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authorAndrii Nakryiko <andrii@kernel.org>2021-04-23 21:13:39 +0300
committerAlexei Starovoitov <ast@kernel.org>2021-04-24 00:05:26 +0300
commit386b1d241e1b975a239d33be836bc183a52ab18c (patch)
treec27ffb88789c8cdb3f0da7dbfcaeaecd7913e239
parent42869d28527695a75346c988ceeedbba7e3880b7 (diff)
downloadlinux-386b1d241e1b975a239d33be836bc183a52ab18c.tar.xz
libbpf: Extend sanity checking ELF symbols with externs validation
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
-rw-r--r--tools/lib/bpf/linker.c49
1 files changed, 40 insertions, 9 deletions
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 1263641e8b97..b0e038480300 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -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;
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) {
+ int sym_type = ELF64_ST_TYPE(sym->st_info);
+ int sym_bind = ELF64_ST_BIND(sym->st_info);
+ 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",
i, sec->sec_idx, (size_t)sym->st_shndx, obj->filename);
return -EINVAL;
}
- if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION) {
+ if (sym_type == STT_SECTION) {
if (sym->st_value != 0)
return -EINVAL;
continue;
@@ -1135,16 +1166,16 @@ static int linker_append_elf_syms(struct bpf_linker *linker, struct src_obj *obj
size_t dst_sym_idx;
int name_off;
- /* we already have all-zero initial symbol */
- if (sym->st_name == 0 && sym->st_info == 0 &&
- sym->st_other == 0 && sym->st_shndx == SHN_UNDEF &&
- sym->st_value == 0 && sym->st_size ==0)
+ /* We already validated all-zero symbol #0 and we already
+ * appended it preventively to the final SYMTAB, so skip it.
+ */
+ if (i == 0)
continue;
sym_name = elf_strptr(obj->elf, str_sec_idx, sym->st_name);
if (!sym_name) {
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) {