From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BBF5C04AB2 for ; Fri, 10 May 2019 09:46:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D687F20989 for ; Fri, 10 May 2019 09:46:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=cloudflare.com header.i=@cloudflare.com header.b="LBpEDVI7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727289AbfEJJqF (ORCPT ); Fri, 10 May 2019 05:46:05 -0400 Received: from mail-ot1-f67.google.com ([209.85.210.67]:43942 "EHLO mail-ot1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727280AbfEJJqF (ORCPT ); Fri, 10 May 2019 05:46:05 -0400 Received: by mail-ot1-f67.google.com with SMTP id i8so4992121oth.10 for ; Fri, 10 May 2019 02:46:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Sgf6/Y0UrQwr/GHU2maYyg/BfKDCw3g4VFByGLRwIiY=; b=LBpEDVI7whBRF2VOskAKkiKyZeBOjMwMz5aePVInr0jalUjLwgy8KSJ2oa12Dx2kKF 3w0rXa/2x67nOAizalC4Fy1jOQMS3tmZ6pqchAWWG4N6bWHsLSZfx6AIPl8dXp4a2M3H TwD+o8MAX6Sh/9JoSZS8N8DJhw+M7S1BE3Z+s= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Sgf6/Y0UrQwr/GHU2maYyg/BfKDCw3g4VFByGLRwIiY=; b=NUwcF6lisfDmsCoxejfTfe6lu4QeN7o2VrDI2/UmYSpLJrbDbqekkMiLLsw8+dgOue 9b99s+VedrFAelj5GzX/loKp2K8J28VMJ1jLCmRsplyzHiq04UPap0/ZHfK9cjsQtOKL AhpPN2cld4hEP991vD7cTwL+jSMt2dYyDuTneyyxmfNFE/4a2ktbPM2qfqzAexRfgRav nOMECwmxwnn7SN4QrCrMhHgKKVc++HFIagiRz/MYE9K0sU90kf5m571GbDdrZe5BBuGz kfqok6vX0IL2askjxKwmAeq3WR+S7TIJhyyZClHtVM5KMuUq3cWkIYsx87JFYhVnEwQg PJRA== X-Gm-Message-State: APjAAAVIi79n9/jV2MOjp2T1rQ0RFHeAqwvlOT6iznB7MGVTQEj1u/mr agHqQRgMB6+W971pZ0dI3MWruYs9TKcIljVuVx32/g== X-Google-Smtp-Source: APXvYqxS3BHgUGVkhumKxSed4443GmY/zHdlFcdt5tg0QXna6de51aUarqZoyxty23M5JpEO0iQUjn7381mzQFf0Le8= X-Received: by 2002:a9d:694a:: with SMTP id p10mr6289641oto.61.1557481564554; Fri, 10 May 2019 02:46:04 -0700 (PDT) MIME-Version: 1.0 References: <20190510043723.3359135-1-andriin@fb.com> In-Reply-To: <20190510043723.3359135-1-andriin@fb.com> From: Lorenz Bauer Date: Fri, 10 May 2019 10:45:53 +0100 Message-ID: Subject: Re: [PATCH bpf] libbpf: detect supported kernel BTF features and sanitize BTF To: Andrii Nakryiko Cc: andrii.nakryiko@gmail.com, netdev@vger.kernel.org, bpf@vger.kernel.org, Daniel Borkmann , Alexei Starovoitov , yhs@fb.com Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, 10 May 2019 at 05:37, 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. For sys_bpf, we ignore a zero tail in struct bpf_attr, which gives us backwards / forwards compatibility as long as the user doesn't use the new fields. Do we need a similar mechanism for BTF? Is it possible to discard unknown types at load time? > > 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. > > Reported-by: Alexei Starovoitov > Signed-off-by: Andrii Nakryiko > --- > tools/lib/bpf/libbpf.c | 185 ++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 184 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 11a65db4b93f..0813c4ad5d11 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -128,6 +128,10 @@ 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 +1025,81 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx) > return false; > } > > +static void bpf_object__sanitize_btf(struct bpf_object *obj) > +{ > +#define BTF_INFO_ENC(kind, kind_flag, vlen) \ > + ((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN)) > +#define BTF_INT_ENC(encoding, bits_offset, nr_bits) \ > + ((encoding) << 24 | (bits_offset) << 16 | (nr_bits)) > + > + 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); > + } > + } > +#undef BTF_INFO_ENC > +#undef BTF_INT_ENC > +} > + > +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 +1243,10 @@ 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 +1268,8 @@ 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 +1639,112 @@ bpf_object__probe_global_data(struct bpf_object *obj) > return 0; > } > > +static int try_load_btf(const char *raw_types, size_t types_len, > + const char *str_sec, size_t str_len) > +{ > + char buf[1024]; > + 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, buf, 1024, 0); > + if (btf_fd < 0) { > + free(raw_btf); > + return 0; > + } > + > + close(btf_fd); > + free(raw_btf); > + return 1; > +} > + > +#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_PARAM_ENC(name, type) (name), (type) > +#define BTF_VAR_SECINFO_ENC(type, offset, size) (type), (offset), (size) > +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 = try_load_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 = try_load_btf((char *)&types, sizeof(types), strs, sizeof(strs)); > + if (res < 0) > + return res; > + if (res > 0) > + obj->caps.btf_datasec = 1; > + return 0; > +} > +#undef BTF_INFO_ENC > +#undef BTF_TYPE_ENC > +#undef BTF_INT_ENC > +#undef BTF_TYPE_INT_ENC > +#undef BTF_PARAM_ENC > +#undef BTF_VAR_SECINFO_ENC > + > 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; > > -- > 2.17.1 > -- Lorenz Bauer | Systems Engineer 25 Lavington St., London SE1 0NZ www.cloudflare.com