x86,objtool: Separate unret validation from unwind hints

The ENTRY unwind hint type is serving double duty as both an empty
unwind hint and an unret validation annotation.

Unret validation is unrelated to unwinding. Separate it out into its own
annotation.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/ff7448d492ea21b86d8a90264b105fbd0d751077.1677683419.git.jpoimboe@kernel.org

2 files changed, 47 insertions, 22 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index efc2baa02883..10be80b3fe67 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2307,16 +2307,9 @@ static int read_unwind_hints(struct objtool_file *file)
 					WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
 						  insn->sec, insn->offset);
 				}
-
-				insn->entry = 1;
 			}
 		}
 
-		if (hint->type == UNWIND_HINT_TYPE_ENTRY) {
-			hint->type = UNWIND_HINT_TYPE_CALL;
-			insn->entry = 1;
-		}
-
 		if (hint->type == UNWIND_HINT_TYPE_FUNC) {
 			insn->cfi = &func_cfi;
 			continue;
@@ -2449,6 +2442,34 @@ static int read_instr_hints(struct objtool_file *file)
 	return 0;
 }
 
+static int read_validate_unret_hints(struct objtool_file *file)
+{
+	struct section *sec;
+	struct instruction *insn;
+	struct reloc *reloc;
+
+	sec = find_section_by_name(file->elf, ".rela.discard.validate_unret");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(reloc, &sec->reloc_list, list) {
+		if (reloc->sym->type != STT_SECTION) {
+			WARN("unexpected relocation symbol type in %s", sec->name);
+			return -1;
+		}
+
+		insn = find_insn(file, reloc->sym->sec, reloc->addend);
+		if (!insn) {
+			WARN("bad .discard.instr_end entry");
+			return -1;
+		}
+		insn->unret = 1;
+	}
+
+	return 0;
+}
+
+
 static int read_intra_function_calls(struct objtool_file *file)
 {
 	struct instruction *insn;
@@ -2667,6 +2688,10 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
+	ret = read_validate_unret_hints(file);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 
@@ -3863,10 +3888,10 @@ static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
 /*
  * Validate rethunk entry constraint: must untrain RET before the first RET.
  *
- * Follow every branch (intra-function) and ensure ANNOTATE_UNRET_END comes
+ * Follow every branch (intra-function) and ensure VALIDATE_UNRET_END comes
  * before an actual RET instruction.
  */
-static int validate_entry(struct objtool_file *file, struct instruction *insn)
+static int validate_unret(struct objtool_file *file, struct instruction *insn)
 {
 	struct instruction *next, *dest;
 	int ret, warnings = 0;
@@ -3874,10 +3899,10 @@ static int validate_entry(struct objtool_file *file, struct instruction *insn)
 	for (;;) {
 		next = next_insn_to_validate(file, insn);
 
-		if (insn->visited & VISITED_ENTRY)
+		if (insn->visited & VISITED_UNRET)
 			return 0;
 
-		insn->visited |= VISITED_ENTRY;
+		insn->visited |= VISITED_UNRET;
 
 		if (!insn->ignore_alts && insn->alts) {
 			struct alternative *alt;
@@ -3887,7 +3912,7 @@ static int validate_entry(struct objtool_file *file, struct instruction *insn)
 				if (alt->skip_orig)
 					skip_orig = true;
 
-				ret = validate_entry(file, alt->insn);
+				ret = validate_unret(file, alt->insn);
 				if (ret) {
 				        if (opts.backtrace)
 						BT_FUNC("(alt)", insn);
@@ -3915,7 +3940,7 @@ static int validate_entry(struct objtool_file *file, struct instruction *insn)
 						  insn->sec, insn->offset);
 					return -1;
 				}
-				ret = validate_entry(file, insn->jump_dest);
+				ret = validate_unret(file, insn->jump_dest);
 				if (ret) {
 					if (opts.backtrace) {
 						BT_FUNC("(branch%s)", insn,
@@ -3940,7 +3965,7 @@ static int validate_entry(struct objtool_file *file, struct instruction *insn)
 				return -1;
 			}
 
-			ret = validate_entry(file, dest);
+			ret = validate_unret(file, dest);
 			if (ret) {
 				if (opts.backtrace)
 					BT_FUNC("(call)", insn);
@@ -3976,19 +4001,19 @@ static int validate_entry(struct objtool_file *file, struct instruction *insn)
 }
 
 /*
- * Validate that all branches starting at 'insn->entry' encounter UNRET_END
- * before RET.
+ * Validate that all branches starting at VALIDATE_UNRET_BEGIN encounter
+ * VALIDATE_UNRET_END before RET.
  */
-static int validate_unret(struct objtool_file *file)
+static int validate_unrets(struct objtool_file *file)
 {
 	struct instruction *insn;
 	int ret, warnings = 0;
 
 	for_each_insn(file, insn) {
-		if (!insn->entry)
+		if (!insn->unret)
 			continue;
 
-		ret = validate_entry(file, insn);
+		ret = validate_unret(file, insn);
 		if (ret < 0) {
 			WARN_FUNC("Failed UNRET validation", insn->sec, insn->offset);
 			return ret;
@@ -4607,7 +4632,7 @@ int check(struct objtool_file *file)
 		 * Must be after validate_branch() and friends, it plays
 		 * further games with insn->visited.
 		 */
-		ret = validate_unret(file);
+		ret = validate_unrets(file);
 		if (ret < 0)
 			return ret;
 		warnings += ret;
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index 3e7c7004f7df..daa46f1f0965 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -61,7 +61,7 @@ struct instruction {
 	    restore		: 1,
 	    retpoline_safe	: 1,
 	    noendbr		: 1,
-	    entry		: 1,
+	    unret		: 1,
 	    visited		: 4,
 	    no_reloc		: 1;
 		/* 10 bit hole */
@@ -92,7 +92,7 @@ static inline struct symbol *insn_func(struct instruction *insn)
 #define VISITED_BRANCH		0x01
 #define VISITED_BRANCH_UACCESS	0x02
 #define VISITED_BRANCH_MASK	0x03
-#define VISITED_ENTRY		0x04
+#define VISITED_UNRET		0x04
 
 static inline bool is_static_jump(struct instruction *insn)
 {