From nobody Mon Sep 28 07:17:18 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 54A4E35AC00; Tue, 25 Aug 2026 07:36:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787643374; cv=none; b=BFjAewbq5n4pM57ypZz9KW5memnNNBebOVLcbbNc7WvjIC+m5v3oqA2L2psXXzpjFlrQTqbCTye1F5dgSAK/8xl6jo1p6Z7HY097W3SZwRjtyEWMlGsF29CC3DEX7LQnTnwZeLSunHoQWc8UJHES/nljvsAXUY9IwsBfdbO5CHU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787643374; c=relaxed/simple; bh=NuVNzdcKYmjOrNH/56kv+1PZFsaRb8w1TmOct1QPtYs=; h=From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type:Date; b=ijBLIuWb4rrFzJuNEG8QCspyTxuptkK1P2C0efeUnbkigsI7SsbJIDgcgcLSPcRB8ejDNrZa5QcFdOfBFbivJz88OGB/91S6xsHjt9Ji+ulG3eImU6cUgXl5VgkLkdq8GjvKAeW1cSuSUHqYYAgeiVPI+/PXp79G1n7CyLIskl0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QirhcMGi; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QirhcMGi" 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: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Date: Tue, 25 Aug 2026 07:36:12 +0000 (UTC) Content-Type: text/plain; charset="utf-8" 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=3D2442951a6abb004df963 Link: https://syzkaller.appspot.com/ai_job?id=3Dba262a3a-bccf-4ad8-a1b0-583= c55d34fd6 Signed-off-by: Slawomir Stepien --- diff --git a/drivers/gpu/drm/tiny/cirrus-qemu.c b/drivers/gpu/drm/tiny/cirr= us-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, =20 dev =3D &cirrus->dev; =20 + if (pci_resource_len(pdev, 0) !=3D CIRRUS_VRAM_SIZE) + return -ENODEV; + cirrus->vram =3D devm_ioremap(&pdev->dev, pci_resource_start(pdev, 0), pci_resource_len(pdev, 0)); if (cirrus->vram =3D=3D NULL) base-commit: db2ddb87143519e20a95aa36c60b36107b736a58 --=20 See https://goo.gle/syzbot-ai-patches for information about AI-generated pa= tches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.