linux-kernel - [PATCH v2 04/20] objtool: Support retpoline jump detection for vmlinux.o

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Date:   Thu, 21 Jan 2021 15:29:20 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, Miroslav Benes <mbenes@...e.cz>
Subject: [PATCH v2 04/20] objtool: Support retpoline jump detection for vmlinux.o

Objtool converts direct retpoline jumps to type INSN_JUMP_DYNAMIC, since
that's what they are semantically.

That conversion doesn't work in vmlinux.o validation because the
indirect thunk function is present in the object, so the intra-object
jump check succeeds before the retpoline jump check gets a chance.

Rearrange the checks: check for a retpoline jump before checking for an
intra-object jump.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/check.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index c964cd56b557..5f5949951ca7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -781,10 +781,6 @@ static int add_jump_destinations(struct objtool_file *file)
 		} else if (reloc->sym->type == STT_SECTION) {
 			dest_sec = reloc->sym->sec;
 			dest_off = arch_dest_reloc_offset(reloc->addend);
-		} else if (reloc->sym->sec->idx) {
-			dest_sec = reloc->sym->sec;
-			dest_off = reloc->sym->sym.st_value +
-				   arch_dest_reloc_offset(reloc->addend);
 		} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21) ||
 			   !strncmp(reloc->sym->name, "__x86_retpoline_", 16)) {
 			/*
@@ -798,6 +794,10 @@ static int add_jump_destinations(struct objtool_file *file)
 
 			insn->retpoline_safe = true;
 			continue;
+		} else if (reloc->sym->sec->idx) {
+			dest_sec = reloc->sym->sec;
+			dest_off = reloc->sym->sym.st_value +
+				   arch_dest_reloc_offset(reloc->addend);
 		} else {
 			/* external sibling call */
 			insn->call_dest = reloc->sym;
-- 
2.29.2