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Date: Thu, 22 Apr 2021 09:06:15 -0700
From: Yonghong Song <yhs@...com>
To: Andrii Nakryiko <andrii@...nel.org>, <bpf@...r.kernel.org>,
<netdev@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>
CC: <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos
sanity checks
On 4/16/21 1:23 PM, Andrii Nakryiko wrote:
> Factor out logic for sanity checking SHT_SYMTAB and SHT_REL sections into
> separate sections. 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 <andrii@...nel.org>
Ack with a minor suggestion below.
Acked-by: Yonghong Song <yhs@...com>
> ---
> 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<secname> -> <secname> 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;
> - }
[...]
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