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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88D1BC433EF for ; Sun, 10 Oct 2021 07:53:51 +0000 (UTC) Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0B0A061074 for ; Sun, 10 Oct 2021 07:53:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0B0A061074 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=libc.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=alsa-project.org Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id 6BBE81694; Sun, 10 Oct 2021 09:52:59 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz 6BBE81694 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1633852429; bh=x9H7aKNnWaIhqnE0hsUkqWOwklLxC0c7oLb2mhgQPbI=; h=Date:From:To:Subject:References:In-Reply-To:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=HjASrk/vmWORuGkfb0Pcvtjc3Ttwk1tHTDoRSa7H+JjjowojxynPds2utONh9ftC4 eb9PDpwFdOpPZLLcyoXA7/dhC897DywBg9wwFfcOEZtYwE0EtTTSzN9FhEA5JUVMyQ Q0dS1gYeS1SrYsYXqr2ZR37mpEiduiN+YpvZTCeA= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id 5D501F8051B; Sun, 10 Oct 2021 09:49:39 +0200 (CEST) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 513A7F80246; Fri, 8 Oct 2021 14:07:49 +0200 (CEST) Received: from brightrain.aerifal.cx (brightrain.aerifal.cx [216.12.86.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id 5967FF80124 for ; Fri, 8 Oct 2021 14:07:41 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 5967FF80124 Date: Fri, 8 Oct 2021 08:07:39 -0400 From: Rich Felker To: Takashi Iwai Subject: Re: [musl] Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control Message-ID: <20211008120736.GF7074@brightrain.aerifal.cx> References: <20211007160634.GB7074@brightrain.aerifal.cx> <20211007165158.GC7074@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Mailman-Approved-At: Sun, 10 Oct 2021 09:49:29 +0200 Cc: ALSA Development Mailing List , Arnd Bergmann , Baolin Wang , y2038 Mailman List , Linux Kernel Mailing List , musl@lists.openwall.com, Takashi Iwai , Michael Forney , Mark Brown , Baolin Wang X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" On Fri, Oct 08, 2021 at 01:11:34PM +0200, Takashi Iwai wrote: > On Fri, 08 Oct 2021 11:24:39 +0200, > Arnd Bergmann wrote: > > > > On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai wrote: > > > On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote: > > > > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote: > > > > > > @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr { > > > #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN) > > > typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)]; > > > typedef char __pad_after_uframe[0]; > > > +typedef char __pad_before_u32[4]; > > > +typedef char __pad_after_u32[0]; > > > #endif > > > > > > #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN) > > > typedef char __pad_before_uframe[0]; > > > typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)]; > > > +typedef char __pad_before_u32[0]; > > > +typedef char __pad_after_u32[4]; > > > #endif > > > > I think these should remain unchanged, the complex expression was intentionally > > done so the structures are laid out the same way on 64-bit > > architectures, so that > > the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit > > and 64-bit architectures. > > That was explicitly defined, but OK, this isn't necessarily defined > here. > > > > @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream, > > > memset(&sync_ptr, 0, sizeof(sync_ptr)); > > > if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags))) > > > return -EFAULT; > > > - if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control))) > > > - return -EFAULT; > > > + if (buggy_control) { > > > + if (copy_from_user(&sync_ptr.c.control_api_2_0_15, > > > + &(_sync_ptr->c.control_api_2_0_15), > > > + sizeof(sync_ptr.c.control_api_2_0_15))) > > > + return -EFAULT; > > > + } else { > > > + if (copy_from_user(&sync_ptr.c.control, > > > + &(_sync_ptr->c.control), > > > + sizeof(sync_ptr.c.control))) > > > + return -EFAULT; > > > + } > > > > The problem I see with this is that it might break musl's ability to > > emulate the new > > interface on top of the old (time32) one for linux-4.x and older > > kernels, as the conversion > > function is no longer stateless but has to know the negotiated > > interface version. > > > > It's probably fine as long as we can be sure that the 2.0.16+ API > > version only gets > > negotiated if both the kernel and user sides support it, and musl only emulates > > the 2.0.15 API version from the current kernels. > > > > I've tried to understand this part of musl's convert_ioctl_struct(), but I just > > can't figure out whether it does the conversion based the on the layout that > > is currently used in the kernel, or based on the layout we should have been > > using, and would use with the above fix. Rich, can you help me here? > > So, at this moment, I'm not sure whether we should correct the struct > at all. This will lead to yet more breakage, and basically the struct > itself *works* -- the only bug is in 32bit compat handling in the > kernel (again). > > The below is a revised kernel patch (again untested), just correcting > the behavior of 32bit compat mode. 32bit apps on 32bit kernel work > fine as is, as well as 64bit apps on 64bit kernel. I'm perfectly okay with this if Arnd is! It's probably the least invasive and has the least long-term maintenance cost and fallout on other projects. Rich