linux-kernel - [PATCH v2 02/20] objtool: Fix retpoline detection in asm code

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Date:   Thu, 21 Jan 2021 15:29:18 -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 02/20] objtool: Fix retpoline detection in asm code

The JMP_NOSPEC macro branches to __x86_retpoline_*() rather than the
__x86_indirect_thunk_*() wrappers used by C code.  Detect jumps to
__x86_retpoline_*() as retpoline dynamic jumps.

Presumably this doesn't trigger a user-visible bug.  I only found it
when testing vmlinux.o validation.

Fixes: 39b735332cb8 ("objtool: Detect jumps to retpoline thunks")
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/arch/x86/special.c      |  2 +-
 tools/objtool/check.c                 |  3 ++-
 tools/objtool/include/objtool/check.h | 11 +++++++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
index b4bd3505fc94..e707d9bcd161 100644
--- a/tools/objtool/arch/x86/special.c
+++ b/tools/objtool/arch/x86/special.c
@@ -48,7 +48,7 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
 	 * replacement group.
 	 */
 	return insn->offset == special_alt->new_off &&
-	       (insn->type == INSN_CALL || is_static_jump(insn));
+	       (insn->type == INSN_CALL || is_jump(insn));
 }
 
 /*
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3bdd946c2027..081572170f6b 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -785,7 +785,8 @@ static int add_jump_destinations(struct objtool_file *file)
 			dest_sec = reloc->sym->sec;
 			dest_off = reloc->sym->sym.st_value +
 				   arch_dest_reloc_offset(reloc->addend);
-		} else if (strstr(reloc->sym->name, "_indirect_thunk_")) {
+		} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21) ||
+			   !strncmp(reloc->sym->name, "__x86_retpoline_", 16)) {
 			/*
 			 * Retpoline jumps are really dynamic jumps in
 			 * disguise, so convert them accordingly.
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index f4e041fbdab2..b408636c0201 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -68,6 +68,17 @@ static inline bool is_static_jump(struct instruction *insn)
 	       insn->type == INSN_JUMP_UNCONDITIONAL;
 }
 
+static inline bool is_dynamic_jump(struct instruction *insn)
+{
+	return insn->type == INSN_JUMP_DYNAMIC ||
+	       insn->type == INSN_JUMP_DYNAMIC_CONDITIONAL;
+}
+
+static inline bool is_jump(struct instruction *insn)
+{
+	return is_static_jump(insn) || is_dynamic_jump(insn);
+}
+
 struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);
 
-- 
2.29.2