From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: ARC-Seal: i=1; a=rsa-sha256; t=1516649252; cv=none; d=google.com; s=arc-20160816; b=uWV0YpzwRq0eng8ATzI5qMgAs07GfdC/k3yDjUirbUlOnGdjN++xkvYeTsq0XFjvbg s7PrQfjHisX1PiUmPoGDPvgbhv3Toik4MZMoZCsK+Ozu1VfFQ3YT0gKyTrYj5gLFp3GF V8L8YTrkC6dZSgEMoiaKYQbZnyhniNDiJc2jF9gd+6OmePpZCtzv/Aj/KtHKSATc/lI6 YJ3QM0Gw8VZ/lbjnbTMgx8JOfWifrUaAFikAJhX/irSVe1nykZy8QbbX1dWlQfqzmte4 JC4Uw0H5JKpc71coVrg9983tnSzo/jm2ITJS5U/rZry5gERX5goulkX6TDVURExPLzOy 2yFw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:sender:dkim-signature :arc-authentication-results; bh=C3pdhKT9HLcrqqNkhyiLbdF7ZMRcTU/5NyZS3AC/p8g=; b=fgOWNZ6114VsaMrNRhFY0ENLmD1gBwKJW/SJ7V0J+oGQoT8RgS6jwz2siwkBVeDMUz 3jqtUQAe/Ue7Lx/Ek9LB/TmoUUF8Kz7uJl0ht5sKwiBJKbMqXad/ZmasyJtCSPQVuuMV M6feLxmR38fsw8KhGSFJbqi3lCM1oNaznKxG/j9F3OYoES58bIcwgwO1SNsYq0vxhVin 0jv3kmacYRBeBwsjeCN1E8nPq0T91euasIY8aV9iWCbFM18la2OKWv9O0sRdxQizUSKI qhQB+9rR2XivDb1Nht+Tv/rJQegq+ovNjr5EL299frFptMMNB4btqp/wazfFGvWV1tf2 9w+g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=G/8F9HcL; spf=pass (google.com: domain of groeck7@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=groeck7@gmail.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=G/8F9HcL; spf=pass (google.com: domain of groeck7@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=groeck7@gmail.com X-Google-Smtp-Source: AH8x224HN5yXQISUXHFnjIV/ktz3610LfOOVix+LTuUQjBNuJNHK8bOzToNRzCJTbo4/R1yntSREpw== Sender: Guenter Roeck Date: Mon, 22 Jan 2018 11:27:29 -0800 From: Guenter Roeck To: Josh Poimboeuf Cc: "Woodhouse, David" , Andi Kleen , 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 Subject: Re: [v8,02/12] objtool: Allow alternatives to be ignored Message-ID: <20180122192729.GA28236@roeck-us.net> References: <1515707194-20531-3-git-send-email-dwmw@amazon.co.uk> <20180118190931.GA27143@roeck-us.net> <20180118193315.zrrya7qo6kf7pmzp@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180118193315.zrrya7qo6kf7pmzp@treble> User-Agent: Mutt/1.5.24 (2015-08-30) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1589334210253041473?= X-GMAIL-MSGID: =?utf-8?q?1590322006083828559?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Jan 18, 2018 at 01:33:15PM -0600, Josh Poimboeuf wrote: > On Thu, Jan 18, 2018 at 11:09:31AM -0800, Guenter Roeck wrote: > > Hi folks, > > > > On Thu, Jan 11, 2018 at 09:46:24PM +0000, Woodhouse, David wrote: > > > 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 > > > > This crashes for me in is_fentry_call(). > > > > Program received signal SIGSEGV, Segmentation fault. > > is_fentry_call (insn=, insn=) at check.c:1113 > > 1113 if (insn->type == INSN_CALL && > > (gdb) info stack > > #0 is_fentry_call (insn=, insn=) at check.c:1113 > > #1 validate_branch (file=0x7ffffff7e440, first=0x7ffffff7e128, state=...) at check.c:1747 > > #2 0x0000000000404bd3 in validate_branch (file=0x7ffffff7e440, first=0x7ffffff7e128, state=...) at check.c:1770 > > #3 0x0000000000406783 in validate_functions (file=) at check.c:1933 > > #4 check (_objname=0x6bb9d0 "", _no_fp=40, no_unreachable=4, orc=false) at check.c:2006 > > #5 0x00000000004021c1 in handle_internal_command (argv=0x7fffffffe5c0, argc=4) at objtool.c:108 > > #6 main (argc=4, argv=0x7fffffffe5c0) at objtool.c:131 > > > > This is not entirely surprising, since insn->call_dest is NULL and > > is_fentry_call() doesn't expect that. > > > > How is this supposed to work ? What am I missing ? > > Not sure, does your gcc have retpolines? Give me your .o file and I can > diagnose it. > > I intended to have an error msg instead of a seg fault for this > situation, just haven't had a chance to improve that yet in the midst of > all the hoopla. > Any updates ? I reverted thee offending patch from our latest stable tree merge, but that doesn't really solve the issue. Thanks, Guenter