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mx.microsoft.com 1; spf=pass smtp.mailfrom=fb.com; dmarc=pass action=none header.from=fb.com; dkim=pass header.d=fb.com; arc=none Received: from SN6PR1501MB2064.namprd15.prod.outlook.com (2603:10b6:805:d::27) by SA0PR15MB3917.namprd15.prod.outlook.com (2603:10b6:806:87::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4065.21; Thu, 22 Apr 2021 16:06:18 +0000 Received: from SN6PR1501MB2064.namprd15.prod.outlook.com ([fe80::f433:fd99:f905:8912]) by SN6PR1501MB2064.namprd15.prod.outlook.com ([fe80::f433:fd99:f905:8912%3]) with mapi id 15.20.4065.021; Thu, 22 Apr 2021 16:06:18 +0000 Subject: Re: [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos sanity checks To: Andrii Nakryiko , , , , CC: References: <20210416202404.3443623-1-andrii@kernel.org> <20210416202404.3443623-8-andrii@kernel.org> From: Yonghong Song Message-ID: <6fb105a3-ffc3-1970-8833-429e5b624e31@fb.com> Date: Thu, 22 Apr 2021 09:06:15 -0700 User-Agent: Mozilla/5.0 (Macintosh; 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They are already quite extensive and are suffering from too > deep indentation. Subsequent changes will extend SYMTAB sanity checking > further, so it's better to factor each into a separate function. > > No functional changes are intended. > > Signed-off-by: Andrii Nakryiko Ack with a minor suggestion below. Acked-by: Yonghong Song > --- > tools/lib/bpf/linker.c | 233 ++++++++++++++++++++++------------------- > 1 file changed, 127 insertions(+), 106 deletions(-) > > diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c > index 4e08bc07e635..0bb927226370 100644 > --- a/tools/lib/bpf/linker.c > +++ b/tools/lib/bpf/linker.c > @@ -131,6 +131,8 @@ static int init_output_elf(struct bpf_linker *linker, const char *file); > > static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, struct src_obj *obj); > static int linker_sanity_check_elf(struct src_obj *obj); > +static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec); > +static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *sec); > static int linker_sanity_check_btf(struct src_obj *obj); > static int linker_sanity_check_btf_ext(struct src_obj *obj); > static int linker_fixup_btf(struct src_obj *obj); > @@ -663,8 +665,8 @@ static bool is_pow_of_2(size_t x) > > static int linker_sanity_check_elf(struct src_obj *obj) > { > - struct src_sec *sec, *link_sec; > - int i, j, n; > + struct src_sec *sec; > + int i, err; > > if (!obj->symtab_sec_idx) { > pr_warn("ELF is missing SYMTAB section in %s\n", obj->filename); > @@ -692,43 +694,11 @@ static int linker_sanity_check_elf(struct src_obj *obj) > return -EINVAL; > > switch (sec->shdr->sh_type) { > - case SHT_SYMTAB: { > - Elf64_Sym *sym; > - > - if (sec->shdr->sh_entsize != sizeof(Elf64_Sym)) > - return -EINVAL; > - if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0) > - return -EINVAL; > - > - if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) { > - pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n", > - sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename); > - return -EINVAL; > - } > - link_sec = &obj->secs[sec->shdr->sh_link]; > - if (link_sec->shdr->sh_type != SHT_STRTAB) { > - pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n", > - sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename); > - return -EINVAL; > - } > - > - n = sec->shdr->sh_size / sec->shdr->sh_entsize; > - sym = sec->data->d_buf; > - for (j = 0; j < n; j++, sym++) { > - if (sym->st_shndx > - && sym->st_shndx < SHN_LORESERVE > - && sym->st_shndx >= obj->sec_cnt) { > - pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n", > - j, sec->sec_idx, (size_t)sym->st_shndx, obj->filename); > - return -EINVAL; > - } > - if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) { > - if (sym->st_value != 0) > - return -EINVAL; > - } > - } > + case SHT_SYMTAB: > + err = linker_sanity_check_elf_symtab(obj, sec); > + if (err) > + return err; > break; > - } > case SHT_STRTAB: > break; > case SHT_PROGBITS: > @@ -739,87 +709,138 @@ static int linker_sanity_check_elf(struct src_obj *obj) > break; > case SHT_NOBITS: > break; > - case SHT_REL: { > - Elf64_Rel *relo; > - struct src_sec *sym_sec; > + case SHT_REL: > + err = linker_sanity_check_elf_relos(obj, sec); > + if (err) > + return err; > + break; > + case SHT_LLVM_ADDRSIG: > + break; > + default: > + pr_warn("ELF section #%zu (%s) has unrecognized type %zu in %s\n", > + sec->sec_idx, sec->sec_name, (size_t)sec->shdr->sh_type, obj->filename); > + return -EINVAL; > + } > + } > > - if (sec->shdr->sh_entsize != sizeof(Elf64_Rel)) > - return -EINVAL; > - if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0) > - return -EINVAL; > + return 0; > +} > > - /* SHT_REL's sh_link should point to SYMTAB */ > - if (sec->shdr->sh_link != obj->symtab_sec_idx) { > - pr_warn("ELF relo section #%zu points to invalid SYMTAB section #%zu in %s\n", > - sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename); > - return -EINVAL; > - } > +static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *sec) > +{ > + struct src_sec *link_sec; > + Elf64_Sym *sym; > + int i, n; > > - /* SHT_REL's sh_info points to relocated section */ > - if (!sec->shdr->sh_info || sec->shdr->sh_info >= obj->sec_cnt) { > - pr_warn("ELF relo section #%zu points to missing section #%zu in %s\n", > - sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename); > - return -EINVAL; > - } > - link_sec = &obj->secs[sec->shdr->sh_info]; > + if (sec->shdr->sh_entsize != sizeof(Elf64_Sym)) > + return -EINVAL; > + if (sec->shdr->sh_size % sec->shdr->sh_entsize != 0) > + return -EINVAL; > + > + if (!sec->shdr->sh_link || sec->shdr->sh_link >= obj->sec_cnt) { > + pr_warn("ELF SYMTAB section #%zu points to missing STRTAB section #%zu in %s\n", > + sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename); > + return -EINVAL; > + } > + link_sec = &obj->secs[sec->shdr->sh_link]; > + if (link_sec->shdr->sh_type != SHT_STRTAB) { > + pr_warn("ELF SYMTAB section #%zu points to invalid STRTAB section #%zu in %s\n", > + sec->sec_idx, (size_t)sec->shdr->sh_link, obj->filename); > + return -EINVAL; > + } > > - /* .rel -> pattern is followed */ > - if (strncmp(sec->sec_name, ".rel", sizeof(".rel") - 1) != 0 > - || strcmp(sec->sec_name + sizeof(".rel") - 1, link_sec->sec_name) != 0) { > - pr_warn("ELF relo section #%zu name has invalid name in %s\n", > - sec->sec_idx, obj->filename); > + n = sec->shdr->sh_size / sec->shdr->sh_entsize; > + sym = sec->data->d_buf; > + for (i = 0; i < n; i++, sym++) { > + if (sym->st_shndx > + && sym->st_shndx < SHN_LORESERVE > + && sym->st_shndx >= obj->sec_cnt) { > + pr_warn("ELF sym #%d in section #%zu points to missing section #%zu in %s\n", > + i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename); > + return -EINVAL; > + } > + if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) { > + if (sym->st_value != 0) > return -EINVAL; > - } > + continue; I think this "continue" is not necessary. > + } > + } > > - /* don't further validate relocations for ignored sections */ > - if (link_sec->skipped) > - break; > + return 0; > +} > > - /* relocatable section is data or instructions */ > - if (link_sec->shdr->sh_type != SHT_PROGBITS > - && link_sec->shdr->sh_type != SHT_NOBITS) { > - pr_warn("ELF relo section #%zu points to invalid section #%zu in %s\n", > - sec->sec_idx, (size_t)sec->shdr->sh_info, obj->filename); > - return -EINVAL; > - } [...]