From: Josh Poimboeuf jpoimboe@redhat.com
[ Upstream commit bd841d6154f5f41f8a32d3c1b0bc229e326e640a ]
CONFIG_UBSAN_TRAP causes GCC to emit a UD2 whenever it encounters an unreachable code path. This includes __builtin_unreachable(). Because the BUG() macro uses __builtin_unreachable() after it emits its own UD2, this results in a double UD2. In this case objtool rightfully detects that the second UD2 is unreachable:
init/main.o: warning: objtool: repair_env_string()+0x1c8: unreachable instruction
We weren't able to figure out a way to get rid of the double UD2s, so just silence the warning.
Reported-by: Randy Dunlap rdunlap@infradead.org Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Borislav Petkov bp@suse.de Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Miroslav Benes mbenes@suse.cz Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/6653ad73c6b59c049211bd7c11ed3809c20ee9f5.158576102... Signed-off-by: Sasha Levin sashal@kernel.org --- tools/objtool/check.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 9479c74..4613d79 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2086,14 +2086,27 @@ static bool ignore_unreachable_insn(struct instruction *insn) !strcmp(insn->sec->name, ".altinstr_aux")) return true;
+ if (!insn->func) + return false; + + /* + * CONFIG_UBSAN_TRAP inserts a UD2 when it sees + * __builtin_unreachable(). The BUG() macro has an unreachable() after + * the UD2, which causes GCC's undefined trap logic to emit another UD2 + * (or occasionally a JMP to UD2). + */ + if (list_prev_entry(insn, list)->dead_end && + (insn->type == INSN_BUG || + (insn->type == INSN_JUMP_UNCONDITIONAL && + insn->jump_dest && insn->jump_dest->type == INSN_BUG))) + return true; + /* * Check if this (or a subsequent) instruction is related to * CONFIG_UBSAN or CONFIG_KASAN. * * End the search at 5 instructions to avoid going into the weeds. */ - if (!insn->func) - return false; for (i = 0; i < 5; i++) {
if (is_kasan_insn(insn) || is_ubsan_insn(insn))