From nobody Sun Feb 8 07:44:15 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B32B92580EC for ; Fri, 25 Apr 2025 13:39:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745588386; cv=none; b=srBMWjS2qoeuKnEwXGD1/chG5StDawrNSy2oCXa7CkByXpa58SJ+Yh4FmMdWWfiJnz9HxuPUxGW0270jcweoSlF3Zp6rlGEoiTHOuFkyc9TBywwD8xA50VUII9a+E8dNx6Sp/ka6/lyUDrudT9+OTsU6iSq1CgbrxmHmJaMAY/M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745588386; c=relaxed/simple; bh=S5W6ikEvI/7PxAxitQr+ePFOqbFQvLMa7qlMvpSlxmI=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=cQPntkSkWPB4E+GQ60BF33BQq5JlBYYKAx8iteBjDcISOW5EAckPZs67Z/kKPx4co+OhhUR9BwP9CGpt0oVzojAtFYOCv95j88WtuZ63MKfFFpwZw+N7EOx65TbV/ZPrZ7YSVDgF2OHtK+5ZQJKBtu3VwK0hUAkBaqq+LvPsrG0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DDF31106F; Fri, 25 Apr 2025 06:39:38 -0700 (PDT) Received: from e121345-lin.cambridge.arm.com (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 2EF373F59E; Fri, 25 Apr 2025 06:39:43 -0700 (PDT) From: Robin Murphy To: joro@8bytes.org, will@kernel.org, Nipun Gupta , Nikhil Agarwal Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Will McVicker Subject: [PATCH] cdx: Fix driver_managed_dma check Date: Fri, 25 Apr 2025 14:39:27 +0100 Message-Id: <20250425133929.646493-2-robin.murphy@arm.com> X-Mailer: git-send-email 2.39.2.101.g768bb238c484.dirty 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 Content-Type: text/plain; charset="utf-8" Since it's not currently safe to take device_lock() in the IOMMU probe path, that can race against really_probe() setting dev->driver before attempting to bind. The race itself isn't so bad, since we're only concerned with dereferencing dev->driver itself anyway, but sadly my attempt to implement the check with minimal churn leads to a kind of TOCTOU issue, where dev->driver becomes valid after to_cdx_driver(NULL) is already computed, and thus the check fails to work as intended. Will and I both hit this with the platform bus, but the pattern here is the same, so fix it for correctness too. Reported-by: Will McVicker Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path= ") Signed-off-by: Robin Murphy Reviewed-by: Will McVicker --- drivers/cdx/cdx.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/cdx/cdx.c b/drivers/cdx/cdx.c index 092306ca2541..8aa92a198b71 100644 --- a/drivers/cdx/cdx.c +++ b/drivers/cdx/cdx.c @@ -348,7 +348,7 @@ static void cdx_shutdown(struct device *dev) =20 static int cdx_dma_configure(struct device *dev) { - struct cdx_driver *cdx_drv =3D to_cdx_driver(dev->driver); + const struct device_driver *drv =3D READ_ONCE(dev->driver); struct cdx_device *cdx_dev =3D to_cdx_device(dev); struct cdx_controller *cdx =3D cdx_dev->cdx; u32 input_id =3D cdx_dev->req_id; @@ -360,8 +360,8 @@ static int cdx_dma_configure(struct device *dev) return ret; } =20 - /* @cdx_drv may not be valid when we're called from the IOMMU layer */ - if (!ret && dev->driver && !cdx_drv->driver_managed_dma) { + /* @drv may not be valid when we're called from the IOMMU layer */ + if (!ret && drv && !to_cdx_driver(drv)->driver_managed_dma) { ret =3D iommu_device_use_default_domain(dev); if (ret) arch_teardown_dma_ops(dev); --=20 2.39.2.101.g768bb238c484.dirty