[PATCH v2 1/2] objtool: use gelf_getsymshndx to handle >64k sections

From: Sami Tolvanen
Date: Tue Apr 21 2020 - 18:08:59 EST


Currently, objtool fails to load the correct section for symbols when
the index is greater than SHN_LORESERVE. Use gelf_getsymshndx instead
of gelf_getsym to handle >64k sections.

Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
tools/objtool/elf.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 09ddc8f1def3..887445e87380 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -327,12 +327,14 @@ static int read_sections(struct elf *elf)

static int read_symbols(struct elf *elf)
{
- struct section *symtab, *sec;
+ struct section *symtab, *symtab_shndx, *sec;
struct symbol *sym, *pfunc;
struct list_head *entry;
struct rb_node *pnode;
int symbols_nr, i;
char *coldstr;
+ Elf_Data *shndx_data = NULL;
+ Elf32_Word shndx;

symtab = find_section_by_name(elf, ".symtab");
if (!symtab) {
@@ -340,6 +342,10 @@ static int read_symbols(struct elf *elf)
return -1;
}

+ symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+ if (symtab_shndx)
+ shndx_data = symtab_shndx->data;
+
symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;

for (i = 0; i < symbols_nr; i++) {
@@ -353,8 +359,9 @@ static int read_symbols(struct elf *elf)

sym->idx = i;

- if (!gelf_getsym(symtab->data, i, &sym->sym)) {
- WARN_ELF("gelf_getsym");
+ if (!gelf_getsymshndx(symtab->data, shndx_data, i, &sym->sym,
+ &shndx)) {
+ WARN_ELF("gelf_getsymshndx");
goto err;
}

@@ -368,10 +375,13 @@ static int read_symbols(struct elf *elf)
sym->type = GELF_ST_TYPE(sym->sym.st_info);
sym->bind = GELF_ST_BIND(sym->sym.st_info);

- if (sym->sym.st_shndx > SHN_UNDEF &&
- sym->sym.st_shndx < SHN_LORESERVE) {
- sym->sec = find_section_by_index(elf,
- sym->sym.st_shndx);
+ if ((sym->sym.st_shndx > SHN_UNDEF &&
+ sym->sym.st_shndx < SHN_LORESERVE) ||
+ (shndx_data && sym->sym.st_shndx == SHN_XINDEX)) {
+ if (sym->sym.st_shndx != SHN_XINDEX)
+ shndx = sym->sym.st_shndx;
+
+ sym->sec = find_section_by_index(elf, shndx);
if (!sym->sec) {
WARN("couldn't find section for symbol %s",
sym->name);
--
2.26.1.301.g55bc3eb7cb9-goog