linux-kernel - Re: [PATCH 18/20] objtool: Add UACCESS validation

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Date:   Sun, 10 Mar 2019 14:10:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, luto@...nel.org,
        bp@...en8.de, dvlasenk@...hat.com, linux-kernel@...r.kernel.org,
        dvyukov@...gle.com, rostedt@...dmis.org
Subject: Re: [PATCH 18/20] objtool: Add UACCESS validation

On Fri, Mar 08, 2019 at 03:02:09PM -0600, Josh Poimboeuf wrote:

> These gotos make my head spin.  Again I would much prefer a small amount
> of code duplication over this.

something like so then?

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1888,6 +1888,23 @@ static inline const char *insn_dest_name
 	return "{dynamic}";
 }
 
+static int validate_call(struct instruction *insn, struct insn_state *state)
+{
+	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
+		WARN_FUNC("call to %s() with UACCESS enabled",
+				insn->sec, insn->offset, insn_dest_name(insn));
+		return 1;
+	}
+
+	if (state->df) {
+		WARN_FUNC("call to %s() with DF set",
+				insn->sec, insn->offset, insn_dest_name(insn));
+		return 1;
+	}
+
+	return 0;
+}
+
 /*
  * Follow the branch starting at the given instruction, and recursively follow
  * any other branches (jumps).  Meanwhile, track the frame pointer state at
@@ -2036,25 +2053,9 @@ static int validate_branch(struct objtoo
 
 		case INSN_CALL:
 		case INSN_CALL_DYNAMIC:
-do_call:
-			if (state.uaccess && !func_uaccess_safe(insn->call_dest)) {
-				WARN_FUNC("call to %s() with UACCESS enabled",
-					  sec, insn->offset, insn_dest_name(insn));
-				return 1;
-			}
-
-			if (state.df) {
-				WARN_FUNC("call to %s() with DF set",
-					  sec, insn->offset, insn_dest_name(insn));
-				return 1;
-			}
-
-			if (insn->type == INSN_JUMP_UNCONDITIONAL ||
-			    insn->type == INSN_JUMP_DYNAMIC)
-				return 0;
-
-			if (insn->type == INSN_JUMP_CONDITIONAL)
-				break;
+			ret = validate_call(insn, &state);
+			if (ret)
+				return ret;
 
 			if (insn->type == INSN_CALL) {
 				if (is_fentry_call(insn))
@@ -2077,13 +2078,15 @@ static int validate_branch(struct objtoo
 		case INSN_JUMP_CONDITIONAL:
 		case INSN_JUMP_UNCONDITIONAL:
 			if (func && !insn->jump_dest) {
-do_sibling_call:
+				/* sibling call */
 				if (has_modified_stack_frame(&state)) {
 					WARN_FUNC("sibling call from callable instruction with modified stack frame",
 							sec, insn->offset);
 					return 1;
 				}
-				goto do_call;
+				ret = validate_call(insn, &state);
+				if (ret)
+					return ret;
 
 			} else if (insn->jump_dest &&
 				   (!func || !insn->jump_dest->func ||
@@ -2104,8 +2107,17 @@ static int validate_branch(struct objtoo
 			break;
 
 		case INSN_JUMP_DYNAMIC:
-			if (func && list_empty(&insn->alts))
-				goto do_sibling_call;
+			if (func && list_empty(&insn->alts)) {
+				/* sibling call */
+				if (has_modified_stack_frame(&state)) {
+					WARN_FUNC("sibling call from callable instruction with modified stack frame",
+							sec, insn->offset);
+					return 1;
+				}
+				ret = validate_call(insn, &state);
+				if (ret)
+					return ret;
+			}
 
 			return 0;