From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Wed, 17 Jul 2019 20:36:57 -0500
Subject: objtool: Support conditional retpolines
Git-commit: b68b9907069a8d3a65bc16a35360bf8f8603c8fa
Patch-mainline: v5.3-rc1
References: bsc#1202396

A Clang-built kernel is showing the following warning:

  arch/x86/kernel/platform-quirks.o: warning: objtool: x86_early_init_platform_quirks()+0x84: unreachable instruction

That corresponds to this code:

  7e:   0f 85 00 00 00 00       jne    84 <x86_early_init_platform_quirks+0x84>
                        80: R_X86_64_PC32       __x86_indirect_thunk_r11-0x4
  84:   c3                      retq

This is a conditional retpoline sibling call, which is now possible
thanks to retpolines.  Objtool hasn't seen that before.  It's
incorrectly interpreting the conditional jump as an unconditional
dynamic jump.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
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/30d4c758b267ef487fb97e6ecb2f148ad007b554.1563413318.git.jpoimboe@redhat.com

Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 tools/objtool/arch.h  |    1 +
 tools/objtool/check.c |   12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -27,6 +27,7 @@ enum insn_type {
 	INSN_JUMP_CONDITIONAL,
 	INSN_JUMP_UNCONDITIONAL,
 	INSN_JUMP_DYNAMIC,
+	INSN_JUMP_DYNAMIC_CONDITIONAL,
 	INSN_CALL,
 	INSN_CALL_DYNAMIC,
 	INSN_RETURN,
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -514,7 +514,11 @@ static int add_jump_destinations(struct
 			 * Retpoline jumps are really dynamic jumps in
 			 * disguise, so convert them accordingly.
 			 */
-			insn->type = INSN_JUMP_DYNAMIC;
+			if (insn->type == INSN_JUMP_UNCONDITIONAL)
+				insn->type = INSN_JUMP_DYNAMIC;
+			else
+				insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
+
 			insn->retpoline_safe = true;
 			continue;
 		} else {
@@ -1945,13 +1949,17 @@ static int validate_branch(struct objtoo
 			break;
 
 		case INSN_JUMP_DYNAMIC:
+		case INSN_JUMP_DYNAMIC_CONDITIONAL:
 			if (func && list_empty(&insn->alts)) {
 				ret = validate_sibling_call(insn, &state);
 				if (ret)
 					return ret;
 			}
 
-			return 0;
+			if (insn->type == INSN_JUMP_DYNAMIC)
+				return 0;
+
+			break;
 
 		case INSN_CONTEXT_SWITCH:
 			if (func && (!next_insn || !next_insn->hint)) {