From nobody Sun Feb 8 01:55:54 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 1202D2586ED for ; Fri, 25 Apr 2025 13:39:46 +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=1745588389; cv=none; b=uuXlQYZ4dstETH6f+wT3IpkoZ+iT4q5aG0uurHQ+YbisG/lXyS+MmJfcJL55CiTm8HAyAAHetirJfnOyEWIXKasVD09l+/ZQJWTh1tMnl+8CCHwIwLW5OaPWjbvWYz6FDmxiDXZgrIsiL216OHFYWkDk99g36G6yyJ6AQ7OTzkI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745588389; c=relaxed/simple; bh=yZVSKNRDWKVJJCJw+3fUCprifgbCQie49WUAb0ecBxw=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=LuLv6cfqQfzHlZVqcf9vObzYpQgAMEEaJFRhIQJgcDWqSDiPsPExgHGOidOnRWzbxpEnVwTsSp4tOvg3+4pkmtKjoxyuA4/i2V+8LvpIo9Met03FCrbR0w9hhHlgKCNgbh8LDqUI7eOYVP1nYBqJSTpvGN6MH3+DhaOQiF8TVXk= 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 E5C66168F; Fri, 25 Apr 2025 06:39:40 -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 36E233F59E; Fri, 25 Apr 2025 06:39:45 -0700 (PDT) From: Robin Murphy To: joro@8bytes.org, will@kernel.org, Ioana Ciornei Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Will McVicker Subject: [PATCH] bus: fsl_mc: Fix driver_managed_dma check Date: Fri, 25 Apr 2025 14:39:28 +0100 Message-Id: <20250425133929.646493-3-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_fsl_mc_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/bus/fsl-mc/fsl-mc-bus.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bu= s.c index a8be8cf246fb..67031136ef66 100644 --- a/drivers/bus/fsl-mc/fsl-mc-bus.c +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c @@ -139,9 +139,9 @@ static int fsl_mc_bus_uevent(const struct device *dev, = struct kobj_uevent_env *e =20 static int fsl_mc_dma_configure(struct device *dev) { + const struct device_driver *drv =3D READ_ONCE(dev->driver); struct device *dma_dev =3D dev; struct fsl_mc_device *mc_dev =3D to_fsl_mc_device(dev); - struct fsl_mc_driver *mc_drv =3D to_fsl_mc_driver(dev->driver); u32 input_id =3D mc_dev->icid; int ret; =20 @@ -153,8 +153,8 @@ static int fsl_mc_dma_configure(struct device *dev) else ret =3D acpi_dma_configure_id(dev, DEV_DMA_COHERENT, &input_id); =20 - /* @mc_drv may not be valid when we're called from the IOMMU layer */ - if (!ret && dev->driver && !mc_drv->driver_managed_dma) { + /* @drv may not be valid when we're called from the IOMMU layer */ + if (!ret && drv && !to_fsl_mc_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