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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9B1ABC61DB6 for ; Tue, 25 Aug 2026 07:36:15 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id EA68A10E8E7; Tue, 25 Aug 2026 07:36:14 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="QirhcMGi"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 6702310E817 for ; Tue, 25 Aug 2026 07:36:13 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with UTF8SMTP id 04692400D5; Tue, 25 Aug 2026 07:36:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 428D81F000E9; Tue, 25 Aug 2026 07:36:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787643372; bh=epJ5FHpWt7Wp8xRAAUYzuBydWavuFMODafsLE/Yalh4=; h=From:To:Cc:Subject:Date; b=QirhcMGiw4UtOye4lJJTl8L9ZWpb5MyN5CQiIkbIYwU7mcbfuzIM3xiT4SY2UfKsR dMftTrAtVHkx2EhsIG/uyArika0FeiOleqO4qvA3t5V6o7xOiGyAXj0hTD8GqF9uh4 zdlgS6HRu5+9cimTzomgxvJUVEUOzP0gEhEmKbvHkEZMiZN+swiQBpG5EC+xB0XbzR J6LYKnSXOhjFs9RKarnxZVixAbbuz7mMIF3sHE3fj0aExLYzFGPK3l7DboBGdVk4bs GCLxYthxhUA/ziFY/UbihbEP1e53TZljIe/Ma6G3A1d24hVqA3QyIEuVuXXDNGWKqG Lae4LUys1mkFg== From: "syzbot" To: syzkaller-bugs@googlegroups.com, Slawomir Stepien , "David Airlie" , "Dave Airlie" , , "Gerd Hoffmann" , "Maarten Lankhorst" , "Maxime Ripard" , "Simona Vetter" , "Thomas Zimmermann" , Cc: jani.nikula@intel.com, linux-kernel@vger.kernel.org, syzbot@lists.linux.dev Subject: [PATCH] drm/cirrus-qemu: Validate BAR0 size during probe Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Date: Tue, 25 Aug 2026 07:36:12 +0000 (UTC) X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" From: Slawomir Stepien The `cirrus-qemu` driver relies on `CIRRUS_VRAM_SIZE` (4 MB) to validate framebuffer sizes. However, during PCI probe, the driver mapped BAR0 without verifying that its size matches `CIRRUS_VRAM_SIZE`. If a PCI device with a BAR0 smaller than 4 MB is bound to the driver, the mapped VRAM will be smaller than expected. Because validation checks assume 4 MB VRAM, framebuffers larger than the mapped memory can be created. When the display plane is updated (e.g. during release), `cirrus_primary_plane_helper_atomic_update()` copies the framebuffer to VRAM using `drm_fb_memcpy()`. Writing past the end of the mapped I/O memory causes a supervisor write page fault: BUG: unable to handle page fault for address: ffffc9000389c000 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page ... RIP: 0010:memcpy_toio+0x7c/0xe0 arch/x86/lib/iomem.c:110 ... Call Trace: iosys_map_memcpy_to include/linux/iosys-map.h:285 [inline] drm_fb_memcpy+0x325/0x5d0 drivers/gpu/drm/drm_format_helper.c:442 cirrus_primary_plane_helper_atomic_update+0x98a/0xb00 drivers/gpu/drm/tiny/cirrus-qemu.c:358 drm_atomic_helper_commit_planes+0x626/0xea0 drivers/gpu/drm/drm_atomic_helper.c:3038 drm_atomic_helper_commit_tail+0x60/0x510 drivers/gpu/drm/drm_atomic_helper.c:1989 commit_tail+0x2b1/0x3c0 drivers/gpu/drm/drm_atomic_helper.c:2074 drm_atomic_helper_commit+0xa77/0xb10 drivers/gpu/drm/drm_atomic_helper.c:2312 Fix this by validating in `cirrus_pci_probe()` that the PCI BAR0 resource length equals `CIRRUS_VRAM_SIZE`, returning `-ENODEV` if it does not match. Fixes: ab3e023b1b4c ("drm/cirrus: rewrite and modernize driver.") Assisted-by: Gemini:gemini-3.6-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+2442951a6abb004df963@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2442951a6abb004df963 Link: https://syzkaller.appspot.com/ai_job?id=ba262a3a-bccf-4ad8-a1b0-583c55d34fd6 Signed-off-by: Slawomir Stepien --- diff --git a/drivers/gpu/drm/tiny/cirrus-qemu.c b/drivers/gpu/drm/tiny/cirrus-qemu.c index 075221b43..70c995025 100644 --- a/drivers/gpu/drm/tiny/cirrus-qemu.c +++ b/drivers/gpu/drm/tiny/cirrus-qemu.c @@ -602,6 +602,9 @@ static int cirrus_pci_probe(struct pci_dev *pdev, dev = &cirrus->dev; + if (pci_resource_len(pdev, 0) != CIRRUS_VRAM_SIZE) + return -ENODEV; + cirrus->vram = devm_ioremap(&pdev->dev, pci_resource_start(pdev, 0), pci_resource_len(pdev, 0)); if (cirrus->vram == NULL) base-commit: db2ddb87143519e20a95aa36c60b36107b736a58 -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.