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Message-ID: <CAEf4BzZD1=S0hcg7wj0_LqggcVn_6SDWzy3ZqS=rGbf0Q_s5+Q@mail.gmail.com>
Date: Fri, 10 May 2019 14:38:34 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Stanislav Fomichev <sdf@...ichev.me>
Cc: Andrii Nakryiko <andriin@...com>, Kernel Team <kernel-team@...com>,
Networking <netdev@...r.kernel.org>, bpf@...r.kernel.org,
Alexei Starovoitov <ast@...com>, Yonghong Song <yhs@...com>,
Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH v3 bpf] libbpf: detect supported kernel BTF features and
sanitize BTF
On Fri, May 10, 2019 at 2:36 PM Stanislav Fomichev <sdf@...ichev.me> wrote:
>
> 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?
It's not anymore. It's included from xsk.h, which is not internal, so
libbpf_util.h was recently exposed as public as well.
>
> > - 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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