From owner-freebsd-hackers@freebsd.org Fri Mar 17 11:27:55 2017 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E405ED0E0BC for ; Fri, 17 Mar 2017 11:27:55 +0000 (UTC) (envelope-from killing@multiplay.co.uk) Received: from mail-wr0-x22d.google.com (mail-wr0-x22d.google.com [IPv6:2a00:1450:400c:c0c::22d]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 7088E1183 for ; Fri, 17 Mar 2017 11:27:55 +0000 (UTC) (envelope-from killing@multiplay.co.uk) Received: by mail-wr0-x22d.google.com with SMTP id g10so49934785wrg.2 for ; Fri, 17 Mar 2017 04:27:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=multiplay-co-uk.20150623.gappssmtp.com; s=20150623; h=subject:to:references:cc:from:message-id:date:user-agent :mime-version:in-reply-to; bh=cqHQcOrGywrnM1zYyp0h/H5nrcCGyziVuMFBUr/l70I=; b=vb8S8U6WqmB534b90xq0+l4B2GLRce/W3j0uDi4n8czJkA9HtB3btjYfWCZEcZ3LF+ NDR67JVEkIV6ALT0LrenWbdCXjnIxWGNkb/qOAnAYPVlHhQrfAFjsTI13vWIzIYQ1396 n6trToWJAq48wBEkOMrsR3g6WfEb4k3k7oCRb/pITVs2rwYRdYdN29IaWZu4CNXRR7wU +RGtH3UhpM6gn0G8OYUVXgZsvuRtNqnnG/lYWWvmYhY65ey2YAoTUqyP9ZiB0pyQPKzY pxKfwFnTanxxItnnuo+WYCvydvvFOi6cBOHfB8ZLXwxE9XDB34adlvTznESOSgMq/Xyz 5Rmw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:cc:from:message-id:date :user-agent:mime-version:in-reply-to; bh=cqHQcOrGywrnM1zYyp0h/H5nrcCGyziVuMFBUr/l70I=; b=uF9Y13mDhxqEyWUYxFVrZUUcrrYbQl55ov8Bs+YUvichFOCiMIa/hD3C8gHl5a+EB8 Y9B6o4Mr704ZTytKefzJtyCl/QmKhhlbp2zsIyE4XQTNAsKrqZmYvntd6xB/kHXAMsj+ whgNoWc3bCvWTdmtAlcMMV+o2hGuS1oRdyP5LsLg0YAdHFjy+P5wFQEQOw2fbZtgT18r FnK+m+PvRWjQ0SZrHpVkLNWpmziAFeNi/qe7faaj54TxwSMrOkqx/kG7hqlGetLfJMqa JYza4X6JAidJX1Pswy0SSv2brH8+DY2XmftVlkVQWZGaLS1wUeKS23OrzEWsvHu3VZO9 WL5A== X-Gm-Message-State: AFeK/H3JvZl8zMjTTzmGg7QMg4jXwyvWcfSOut4QQ1GEjlPiE/pn05kPjrHYfCAhbjyI2nTE X-Received: by 10.223.155.147 with SMTP id d19mr9936384wrc.99.1489750073814; Fri, 17 Mar 2017 04:27:53 -0700 (PDT) Received: from [10.10.1.58] ([185.97.61.26]) by smtp.gmail.com with ESMTPSA id 17sm9643125wru.16.2017.03.17.04.27.52 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Mar 2017 04:27:52 -0700 (PDT) Subject: Re: Help needed to identify golang fork / memory corruption issue on FreeBSD To: Konstantin Belousov References: <27e1a828-5cd9-0755-50ca-d7143e7df117@multiplay.co.uk> <20161206125919.GQ54029@kib.kiev.ua> <8b502580-4d2d-1e1f-9e05-61d46d5ac3b1@multiplay.co.uk> <20161206143532.GR54029@kib.kiev.ua> <18b40a69-4460-faf2-c0ce-7491eca92782@multiplay.co.uk> <20170317082333.GP16105@kib.kiev.ua> Cc: "K. Macy" , "freebsd-hackers@freebsd.org" From: Steven Hartland Message-ID: <180a601b-5481-bb41-f7fc-67976aabe451@multiplay.co.uk> Date: Fri, 17 Mar 2017 11:27:52 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170317082333.GP16105@kib.kiev.ua> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 17 Mar 2017 11:27:56 -0000 On 17/03/2017 08:23, Konstantin Belousov wrote: > On Fri, Mar 17, 2017 at 06:30:49AM +0000, Steven Hartland wrote: >> Ok I think I've identified the cause. >> >> If an alternative signal stack is applied to a non-main thread and that >> thread calls execve then the signal stack is not cleared. >> >> This results in all sorts of badness. >> >> Full details, including a small C reproduction case can be found here: >> https://github.com/golang/go/issues/15658#issuecomment-287276856 >> >> So looks like its kernel bug. If anyone has an ideas about that before I >> look tomorrow that would be appreciated. > Yes, there is definitely a kernel bug, which should be fixed by the patch > below. > > Still, what I saw when I looked at the issue, is not quite resembling > potential consequences of the bug. Using wrong memory for signal stack > would result either in much more significant memory corruption if the > alt stack range is mapped and used for something unrelated, or in killed > process on signal delivery, if the range is not mapped. While I saw a > systematic 'off by 0x10' in some gc structures. > > Anyway, patch for the issue you identified: > > diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c > index 29d5dd4b132..9bf3ba66f5c 100644 > --- a/sys/kern/kern_sig.c > +++ b/sys/kern/kern_sig.c > @@ -976,7 +976,6 @@ execsigs(struct proc *p) > * and are now ignored by default). > */ > PROC_LOCK_ASSERT(p, MA_OWNED); > - td = FIRST_THREAD_IN_PROC(p); > ps = p->p_sigacts; > mtx_lock(&ps->ps_mtx); > while (SIGNOTEMPTY(ps->ps_sigcatch)) { > @@ -1007,6 +1006,8 @@ execsigs(struct proc *p) > * Reset stack state to the user stack. > * Clear set of signals caught on the signal stack. > */ > + td = curthread; > + MPASS(td->td_proc == p); > td->td_sigstk.ss_flags = SS_DISABLE; > td->td_sigstk.ss_size = 0; > td->td_sigstk.ss_sp = 0; Thanks Kostik, pretty obvious now looking at :) Testing here we've seen all sorts of corruption looking things, mainly around random signals from SIGILL to SIGSEGV but also random kernel messages including: pid 4603 (test): sigreturn copying xfpustate failed pid 5013 (test): sigreturn xfpusave_len = 0x44d9bb I'm currently running a test, but its looking good as the test case usually crashes in a matter of seconds. Would you mind if I committed it? I'm guessing given its nature this is something we'd want MFC'ed and Errata's issued for all supported versions? Regards Steve