linux-kernel - [PATCH 5.10 038/148] objtool: Only rewrite unconditional retpoline thunk calls

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Message-Id: <20220723095235.007621512@linuxfoundation.org>
Date:   Sat, 23 Jul 2022 11:54:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lukasz Majczak <lma@...ihalf.com>,
        Nathan Chancellor <nathan@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ben Hutchings <ben@...adent.org.uk>
Subject: [PATCH 5.10 038/148] objtool: Only rewrite unconditional retpoline thunk calls

From: Peter Zijlstra <peterz@...radead.org>

commit 2d49b721dc18c113d5221f4cf5a6104eb66cb7f2 upstream.

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>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/objtool/arch/x86/decode.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -674,6 +674,10 @@ int arch_rewrite_retpolines(struct objto
 
 	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;