Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933397AbeAKVrC (ORCPT + 1 other); Thu, 11 Jan 2018 16:47:02 -0500 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:5360 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932472AbeAKVq4 (ORCPT ); Thu, 11 Jan 2018 16:46:56 -0500 X-IronPort-AV: E=Sophos;i="5.46,346,1511827200"; d="scan'208";a="585776758" From: David Woodhouse To: Andi Kleen Cc: Paul Turner , LKML , Linus Torvalds , Greg Kroah-Hartman , Tim Chen , Dave Hansen , tglx@linutronix.de, Kees Cook , Rik van Riel , Peter Zijlstra , Andy Lutomirski , Jiri Kosina , gnomes@lxorguk.ukuu.org.uk, x86@kernel.org, thomas.lendacky@amd.com, Josh Poimboeuf Subject: [PATCH v8 02/12] objtool: Allow alternatives to be ignored Date: Thu, 11 Jan 2018 21:46:24 +0000 Message-Id: <1515707194-20531-3-git-send-email-dwmw@amazon.co.uk> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1515707194-20531-1-git-send-email-dwmw@amazon.co.uk> References: <1515707194-20531-1-git-send-email-dwmw@amazon.co.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: Getting objtool to understand retpolines is going to be a bit of a challenge. For now, take advantage of the fact that retpolines are patched in with alternatives. Just read the original (sane) non-alternative instruction, and ignore the patched-in retpoline. This allows objtool to understand the control flow *around* the retpoline, even if it can't yet follow what's inside. This means the ORC unwinder will fail to unwind from inside a retpoline, but will work fine otherwise. Signed-off-by: Josh Poimboeuf Signed-off-by: David Woodhouse --- tools/objtool/check.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++----- tools/objtool/check.h | 2 +- 2 files changed, 57 insertions(+), 7 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index de053fb..f40d46e 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -428,6 +428,40 @@ static void add_ignores(struct objtool_file *file) } /* + * FIXME: For now, just ignore any alternatives which add retpolines. This is + * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline. + * But it at least allows objtool to understand the control flow *around* the + * retpoline. + */ +static int add_nospec_ignores(struct objtool_file *file) +{ + struct section *sec; + struct rela *rela; + struct instruction *insn; + + sec = find_section_by_name(file->elf, ".rela.discard.nospec"); + if (!sec) + return 0; + + list_for_each_entry(rela, &sec->rela_list, list) { + if (rela->sym->type != STT_SECTION) { + WARN("unexpected relocation symbol type in %s", sec->name); + return -1; + } + + insn = find_insn(file, rela->sym->sec, rela->addend); + if (!insn) { + WARN("bad .discard.nospec entry"); + return -1; + } + + insn->ignore_alts = true; + } + + return 0; +} + +/* * Find the destination instructions for all jumps. */ static int add_jump_destinations(struct objtool_file *file) @@ -509,11 +543,18 @@ static int add_call_destinations(struct objtool_file *file) dest_off = insn->offset + insn->len + insn->immediate; insn->call_dest = find_symbol_by_offset(insn->sec, dest_off); + /* + * FIXME: Thanks to retpolines, it's now considered + * normal for a function to call within itself. So + * disable this warning for now. + */ +#if 0 if (!insn->call_dest) { WARN_FUNC("can't find call dest symbol at offset 0x%lx", insn->sec, insn->offset, dest_off); return -1; } +#endif } else if (rela->sym->type == STT_SECTION) { insn->call_dest = find_symbol_by_offset(rela->sym->sec, rela->addend+4); @@ -678,12 +719,6 @@ static int add_special_section_alts(struct objtool_file *file) return ret; list_for_each_entry_safe(special_alt, tmp, &special_alts, list) { - alt = malloc(sizeof(*alt)); - if (!alt) { - WARN("malloc failed"); - ret = -1; - goto out; - } orig_insn = find_insn(file, special_alt->orig_sec, special_alt->orig_off); @@ -694,6 +729,10 @@ static int add_special_section_alts(struct objtool_file *file) goto out; } + /* Ignore retpoline alternatives. */ + if (orig_insn->ignore_alts) + continue; + new_insn = NULL; if (!special_alt->group || special_alt->new_len) { new_insn = find_insn(file, special_alt->new_sec, @@ -719,6 +758,13 @@ static int add_special_section_alts(struct objtool_file *file) goto out; } + alt = malloc(sizeof(*alt)); + if (!alt) { + WARN("malloc failed"); + ret = -1; + goto out; + } + alt->insn = new_insn; list_add_tail(&alt->list, &orig_insn->alts); @@ -1035,6 +1081,10 @@ static int decode_sections(struct objtool_file *file) add_ignores(file); + ret = add_nospec_ignores(file); + if (ret) + return ret; + ret = add_jump_destinations(file); if (ret) return ret; diff --git a/tools/objtool/check.h b/tools/objtool/check.h index 47d9ea7..dbadb30 100644 --- a/tools/objtool/check.h +++ b/tools/objtool/check.h @@ -44,7 +44,7 @@ struct instruction { unsigned int len; unsigned char type; unsigned long immediate; - bool alt_group, visited, dead_end, ignore, hint, save, restore; + bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts; struct symbol *call_dest; struct instruction *jump_dest; struct list_head alts; -- 2.7.4