[PATCH 5.10 038/130] objtool: Only rewrite unconditional retpoline thunk calls

From: Greg Kroah-Hartman
Date: Tue Jul 12 2022 - 14:44:24 EST

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

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@xxxxxxxxxxxx>
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
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"))