void bpf_object__sanitize_btf(struct bpf_object *obj)
> +{
> + bool has_datasec = obj->caps.btf_datasec;
> + bool has_func = obj->caps.btf_func;
> + struct btf *btf = obj->btf;
> + struct btf_type *t;
> + int i, j, vlen;
> + __u16 kind;
> +
> + if (!obj->btf || (has_func && has_datasec))
> + return;
> +
> + for (i = 1; i <= btf__get_nr_types(btf); i++) {
> + t = (struct btf_type *)btf__type_by_id(btf, i);
> + kind = BTF_INFO_KIND(t->info);
> +
> + if (!has_datasec && kind == BTF_KIND_VAR) {
> + /* replace VAR with INT */
> + t->info = BTF_INFO_ENC(BTF_KIND_INT, 0, 0);
> + t->size = sizeof(int);
> + *(int *)(t+1) = BTF_INT_ENC(0, 0, 32);
> + } else if (!has_datasec && kind == BTF_KIND_DATASEC) {
> + /* replace DATASEC with STRUCT */
> + struct btf_var_secinfo *v = (void *)(t + 1);
> + struct btf_member *m = (void *)(t + 1);
> + struct btf_type *vt;
> + char *name;
> +
> + name = (char *)btf__name_by_offset(btf, t->name_off);
> + while (*name) {
> + if (*name == '.')
> + *name = '_';
> + name++;
> + }
> +
> + vlen = BTF_INFO_VLEN(t->info);
> + t->info = BTF_INFO_ENC(BTF_KIND_STRUCT, 0, vlen);
> + for (j = 0; j < vlen; j++, v++, m++) {
> + /* order of field assignments is important */
> + m->offset = v->offset * 8;
> + m->type = v->type;
> + /* preserve variable name as member name */
> + vt = (void *)btf__type_by_id(btf, v->type);
> + m->name_off = vt->name_off;
> + }
> + } else if (!has_func && kind == BTF_KIND_FUNC_PROTO) {
> + /* replace FUNC_PROTO with ENUM */
> + vlen = BTF_INFO_VLEN(t->info);
> + t->info = BTF_INFO_ENC(BTF_KIND_ENUM, 0, vlen);
> + t->size = sizeof(__u32); /* kernel enforced */
> + } else if (!has_func && kind == BTF_KIND_FUNC) {
> + /* replace FUNC with TYPEDEF */
> + t->info = BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0);
> + }
> + }
> +}
> +
> +static void bpf_object__sanitize_btf_ext(struct bpf_object *obj)
> +{
> + if (!obj->btf_ext)
> + return;
> +
> + if (!obj->caps.btf_func) {
> + btf_ext__free(obj->btf_ext);
> + obj->btf_ext = NULL;
> + }
> +}
> +
> static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> {
> Elf *elf = obj->efile.elf;
> @@ -1164,8 +1237,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> obj->btf = NULL;
> } else {
> err = btf__finalize_data(obj, obj->btf);
> - if (!err)
> + if (!err) {
> + bpf_object__sanitize_btf(obj);
> err = btf__load(obj->btf);
> + }
> if (err) {
> pr_warning("Error finalizing and loading %s into kernel: %d. Ignored and continue.\n",
> BTF_ELF_SEC, err);
> @@ -1187,6 +1262,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
> BTF_EXT_ELF_SEC,
> PTR_ERR(obj->btf_ext));
> obj->btf_ext = NULL;
> + } else {
> + bpf_object__sanitize_btf_ext(obj);
> }
> }
> }
> @@ -1556,12 +1633,63 @@ bpf_object__probe_global_data(struct bpf_object *obj)
> return 0;
> }
>
> +static int bpf_object__probe_btf_func(struct bpf_object *obj)
> +{
> + const char strs[] = "\0int\0x\0a";
> + /* void x(int a) {} */
> + __u32 types[] = {
> + /* int */
> + BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> + /* FUNC_PROTO */ /* [2] */
> + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 0),
> + BTF_PARAM_ENC(7, 1),
> + /* FUNC x */ /* [3] */
> + BTF_TYPE_ENC(5, BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0), 2),
> + };
> + int res;
> +
> + res = libbpf__probe_raw_btf((char *)types, sizeof(types),
> + strs, sizeof(strs));
> + if (res < 0)
> + return res;
> + if (res > 0)
> + obj->caps.btf_func = 1;
> + return 0;
> +}
> +
> +static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
> +{
> + const char strs[] = "\0x\0.data";
> + /* static int a; */
> + __u32 types[] = {
> + /* int */
> + BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> + /* VAR x */ /* [2] */
> + BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
> + BTF_VAR_STATIC,
> + /* DATASEC val */ /* [3] */
> + BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
> + BTF_VAR_SECINFO_ENC(2, 0, 4),
> + };
> + int res;
> +
> + res = libbpf__probe_raw_btf((char *)types, sizeof(types),
> + strs, sizeof(strs));
> + if (res < 0)
> + return res;
> + if (res > 0)
> + obj->caps.btf_datasec = 1;
> + return 0;
> +}
> +
> static int
> bpf_object__probe_caps(struct bpf_object *obj)
> {
> int (*probe_fn[])(struct bpf_object *obj) = {
> bpf_object__probe_name,
> bpf_object__probe_global_data,
> + bpf_object__probe_btf_func,
> + bpf_object__probe_btf_datasec,
> };
> int i, ret;
>
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> new file mode 100644
> index 000000000000..789e435b5900
> --- /dev/null
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
> +
> +/*
> + * Internal libbpf helpers.
> + *
> + * Copyright (c) 2019 Facebook
> + */
> +
> +#ifndef __LIBBPF_LIBBPF_INTERNAL_H
> +#define __LIBBPF_LIBBPF_INTERNAL_H
> +
> +#define BTF_INFO_ENC(kind, kind_flag, vlen) \
> + ((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
> +#define BTF_TYPE_ENC(name, info, size_or_type) (name), (info), (size_or_type)
> +#define BTF_INT_ENC(encoding, bits_offset, nr_bits) \
> + ((encoding) << 24 | (bits_offset) << 16 | (nr_bits))
> +#define BTF_TYPE_INT_ENC(name, encoding, bits_offset, bits, sz) \
> + BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_INT, 0, 0), sz), \
> + BTF_INT_ENC(encoding, bits_offset, bits)
> +#define BTF_MEMBER_ENC(name, type, bits_offset) (name), (type), (bits_offset)
> +#define BTF_PARAM_ENC(name, type) (name), (type)
> +#define BTF_VAR_SECINFO_ENC(type, offset, size) (type), (offset), (size)
> +
> +int libbpf__probe_raw_btf(const char *raw_types, size_t types_len,
> + const char *str_sec, size_t str_len);
> +
> +#endif /* __LIBBPF_LIBBPF_INTERNAL_H */
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index a2c64a9ce1a6..5e2aa83f637a 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -15,6 +15,7 @@
>
> #include "bpf.h"
> #include "libbpf.h"
> +#include "libbpf_internal.h"
>
> static bool grep(const char *buffer, const char *pattern)
> {
> @@ -132,21 +133,43 @@ bool bpf_probe_prog_type(enum bpf_prog_type prog_type, __u32 ifindex)
> return errno != EINVAL && errno != EOPNOTSUPP;
> }
>
> -static int load_btf(void)
> +int libbpf__probe_raw_btf(const char *raw_types, size_t types_len,
> + const char *str_sec, size_t str_len)
> {
> -#define BTF_INFO_ENC(kind, kind_flag, vlen) \
> - ((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
> -#define BTF_TYPE_ENC(name, info, size_or_type) \
> - (name), (info), (size_or_type)
> -#define BTF_INT_ENC(encoding, bits_offset, nr_bits) \
> - ((encoding) << 24 | (bits_offset) << 16 | (nr_bits))
> -#define BTF_TYPE_INT_ENC(name, encoding, bits_offset, bits, sz) \
> - BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_INT, 0, 0), sz), \
> - BTF_INT_ENC(encoding, bits_offset, bits)
> -#define BTF_MEMBER_ENC(name, type, bits_offset) \
> - (name), (type), (bits_offset)
> -
> - const char btf_str_sec[] = "\0bpf_spin_lock\0val\0cnt\0l";
> + struct btf_header hdr = {
> + .magic = BTF_MAGIC,
> + .version = BTF_VERSION,
> + .hdr_len = sizeof(struct btf_header),
> + .type_len = types_len,
> + .str_off = types_len,
> + .str_len = str_len,
> + };
> + int btf_fd, btf_len;
> + __u8 *raw_btf;
> +
> + btf_len = hdr.hdr_len + hdr.type_len + hdr.str_len;
> + raw_btf = malloc(btf_len);
> + if (!raw_btf)
> + return -ENOMEM;
> +
> + memcpy(raw_btf, &hdr, sizeof(hdr));
> + memcpy(raw_btf + hdr.hdr_len, raw_types, hdr.type_len);
> + memcpy(raw_btf + hdr.hdr_len + hdr.type_len, str_sec, hdr.str_len);
> +
> + btf_fd = bpf_load_btf(raw_btf, btf_len, NULL, 0, false);
> + if (btf_fd < 0) {
> + free(raw_btf);
> + return 0;
> + }
> +
> + close(btf_fd);
> + free(raw_btf);
> + return 1;
> +}
> +
> +static int load_sk_storage_btf(void)
> +{
> + const char strs[] = "\0bpf_spin_lock\0val\0cnt\0l";
> /* struct bpf_spin_lock {
> * int val;
> * };
> @@ -155,7 +178,7 @@ static int load_btf(void)
> * struct bpf_spin_lock l;
> * };
> */
> - __u32 btf_raw_types[] = {
> + __u32 types[] = {
> /* int */
> BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
> /* struct bpf_spin_lock */ /* [2] */
> @@ -166,23 +189,9 @@ static int load_btf(void)
> BTF_MEMBER_ENC(19, 1, 0), /* int cnt; */
> BTF_MEMBER_ENC(23, 2, 32),/* struct bpf_spin_lock l; */
> };
> - struct btf_header btf_hdr = {
> - .magic = BTF_MAGIC,
> - .version = BTF_VERSION,
> - .hdr_len = sizeof(struct btf_header),
> - .type_len = sizeof(btf_raw_types),
> - .str_off = sizeof(btf_raw_types),
> - .str_len = sizeof(btf_str_sec),
> - };
> - __u8 raw_btf[sizeof(struct btf_header) + sizeof(btf_raw_types) +
> - sizeof(btf_str_sec)];
> -
> - memcpy(raw_btf, &btf_hdr, sizeof(btf_hdr));
> - memcpy(raw_btf + sizeof(btf_hdr), btf_raw_types, sizeof(btf_raw_types));
> - memcpy(raw_btf + sizeof(btf_hdr) + sizeof(btf_raw_types),
> - btf_str_sec, sizeof(btf_str_sec));
>
> - return bpf_load_btf(raw_btf, sizeof(raw_btf), 0, 0, 0);
> + return libbpf__probe_raw_btf((char *)types, sizeof(types),
> + strs, sizeof(strs));
> }
>
> bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex)
> @@ -222,7 +231,7 @@ bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex)
> value_size = 8;
> max_entries = 0;
> map_flags = BPF_F_NO_PREALLOC;
> - btf_fd = load_btf();
> + btf_fd = load_sk_storage_btf();
> if (btf_fd < 0)
> return false;
> break;
> --
> 2.17.1
>
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