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libbpf: Extend sanity checking ELF symbols with externs validation

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Add logic to validate extern symbols, plus some other minor extra checks, like
ELF symbol #0 validation, general symbol visibility and binding validations.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-10-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2021-04-23 11:13:39 -07:00
committed by Alexei Starovoitov
parent 42869d2852
commit 386b1d241e
1 changed files with 40 additions and 9 deletions
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49
tools/lib/bpf/linker.c
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@@ -750,14 +750,45 @@ static int linker_sanity_check_elf_symtab(struct src_obj *obj, struct src_sec *s
n = sec->shdr->sh_size / sec->shdr->sh_entsize; n = sec->shdr->sh_size / sec->shdr->sh_entsize;
sym = sec->data->d_buf; sym = sec->data->d_buf;
for (i = 0; i < n; i++, sym++) { for (i = 0; i < n; i++, sym++) {
if (sym->st_shndx int sym_type = ELF64_ST_TYPE(sym->st_info);
&& sym->st_shndx < SHN_LORESERVE int sym_bind = ELF64_ST_BIND(sym->st_info);
&& sym->st_shndx >= obj->sec_cnt) { int sym_vis = ELF64_ST_VISIBILITY(sym->st_other);
if (i == 0) {
if (sym->st_name != 0 || sym->st_info != 0
|| sym->st_other != 0 || sym->st_shndx != 0
|| sym->st_value != 0 || sym->st_size != 0) {
pr_warn("ELF sym #0 is invalid in %s\n", obj->filename);
return -EINVAL;
}
continue;
}
if (sym_bind != STB_LOCAL && sym_bind != STB_GLOBAL && sym_bind != STB_WEAK) {
pr_warn("ELF sym #%d in section #%zu has unsupported symbol binding %d\n",
i, sec->sec_idx, sym_bind);
return -EINVAL;
}
if (sym_vis != STV_DEFAULT && sym_vis != STV_HIDDEN) {
pr_warn("ELF sym #%d in section #%zu has unsupported symbol visibility %d\n",
i, sec->sec_idx, sym_vis);
return -EINVAL;
}
if (sym->st_shndx == 0) {
if (sym_type != STT_NOTYPE || sym_bind == STB_LOCAL
|| sym->st_value != 0 || sym->st_size != 0) {
pr_warn("ELF sym #%d is invalid extern symbol in %s\n",
i, obj->filename);
return -EINVAL;
}
continue;
}
if (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", 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); i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
return -EINVAL; return -EINVAL;
} }
if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) { if (sym_type == STT_SECTION) {
if (sym->st_value != 0) if (sym->st_value != 0)
return -EINVAL; return -EINVAL;
continue; continue;
@@ -1135,16 +1166,16 @@ static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj
size_t dst_sym_idx; size_t dst_sym_idx;
int name_off; int name_off;
/* we already have all-zero initial symbol */ /* We already validated all-zero symbol #0 and we already
if (sym->st_name == 0 && sym->st_info == 0 && * appended it preventively to the final SYMTAB, so skip it.
sym->st_other == 0 && sym->st_shndx == SHN_UNDEF && */
sym->st_value == 0 && sym->st_size ==0) if (i == 0)
continue; continue;
sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name); sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
if (!sym_name) { if (!sym_name) {
pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename); pr_warn("can't fetch symbol name for symbol #%d in '%s'\n", i, obj->filename);
return -1; return -EINVAL;
} }
if (sym->st_shndx && sym->st_shndx < SHN_LORESERVE) { if (sym->st_shndx && sym->st_shndx < SHN_LORESERVE) {