From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Wed, 17 Jul 2019 20:36:47 -0500
Subject: objtool: Track original function across branches
Git-commit: c705cecc8431951b4f34178e6b1db51b4a504c43
Patch-mainline: v5.3-rc1
References: bsc#1202396

If 'insn->func' is NULL, objtool skips some important checks, including
sibling call validation.  So if some .fixup code does an invalid sibling
call, objtool ignores it.

Treat all code branches (including alts) as part of the original
function by keeping track of the original func value from
validate_functions().

This improves the usefulness of some clang function fallthrough
warnings, and exposes some additional kernel bugs in the process.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/505df630f33c9717e1ccde6e4b64c5303135c25f.1563413318.git.jpoimboe@redhat.com

Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 tools/objtool/check.c |   24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1788,13 +1788,12 @@ static int validate_sibling_call(struct
  * each instruction and validate all the rules described in
  * tools/objtool/Documentation/stack-validation.txt.
  */
-static int validate_branch(struct objtool_file *file, struct instruction *first,
-			   struct insn_state state)
+static int validate_branch(struct objtool_file *file, struct symbol *func,
+			   struct instruction *first, struct insn_state state)
 {
 	struct alternative *alt;
 	struct instruction *insn, *next_insn;
 	struct section *sec;
-	struct symbol *func = NULL;
 	int ret;
 
 	insn = first;
@@ -1815,9 +1814,6 @@ static int validate_branch(struct objtoo
 			return 1;
 		}
 
-		if (insn->func)
-			func = insn->func->pfunc;
-
 		if (func && insn->ignore) {
 			WARN_FUNC("BUG: why am I validating an ignored function?",
 				  sec, insn->offset);
@@ -1837,7 +1833,7 @@ static int validate_branch(struct objtoo
 
 				i = insn;
 				save_insn = NULL;
-				func_for_each_insn_continue_reverse(file, insn->func, i) {
+				func_for_each_insn_continue_reverse(file, func, i) {
 					if (i->save) {
 						save_insn = i;
 						break;
@@ -1883,7 +1879,7 @@ static int validate_branch(struct objtoo
 				if (alt->skip_orig)
 					skip_orig = true;
 
-				ret = validate_branch(file, alt->insn, state);
+				ret = validate_branch(file, func, alt->insn, state);
 				if (ret) {
 					if (backtrace)
 						BT_FUNC("(alt)", insn);
@@ -1906,7 +1902,7 @@ static int validate_branch(struct objtoo
 
 			if (state.bp_scratch) {
 				WARN("%s uses BP as a scratch register",
-				     insn->func->name);
+				     func->name);
 				return 1;
 			}
 
@@ -1941,8 +1937,8 @@ static int validate_branch(struct objtoo
 			} else if (insn->jump_dest &&
 				   (!func || !insn->jump_dest->func ||
 				    insn->jump_dest->func->pfunc == func)) {
-				ret = validate_branch(file, insn->jump_dest,
-						      state);
+				ret = validate_branch(file, func,
+						      insn->jump_dest, state);
 				if (ret) {
 					if (backtrace)
 						BT_FUNC("(branch)", insn);
@@ -2011,7 +2007,7 @@ static int validate_unwind_hints(struct
 
 	for_each_insn(file, insn) {
 		if (insn->hint && !insn->visited) {
-			ret = validate_branch(file, insn, state);
+			ret = validate_branch(file, insn->func, insn, state);
 			if (ret && backtrace)
 				BT_FUNC("<=== (hint)", insn);
 			warnings += ret;
@@ -2138,10 +2134,10 @@ static int validate_functions(struct obj
 				continue;
 
 			insn = find_insn(file, sec, func->offset);
-			if (!insn || insn->ignore)
+			if (!insn || insn->ignore || insn->visited)
 				continue;
 
-			ret = validate_branch(file, insn, state);
+			ret = validate_branch(file, func, insn, state);
 			if (ret && backtrace)
 				BT_FUNC("<=== (func)", insn);
 			warnings += ret;