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d=suse.de; s=susede2_ed25519; t=1633852418; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=80quR0dJqWEg6rK0iTRkfXVyG+mUHo9ipi86LTLwPGs=; b=kyfRbDllImYT2dBXKL3lRDd9R/HWc45wRjHQHzM3Pe0j2qPhyIruGPIL1u8cmruSxb4a/Z 3HNlv4fy/NsgvBAA== Received: from alsa1.suse.de (alsa1.suse.de [10.160.4.42]) by relay2.suse.de (Postfix) with ESMTP id 3310EA3B83; Sun, 10 Oct 2021 07:53:38 +0000 (UTC) Date: Sun, 10 Oct 2021 09:53:38 +0200 Message-ID: From: Takashi Iwai To: Rich Felker Subject: Re: [musl] Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control In-Reply-To: <20211008120736.GF7074@brightrain.aerifal.cx> References: <20211007160634.GB7074@brightrain.aerifal.cx> <20211007165158.GC7074@brightrain.aerifal.cx> <20211008120736.GF7074@brightrain.aerifal.cx> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII 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, 08 Oct 2021 14:07:39 +0200, Rich Felker wrote: > > 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. OK, I'll submit a proper patch now, to be included in the next PR for 5.15-rc. For further fixes, let's think carefully. thanks, Takashi