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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ECAC5C4332F for ; Mon, 13 Nov 2023 09:54:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233445AbjKMJyt (ORCPT ); Mon, 13 Nov 2023 04:54:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51374 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231940AbjKMJyr (ORCPT ); Mon, 13 Nov 2023 04:54:47 -0500 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E97510D2 for ; Mon, 13 Nov 2023 01:54:43 -0800 (PST) Received: from localhost (cola.collaboradmins.com [195.201.22.229]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by madras.collabora.co.uk (Postfix) with ESMTPSA id 0E5DB66071C9; Mon, 13 Nov 2023 09:54:41 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1699869282; bh=9bDqGXVfCHUlHc3hp7s0FADRMoSPM6UPpCOfpTvFpJk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=e2nUsO5N4mioF5D9r3oXlR2JsjGkqpom9d2RaVinEXcVe1eS4jchoB4tvp/1/zhJm SxgoR/Ml0EK9e+jaGd7BU6CQq4MFvbdg5Uw2emYy3fqOMQJHk2GztiQ15rboQCvX4X bBAVkLFm0XEe611DKwX4Jc/CGmJuoTNybITKl2drTSkZf5fgiHaBbDLVyZulRES/m0 QNRNUMGmpcPvp1WqhYl52AHwP2228zWuLvjaDSs0ND1GftAua1AEw2lxk+5cZolPOx Miq8/zNSNNAXxlb1ckIBi3PMW2syUksnIxwu6BDbuXMDrrpHxjhm21Brza5nlwbLvL RGXPxrky1YIGQ== Date: Mon, 13 Nov 2023 10:54:38 +0100 From: Boris Brezillon To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?UTF-8?B?S8O2bmln?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v18 22/26] drm/shmem-helper: Don't free refcounted GEM Message-ID: <20231113105438.60896fdf@collabora.com> In-Reply-To: <20231029230205.93277-23-dmitry.osipenko@collabora.com> References: <20231029230205.93277-1-dmitry.osipenko@collabora.com> <20231029230205.93277-23-dmitry.osipenko@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 30 Oct 2023 02:02:01 +0300 Dmitry Osipenko wrote: > Don't free refcounted shmem object to prevent use-after-free bug that > is worse than a memory leak. > > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 6dd087f19ea3..4253c367dc07 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -203,9 +203,10 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > if (obj->import_attach) > drm_prime_gem_destroy(obj, shmem->sgt); > > - drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count)); > - drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count)); > - drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count)); > + if (drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count)) || > + drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count)) || > + drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count))) > + return; I guess you're worried about ->sgt being referenced by the driver after the GEM is destroyed. If we assume drivers don't cache the sgt and always call get_pages_sgt() when they need it that shouldn't be an issue. What we really don't want to release is the pages themselves, but the GPU MMU might still have active mappings pointing to these pages. In any case, I'm not against leaking the GEM object when any of these counters are not zero, but can we at least have a comment in the code explaining why we're doing that, so people don't have to go look at the git history to figure it out. > > drm_gem_object_release(obj); > kfree(shmem);