Merge tag 'objtool-urgent-2021-06-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool fixes from Ingo Molnar:
 "Two objtool fixes:

   - fix a bug that corrupts the code by mistakenly rewriting
     conditional jumps

   - fix another bug generating an incorrect ELF symbol table
     during retpoline rewriting"

* tag 'objtool-urgent-2021-06-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  objtool: Only rewrite unconditional retpoline thunk calls
  objtool: Fix .symtab_shndx handling for elf_create_undef_symbol()

Author: torvalds

tools/objtool/arch/x86/decode.c

@@ -747,6 +747,10 @@ int arch_rewrite_retpolines(struct objtool_file *file)
 
 	list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
 
+		if (insn->type != INSN_JUMP_DYNAMIC &&
+		    insn->type != INSN_CALL_DYNAMIC)
+			continue;
+
 		if (!strcmp(insn->sec->name, ".text.__x86.indirect_thunk"))
 			continue;
 

tools/objtool/elf.c

@@ -717,7 +717,7 @@ static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
 
 struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
 {
-	struct section *symtab;
+	struct section *symtab, *symtab_shndx;
 	struct symbol *sym;
 	Elf_Data *data;
 	Elf_Scn *s;
@@ -769,6 +769,29 @@ struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
 	symtab->len += data->d_size;
 	symtab->changed = true;
 
+	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+	if (symtab_shndx) {
+		s = elf_getscn(elf->elf, symtab_shndx->idx);
+		if (!s) {
+			WARN_ELF("elf_getscn");
+			return NULL;
+		}
+
+		data = elf_newdata(s);
+		if (!data) {
+			WARN_ELF("elf_newdata");
+			return NULL;
+		}
+
+		data->d_buf = &sym->sym.st_size; /* conveniently 0 */
+		data->d_size = sizeof(Elf32_Word);
+		data->d_align = 4;
+		data->d_type = ELF_T_WORD;
+
+		symtab_shndx->len += 4;
+		symtab_shndx->changed = true;
+	}
+
 	sym->sec = find_section_by_index(elf, 0);
 
 	elf_add_symbol(elf, sym);