From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44C46C83000 for ; Wed, 29 Apr 2020 14:33:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 23F24206F0 for ; Wed, 29 Apr 2020 14:33:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726955AbgD2Odf (ORCPT ); Wed, 29 Apr 2020 10:33:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:35494 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726511AbgD2Odf (ORCPT ); Wed, 29 Apr 2020 10:33:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 189E2AC92; Wed, 29 Apr 2020 14:33:32 +0000 (UTC) Date: Wed, 29 Apr 2020 16:33:31 +0200 (CEST) From: Miroslav Benes To: Peter Zijlstra cc: jpoimboe@redhat.com, alexandre.chartre@oracle.com, linux-kernel@vger.kernel.org, jthierry@redhat.com, tglx@linutronix.de, x86@kernel.org, Jann Horn Subject: Re: [PATCH v2 02/14] objtool: Fix ORC vs alternatives In-Reply-To: <20200428191659.499074346@infradead.org> Message-ID: References: <20200428191101.886208539@infradead.org> <20200428191659.499074346@infradead.org> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 28 Apr 2020, Peter Zijlstra wrote: > Jann reported that (for instance) entry_64.o:general_protection has > very odd ORC data: > > 0000000000000f40 : > #######sp:sp+8 bp:(und) type:iret end:0 > f40: 90 nop > #######sp:(und) bp:(und) type:call end:0 > f41: 90 nop > f42: 90 nop > #######sp:sp+8 bp:(und) type:iret end:0 > f43: e8 a8 01 00 00 callq 10f0 > #######sp:sp+0 bp:(und) type:regs end:0 > f48: f6 84 24 88 00 00 00 testb $0x3,0x88(%rsp) > f4f: 03 > f50: 74 00 je f52 > f52: 48 89 e7 mov %rsp,%rdi > f55: 48 8b 74 24 78 mov 0x78(%rsp),%rsi > f5a: 48 c7 44 24 78 ff ff movq $0xffffffffffffffff,0x78(%rsp) > f61: ff ff > f63: e8 00 00 00 00 callq f68 > f68: e9 73 02 00 00 jmpq 11e0 > #######sp:(und) bp:(und) type:call end:0 > f6d: 0f 1f 00 nopl (%rax) > > Note the entry at 0xf41. Josh found this was the result of commit: > > 764eef4b109a ("objtool: Rewrite alt->skip_orig") > > Due to the early return in validate_branch() we no longer set > insn->cfi of the original instruction stream (the NOPs at 0xf41 and > 0xf42) and we'll end up with the above weirdness. > > In other discussions we realized alternatives should be ORC invariant; > that is, due to there being only a single ORC table, it must be valid > for all alternatives. The easiest way to ensure this is to not allow > any stack modifications in alternatives. > > When we enforce this latter observation, we get the property that the > whole alternative must have the same CFI, which we can employ to fix > the former report. > > Fixes: 764eef4b109a ("objtool: Rewrite alt->skip_orig") > Reported-by: Jann Horn > Signed-off-by: Peter Zijlstra (Intel) > --- > tools/objtool/Documentation/stack-validation.txt | 7 ++++ > tools/objtool/check.c | 34 ++++++++++++++++++++++- > 2 files changed, 40 insertions(+), 1 deletion(-) > > --- a/tools/objtool/Documentation/stack-validation.txt > +++ b/tools/objtool/Documentation/stack-validation.txt > @@ -315,6 +315,13 @@ they mean, and suggestions for how to fi > function tracing inserts additional calls, which is not obvious from the > sources). > > +10. file.o: warning: func()+0x5c: alternative modifies stack > + > + This means that an alternative includes instructions that modify the > + stack. The problem is that there is only one ORC unwind table, this means > + that the ORC unwind entries must be valid for each of the alternatives. > + The easiest way to enforce this is to ensure alternative do not contain > + any ORC entries, which in turn implies the above constraint. > > If the error doesn't seem to make sense, it could be a bug in objtool. > Feel free to ask the objtool maintainer for help. > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -2001,6 +2001,11 @@ static int handle_insn_ops(struct instru > list_for_each_entry(op, &insn->stack_ops, list) { > int res; > > + if (insn->alt_group) { > + WARN_FUNC("alternative modifies stack", insn->sec, insn->offset); > + return -1; > + } > + > res = update_cfi_state(insn, &state->cfi, op); > if (res) > return res; > @@ -2177,6 +2182,30 @@ static bool is_branch_to_alternative(str > } > > /* > + * Alternatives should not contain any ORC entries, this in turn means they > + * should not contain any CFI ops, which implies all instructions should have > + * the same same CFI state. > + * > + * It is possible to constuct alternatives that have unreachable holes that go > + * unreported (because they're NOPs), such holes would result in CFI_UNDEFINED > + * states which then results in ORC entries, which we just said we didn't want. > + * > + * Avoid them by copying the CFI entry of the first instruction into the whole > + * alternative. > + */ > +static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn) > +{ > + struct instruction *first_insn = insn; > + int alt_group = insn->alt_group; > + > + sec_for_each_insn_continue(file, insn) { > + if (insn->alt_group != alt_group) > + break; > + insn->cfi = first_insn->cfi; > + } > +} If I am reading this and previous patch correctly... The function would copy cfi only to "orig" alternative (its insn->alts is non-empty, orig_insn->alt_group differs from new_insn->alt_group), right? Would it make sense to do the same for "new" alternative, because of the invariant? It seems to me it is not processed anywhere that way. Am I missing something? Whenever I try to read all this alternatives handling in objtool, I get lost pretty soon. > + > +/* > * Follow the branch starting at the given instruction, and recursively follow > * any other branches (jumps). Meanwhile, track the frame pointer state at > * each instruction and validate all the rules described in > @@ -2234,7 +2263,7 @@ static int validate_branch(struct objtoo > > insn->visited |= visited; > > - if (!insn->ignore_alts) { > + if (!insn->ignore_alts && !list_empty(&insn->alts)) { > bool skip_orig = false; > > list_for_each_entry(alt, &insn->alts, list) { > @@ -2249,6 +2278,9 @@ static int validate_branch(struct objtoo > } > } > > + if (insn->alt_group) > + fill_alternative_cfi(file, insn); > + fill_alternative_cfi() is called here only for orig_insn, isn't it? > if (skip_orig) > return 0; > } Miroslav