objtool: Keep track of retpoline call sites

Provide infrastructure for architectures to rewrite/augment compiler
generated retpoline calls. Similar to what we do for static_call()s,
keep track of the instructions that are retpoline calls.

Use the same list_head, since a retpoline call cannot also be a
static_call.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151300.130805730@infradead.org

tools/objtool/check.c

@@ -451,7 +451,7 @@ static int create_static_call_sections(struct objtool_file *file)
 		return 0;
 
 	idx = 0;
-	list_for_each_entry(insn, &file->static_call_list, static_call_node)
+	list_for_each_entry(insn, &file->static_call_list, call_node)
 		idx++;
 
 	sec = elf_create_section(file->elf, ".static_call_sites", SHF_WRITE,
@@ -460,7 +460,7 @@ static int create_static_call_sections(struct objtool_file *file)
 		return -1;
 
 	idx = 0;
-	list_for_each_entry(insn, &file->static_call_list, static_call_node) {
+	list_for_each_entry(insn, &file->static_call_list, call_node) {
 
 		site = (struct static_call_site *)sec->data->d_buf + idx;
 		memset(site, 0, sizeof(struct static_call_site));
@@ -829,13 +829,16 @@ static int add_jump_destinations(struct objtool_file *file)
 			else
 				insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 
+			list_add_tail(&insn->call_node,
+				      &file->retpoline_call_list);
+
 			insn->retpoline_safe = true;
 			continue;
 		} else if (insn->func) {
 			/* internal or external sibling call (with reloc) */
 			insn->call_dest = reloc->sym;
 			if (insn->call_dest->static_call_tramp) {
-				list_add_tail(&insn->static_call_node,
+				list_add_tail(&insn->call_node,
 					      &file->static_call_list);
 			}
 			continue;
@@ -897,7 +900,7 @@ static int add_jump_destinations(struct objtool_file *file)
 				/* internal sibling call (without reloc) */
 				insn->call_dest = insn->jump_dest->func;
 				if (insn->call_dest->static_call_tramp) {
-					list_add_tail(&insn->static_call_node,
+					list_add_tail(&insn->call_node,
 						      &file->static_call_list);
 				}
 			}
@@ -981,6 +984,9 @@ static int add_call_destinations(struct objtool_file *file)
 			insn->type = INSN_CALL_DYNAMIC;
 			insn->retpoline_safe = true;
 
+			list_add_tail(&insn->call_node,
+				      &file->retpoline_call_list);
+
 			remove_insn_ops(insn);
 			continue;
 
@@ -988,7 +994,7 @@ static int add_call_destinations(struct objtool_file *file)
 			insn->call_dest = reloc->sym;
 
 		if (insn->call_dest && insn->call_dest->static_call_tramp) {
-			list_add_tail(&insn->static_call_node,
+			list_add_tail(&insn->call_node,
 				      &file->static_call_list);
 		}
 
@@ -1714,6 +1720,11 @@ static void mark_rodata(struct objtool_file *file)
 	file->rodata = found;
 }
 
+__weak int arch_rewrite_retpolines(struct objtool_file *file)
+{
+	return 0;
+}
+
 static int decode_sections(struct objtool_file *file)
 {
 	int ret;
@@ -1742,6 +1753,10 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
+	/*
+	 * Must be before add_special_section_alts() as that depends on
+	 * jump_dest being set.
+	 */
 	ret = add_jump_destinations(file);
 	if (ret)
 		return ret;
@@ -1778,6 +1793,15 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
+	/*
+	 * Must be after add_special_section_alts(), since this will emit
+	 * alternatives. Must be after add_{jump,call}_destination(), since
+	 * those create the call insn lists.
+	 */
+	ret = arch_rewrite_retpolines(file);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 

tools/objtool/include/objtool/arch.h

@@ -88,4 +88,6 @@ int arch_decode_hint_reg(struct instruction *insn, u8 sp_reg);
 
 bool arch_is_retpoline(struct symbol *sym);
 
+int arch_rewrite_retpolines(struct objtool_file *file);
+
 #endif /* _ARCH_H */

tools/objtool/include/objtool/check.h

@@ -39,7 +39,7 @@ struct alt_group {
 struct instruction {
 	struct list_head list;
 	struct hlist_node hash;
-	struct list_head static_call_node;
+	struct list_head call_node;
 	struct list_head mcount_loc_node;
 	struct section *sec;
 	unsigned long offset;

tools/objtool/include/objtool/objtool.h

@@ -18,6 +18,7 @@ struct objtool_file {
 	struct elf *elf;
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 20);
+	struct list_head retpoline_call_list;
 	struct list_head static_call_list;
 	struct list_head mcount_loc_list;
 	bool ignore_unreachables, c_file, hints, rodata;

tools/objtool/objtool.c

@@ -61,6 +61,7 @@ struct objtool_file *objtool_open_read(const char *_objname)
 
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
+	INIT_LIST_HEAD(&file.retpoline_call_list);
 	INIT_LIST_HEAD(&file.static_call_list);
 	INIT_LIST_HEAD(&file.mcount_loc_list);
 	file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");