objtool: use gelf_getsymshndx to handle >64k sections

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@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200421220843.188260-2-samitolvanen@google.com

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index b6349ca..8422567 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -343,12 +343,14 @@ 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) {
@@ -356,6 +358,10 @@ 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++) {
@@ -369,8 +375,9 @@ 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;
                }
 
@@ -384,10 +391,13 @@ 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);