From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B871A20309 for ; Wed, 27 Nov 2024 18:46:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732733200; cv=none; b=G3bUQsbBoeu5kchzcTzdmqyqaXpImrkQgGbjNtqg2EtbBoUu+gcPBYtzrADK/9DEqA4Nk2J+dryzpzEj0iZXuQsS4JnXpnhchVJCEEHqpj6fUeVTot9neKU5Ds1Ff43JuiH/Nv5M4IBln3xrZlwFdIuQs+tBBv8LKMGkc9y+C/Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732733200; c=relaxed/simple; bh=FeaJ9o5dKk/pJ22QpvzexYQ9DfIF4qOerEDxjwaj4NA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SXcRSCAn5DgrX0hjIJaS+Cekr0YOHZIAH7vyjKvk2vL3yAJ+CGCci9PKLq9N47mvRffZxybFfkyvMZDcEl1XX3xShkVjMQvKBLgL8o+zIqTtoHks0hjvaBWy7SsCdMLeKfQNvcTApW/f5qwUC82TxDScFGqcxmxjw2H0HWA/YuE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=dm16ea80; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="dm16ea80" Message-ID: <58ee3fdd-ae38-4e6d-9280-cc419d0f28da@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1732733193; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=y30NAdp8Iit8oCWlZl9Z66C9GBmw4GgYnAhj15IS4oo=; b=dm16ea8077L+8mKxebkXO14Ny/02zy5dFEy1sm/JZmnAvAcJNlYi+EtVZBNC7O1ztO6u4I YzF60OkcTyExbdBnoUpLTiGDPeLZsqNLFgYwQUt2Qy84LCXTnQChvJHKzNg0piQjmDDswo GUX8hRSRzoYOGGm/w5Un07PHSfuPu1M= Date: Thu, 28 Nov 2024 02:46:23 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [RFC PATCH] drm/bridge: panel: Use devm_drm_bridge_add() To: Chen-Yu Tsai , Maxime Ripard Cc: Fei Shao , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , AngeloGioacchino Del Regno , David Airlie , Jernej Skrabec , Jonas Karlman , Maarten Lankhorst , Simona Vetter , Thomas Zimmermann , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20241009052402.411978-1-fshao@chromium.org> <20241024-stalwart-bandicoot-of-music-bc6b29@houat> <20241114-gray-corgi-of-youth-f992ec@houat> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Sui Jingfeng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi, On 2024/11/27 17:58, Chen-Yu Tsai wrote: > Revisiting this thread since I just stepped on the same problem on a > different device. > > On Thu, Nov 14, 2024 at 9:12 PM Maxime Ripard wrote: >> On Tue, Oct 29, 2024 at 10:53:49PM +0800, Fei Shao wrote: >>> On Thu, Oct 24, 2024 at 8:36 PM Maxime Ripard wrote: >>>> On Wed, Oct 09, 2024 at 01:23:31PM +0800, Fei Shao wrote: >>>>> In the mtk_dsi driver, its DSI host attach callback calls >>>>> devm_drm_of_get_bridge() to get the next bridge. If that next bridge is >>>>> a panel bridge, a panel_bridge object is allocated and managed by the >>>>> panel device. >>>>> >>>>> Later, if the attach callback fails with -EPROBE_DEFER from subsequent >>>>> component_add(), the panel device invoking the callback at probe time >>>>> also fails, and all device-managed resources are freed accordingly. >>>>> >>>>> This exposes a drm_bridge bridge_list corruption due to the unbalanced >>>>> lifecycle between the DSI host and the panel devices: the panel_bridge >>>>> object managed by panel device is freed, while drm_bridge_remove() is >>>>> bound to DSI host device and never gets called. >>>>> The next drm_bridge_add() will trigger UAF against the freed bridge list >>>>> object and result in kernel panic. >>>>> >>>>> This bug is observed on a MediaTek MT8188-based Chromebook with MIPI DSI >>>>> outputting to a DSI panel (DT is WIP for upstream). >>>>> >>>>> As a fix, using devm_drm_bridge_add() with the panel device in the panel >>>>> path seems reasonable. This also implies a chain of potential cleanup >>>>> actions: >>>>> >>>>> 1. Removing drm_bridge_remove() means devm_drm_panel_bridge_release() >>>>> becomes hollow and can be removed. >>>>> >>>>> 2. devm_drm_panel_bridge_add_typed() is almost emptied except for the >>>>> `bridge->pre_enable_prev_first` line. Itself can be also removed if >>>>> we move the line into drm_panel_bridge_add_typed(). (maybe?) >>>>> >>>>> 3. drm_panel_bridge_add_typed() now calls all the needed devm_* calls, >>>>> so it's essentially the new devm_drm_panel_bridge_add_typed(). >>>>> >>>>> 4. drmm_panel_bridge_add() needs to be updated accordingly since it >>>>> calls drm_panel_bridge_add_typed(). But now there's only one bridge >>>>> object to be freed, and it's already being managed by panel device. >>>>> I wonder if we still need both drmm_ and devm_ version in this case. >>>>> (maybe yes from DRM PoV, I don't know much about the context) >>>>> >>>>> This is a RFC patch since I'm not sure if my understanding is correct >>>>> (for both the fix and the cleanup). It fixes the issue I encountered, >>>>> but I don't expect it to be picked up directly due to the redundant >>>>> commit message and the dangling devm_drm_panel_bridge_release(). >>>>> I plan to resend the official patch(es) once I know what I supposed to >>>>> do next. >>>>> >>>>> For reference, here's the KASAN report from the device: >>>>> ================================================================== >>>>> BUG: KASAN: slab-use-after-free in drm_bridge_add+0x98/0x230 >>>>> Read of size 8 at addr ffffff80c4e9e100 by task kworker/u32:1/69 >>>>> >>>>> CPU: 1 UID: 0 PID: 69 Comm: kworker/u32:1 Not tainted 6.12.0-rc1-next-20241004-kasan-00030-g062135fa4046 #1 >>>>> Hardware name: Google Ciri sku0/unprovisioned board (DT) >>>>> Workqueue: events_unbound deferred_probe_work_func >>>>> Call trace: >>>>> dump_backtrace+0xfc/0x140 >>>>> show_stack+0x24/0x38 >>>>> dump_stack_lvl+0x40/0xc8 >>>>> print_report+0x140/0x700 >>>>> kasan_report+0xcc/0x130 >>>>> __asan_report_load8_noabort+0x20/0x30 >>>>> drm_bridge_add+0x98/0x230 >>>>> devm_drm_panel_bridge_add_typed+0x174/0x298 >>>>> devm_drm_of_get_bridge+0xe8/0x190 >>>>> mtk_dsi_host_attach+0x130/0x2b0 >>>>> mipi_dsi_attach+0x8c/0xe8 >>>>> hx83102_probe+0x1a8/0x368 >>>>> mipi_dsi_drv_probe+0x6c/0x88 >>>>> really_probe+0x1c4/0x698 >>>>> __driver_probe_device+0x160/0x298 >>>>> driver_probe_device+0x7c/0x2a8 >>>>> __device_attach_driver+0x2a0/0x398 >>>>> bus_for_each_drv+0x198/0x200 >>>>> __device_attach+0x1c0/0x308 >>>>> device_initial_probe+0x20/0x38 >>>>> bus_probe_device+0x11c/0x1f8 >>>>> deferred_probe_work_func+0x80/0x250 >>>>> worker_thread+0x9b4/0x2780 >>>>> kthread+0x274/0x350 >>>>> ret_from_fork+0x10/0x20 >>>>> >>>>> Allocated by task 69: >>>>> kasan_save_track+0x40/0x78 >>>>> kasan_save_alloc_info+0x44/0x58 >>>>> __kasan_kmalloc+0x84/0xa0 >>>>> __kmalloc_node_track_caller_noprof+0x228/0x450 >>>>> devm_kmalloc+0x6c/0x288 >>>>> devm_drm_panel_bridge_add_typed+0xa0/0x298 >>>>> devm_drm_of_get_bridge+0xe8/0x190 >>>>> mtk_dsi_host_attach+0x130/0x2b0 >>>>> mipi_dsi_attach+0x8c/0xe8 >>>>> hx83102_probe+0x1a8/0x368 >>>>> mipi_dsi_drv_probe+0x6c/0x88 >>>>> really_probe+0x1c4/0x698 >>>>> __driver_probe_device+0x160/0x298 >>>>> driver_probe_device+0x7c/0x2a8 >>>>> __device_attach_driver+0x2a0/0x398 >>>>> bus_for_each_drv+0x198/0x200 >>>>> __device_attach+0x1c0/0x308 >>>>> device_initial_probe+0x20/0x38 >>>>> bus_probe_device+0x11c/0x1f8 >>>>> deferred_probe_work_func+0x80/0x250 >>>>> worker_thread+0x9b4/0x2780 >>>>> kthread+0x274/0x350 >>>>> ret_from_fork+0x10/0x20 >>>>> >>>>> Freed by task 69: >>>>> kasan_save_track+0x40/0x78 >>>>> kasan_save_free_info+0x58/0x78 >>>>> __kasan_slab_free+0x48/0x68 >>>>> kfree+0xd4/0x750 >>>>> devres_release_all+0x144/0x1e8 >>>>> really_probe+0x48c/0x698 >>>>> __driver_probe_device+0x160/0x298 >>>>> driver_probe_device+0x7c/0x2a8 >>>>> __device_attach_driver+0x2a0/0x398 >>>>> bus_for_each_drv+0x198/0x200 >>>>> __device_attach+0x1c0/0x308 >>>>> device_initial_probe+0x20/0x38 >>>>> bus_probe_device+0x11c/0x1f8 >>>>> deferred_probe_work_func+0x80/0x250 >>>>> worker_thread+0x9b4/0x2780 >>>>> kthread+0x274/0x350 >>>>> ret_from_fork+0x10/0x20 >>>>> >>>>> The buggy address belongs to the object at ffffff80c4e9e000 >>>>> which belongs to the cache kmalloc-4k of size 4096 >>>>> The buggy address is located 256 bytes inside of >>>>> freed 4096-byte region [ffffff80c4e9e000, ffffff80c4e9f000) >>>>> >>>>> The buggy address belongs to the physical page: >>>>> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >>>>> flags: 0x8000000000000040(head|zone=2) >>>>> page_type: f5(slab) >>>>> page: refcount:1 mapcount:0 mapping:0000000000000000 >>>>> index:0x0 pfn:0x104e98 >>>>> raw: 8000000000000040 ffffff80c0003040 dead000000000122 0000000000000000 >>>>> raw: 0000000000000000 0000000000040004 00000001f5000000 0000000000000000 >>>>> head: 8000000000000040 ffffff80c0003040 dead000000000122 0000000000000000 >>>>> head: 0000000000000000 0000000000040004 00000001f5000000 0000000000000000 >>>>> head: 8000000000000003 fffffffec313a601 ffffffffffffffff 0000000000000000 >>>>> head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000 >>>>> page dumped because: kasan: bad access detected >>>>> >>>>> Memory state around the buggy address: >>>>> ffffff80c4e9e000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> ffffff80c4e9e080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> >ffffff80c4e9e100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> ^ >>>>> ffffff80c4e9e180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> ffffff80c4e9e200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>> =================================================================== >>>>> >>>>> Signed-off-by: Fei Shao >>>> I was looking at the driver to try to follow your (awesome btw, thanks) >>>> commit log, and it does have a quite different structure compared to >>>> what we recommend. >>>> >>>> Would following >>>> https://docs.kernel.org/gpu/drm-kms-helpers.html#special-care-with-mipi-dsi-bridges >>>> help? >>> Hi Maxime, >>> >>> Thank you for the pointer. >>> I read the suggested pattern in the doc and compared it with the >>> drivers. If I understand correctly, both the MIPI-DSI host and panel >>> drivers follow the instructions: >>> >>> 1. The MIPI-DSI host driver must run mipi_dsi_host_register() in its probe hook. >>> >> drm/mediatek/mtk_dsi.c runs mipi_dsi_host_register() in the probe hook. >>> 2. In its probe hook, the bridge driver must try to find its MIPI-DSI >>> host, register as a MIPI-DSI device and attach the MIPI-DSI device to >>> its host. >>> >> drm/panel/panel-himax-hx83102.c follows and runs >>> mipi_dsi_attach() at the end of probe hook. >>> 3. In its struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host can >>> now add its component. >>> >> drm/mediatek/mtk_dsi.c calls component_add() in the attach callback. >>> >>> Could you elaborate on the "different structures" you mentioned? >> Yeah, you're right, sorry. >> >>> To clarify my point: the issue is that component_add() may return >>> -EPROBE_DEFER if the component (e.g. DSI encoder) is not ready, >>> causing the panel bridge to be removed. However, drm_bridge_remove() >>> is bound to MIPI-DSI host instead of panel bridge, which owns the >>> actual list_head object. >>> >>> This might be reproducible with other MIPI-DSI host + panel >>> combinations by forcibly returning -EPROBE_DEFER in the host attach >>> hook (verification with another device is needed), so the fix may be >>> required in drm/bridge/panel.c. >> Yeah, I think you're just hitting another bridge lifetime issue, and >> it's not the only one unfortunately. Tying the bridge structure lifetime >> itself to the device is wrong, it should be tied to the DRM device >> lifetime instead. > I think the more immediate issue is that the bridge object's lifetime > and drm_bridge_add/remove are inconsistent when devm_drm_of_get_bridge() > or drmm_of_get_bridge() are used. Well, I think this is more of probe issue of multiple kernel modules. The root issue is that the global bridge list still stores the pointer to *old* the bridge instance which has been freed after the first '-EPROBE_DEFER' happened. The next time the 'drm_bridge_add(&panel_bridge->bridge);' is called, we will deference the *old* NULL pointer. Because it will touch the 'struct drm_bridge::list' field, which's backing memory has been freed. > These helpers tie the bridge add/removal to the device or drm_device > passed in, but internally they call down to drm_panel_bridge_add_typed() > which allocates the bridge object tied to the panel device. When the devm_drm_panel_bridge_add_typed() is passed a pointer of DSI host device, we essentially tie the lifetime of the freshly created drm bridge instance to the DSI host device. But, the 'struct panel_bridge' clearly hint that the bridge instance has the same lifetime with the backing panel, after all, it's the underlying panel baking the bridge. >> But then, the discussion becomes that bridges typically probe outside of >> the "main" DRM device probe path, so you don't have access to the DRM >> device structure until attach at best. >> >> That's why I'm a bit skeptical about your patch. It might workaround >> your issue, but it doesn't actually solve the problem. I guess the best >> way about it would be to convert bridges to reference counting, with the >> device taking a reference at probe time when it allocates the structure >> (and giving it back at remove time), and the DRM device taking one when >> it's attached and one when it's detached. > Without going as far, it's probably better to align the lifecycle of > the two parts. Most other bridge drivers in the kernel have |drm_bridge| > lifecycle tied to their underlying |device|, either with explicit > drm_bridge_{add,remove}() calls in their probe/bind and remove/unbind > callbacks respectively, or with devm_drm_bridge_add in the probe/bind > path. The only ones with a narrower lifecycle are the DSI hosts, which > add the bridge in during host attach and remove it during host detach. > > I'm thinking about fixing the panel_bridge lifecycle such that it is > tied to the panel itself. Maybe that would involve making > devm_drm_of_get_bridge() correctly return bridges even if a panel was > found, and then making the panels create and add panel bridges directly, > possibly within drm_panel_add(). Would that make sense? I think, align the lifetime of the bridge with 'panel->dev' probably helps. Modifying the devm_drm_of_get_bridge() function like the following pattern: ``` struct drm_bridge *devm_drm_of_get_bridge(struct device_node *np, u32 port, u32 endpoint) {     struct drm_bridge *bridge;     struct drm_panel *panel;     int ret;     ret = drm_of_find_panel_or_bridge(np, port, endpoint, &panel, &bridge);     if (ret)         return ERR_PTR(ret);     if (panel)         bridge = devm_drm_panel_bridge_add(panel->dev, panel);     return bridge; } ``` Or alternatively, inline this to drm/mediatek, rename it as mtk_drm_of_get_bridge(). Or alternatively, manage the bridge's lifetime manually. Remove it from the global bridge list if errors happen. > > Thanks > ChenYu > >> It's much more involved than just another helper though :/ >> >> Maxime -- Best regards, Sui