linux-kernel - [tip: objtool/urgent] objtool: Only rewrite unconditional retpoline thunk calls

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Date:   Sat, 12 Jun 2021 06:42:47 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Lukasz Majczak <lma@...ihalf.com>,
        Nathan Chancellor <nathan@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: objtool/urgent] objtool: Only rewrite unconditional retpoline
 thunk calls

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     2d49b721dc18c113d5221f4cf5a6104eb66cb7f2
Gitweb:        https://git.kernel.org/tip/2d49b721dc18c113d5221f4cf5a6104eb66cb7f2
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 10 Jun 2021 09:04:29 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 11 Jun 2021 08:53:06 +02:00

objtool: Only rewrite unconditional retpoline thunk calls

It turns out that the compilers generate conditional branches to the
retpoline thunks like:

  5d5:   0f 85 00 00 00 00       jne    5db <cpuidle_reflect+0x22>
	5d7: R_X86_64_PLT32     __x86_indirect_thunk_r11-0x4

while the rewrite can only handle JMP/CALL to the thunks. The result
is the alternative wrecking the code. Make sure to skip writing the
alternatives for conditional branches.

Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls")
Reported-by: Lukasz Majczak <lma@...ihalf.com>
Reported-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Nathan Chancellor <nathan@...nel.org>
---
 tools/objtool/arch/x86/decode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 24295d3..523aa41 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -747,6 +747,10 @@ int arch_rewrite_retpolines(struct objtool_file *file)
 
 	list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
 
+		if (insn->type != INSN_JUMP_DYNAMIC &&
+		    insn->type != INSN_CALL_DYNAMIC)
+			continue;
+
 		if (!strcmp(insn->sec->name, ".text.__x86.indirect_thunk"))
 			continue;