linux-hardening - [PATCH 01/15] objtool: Find a destination for jumps beyond the section end

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Date:   Fri, 16 Apr 2021 13:38:30 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     x86@...nel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 01/15] objtool: Find a destination for jumps beyond the
 section end

With -ffunction-sections, Clang can generate a jump beyond the end of
a section when the section ends in an unreachable instruction. If the
offset matches the section length, use the last instruction as the
jump destination.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 tools/objtool/check.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index a0a8ce61cd4d..5fd60e055a5c 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -870,6 +870,10 @@ static int add_jump_destinations(struct objtool_file *file)
 		}
 
 		insn->jump_dest = find_insn(file, dest_sec, dest_off);
+
+		if (!insn->jump_dest && dest_sec->len == dest_off)
+			insn->jump_dest = find_last_insn(file, dest_sec);
+
 		if (!insn->jump_dest) {
 
 			/*
-- 
2.31.1.368.gbe11c130af-goog