objtool: Support conditional retpolines

A Clang-built kernel is showing the following warning:

  arch/x86/kernel/platform-quirks.o: warning: objtool: x86_early_init_platform_quirks()+0x84: unreachable instruction

That corresponds to this code:

  7e:   0f 85 00 00 00 00       jne    84 <x86_early_init_platform_quirks+0x84>
                        80: R_X86_64_PC32       __x86_indirect_thunk_r11-0x4
  84:   c3                      retq

This is a conditional retpoline sibling call, which is now possible
thanks to retpolines.  Objtool hasn't seen that before.  It's
incorrectly interpreting the conditional jump as an unconditional
dynamic jump.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/30d4c758b267ef487fb97e6ecb2f148ad007b554.1563413318.git.jpoimboe@redhat.com

diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index 50448c0c4bca14769d07f9595ce4e33a168654a2..ced3765c4f4445daf3d1d8db2851af6955978ca5 100644 (file)
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -15,6 +15,7 @@ enum insn_type {
        INSN_JUMP_CONDITIONAL,
        INSN_JUMP_UNCONDITIONAL,
        INSN_JUMP_DYNAMIC,
+       INSN_JUMP_DYNAMIC_CONDITIONAL,
        INSN_CALL,
        INSN_CALL_DYNAMIC,
        INSN_RETURN,

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 04572a049cfc3db52ff367e5ca152953ff569b7d..5f26620f13f56fdb2aec4668e0495a569f0bd049 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -575,7 +575,11 @@ static int add_jump_destinations(struct objtool_file *file)
                         * Retpoline jumps are really dynamic jumps in
                         * disguise, so convert them accordingly.
                         */
-                       insn->type = INSN_JUMP_DYNAMIC;
+                       if (insn->type == INSN_JUMP_UNCONDITIONAL)
+                               insn->type = INSN_JUMP_DYNAMIC;
+                       else
+                               insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
+
                        insn->retpoline_safe = true;
                        continue;
                } else {
@@ -2114,13 +2118,17 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
                        break;
 
                case INSN_JUMP_DYNAMIC:
+               case INSN_JUMP_DYNAMIC_CONDITIONAL:
                        if (func && is_sibling_call(insn)) {
                                ret = validate_sibling_call(insn, &state);
                                if (ret)
                                        return ret;
                        }
 
-                       return 0;
+                       if (insn->type == INSN_JUMP_DYNAMIC)
+                               return 0;
+
+                       break;
 
                case INSN_CONTEXT_SWITCH:
                        if (func && (!next_insn || !next_insn->hint)) {