From mboxrd@z Thu Jan 1 00:00:00 1970 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 C4EF33C2BB9; Mon, 8 Jun 2026 13:55:01 +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=1780926902; cv=none; b=Go3VkHXkMqb0SGNqfeK3uSimny20LVwwY3BX76N18+JpeJKW9EppMTn8avDpjheY9Bhjxyddejf4I5WG0klQjH5vBt6NCDq6cr5Dc+hSnba1NLQW4/j6eTd4UA/xk3dGoQ+qztVAS+nfIlFhIWPvMDeg/4z7YhoVfIV3eEGlIHM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780926902; c=relaxed/simple; bh=uWRkHTdzDOP7kGaWW3lblsasFosr1XgwpOOwG3zlxhM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gyfUqqDFTw0QMiqtFJYKXGQWC0zaZH+NawOOnw6ApM3cZpsUx5vqM0eLBFSPoT9PTtAH9+ehVynalH4bvopg5dBLJLe0wXbtbfM45Lf9mMTwKnDZOyaLeONR2nAVUhBnYCGqgng65PC7YsO5wHcB1bt2J4gdp/tEZp19mCZEcYw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=S12NdG3A; 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="S12NdG3A" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A739B1F0089A; Mon, 8 Jun 2026 13:54:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780926901; bh=H5m0OrUso51DWZxaLpU6hhwt0mtSHqudSR2A+B8zIGk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=S12NdG3AelksNjnH89veVvFl/2lzV2kHIAxrFX+qj12jzWiq6V2AlQUII7baNzB3q g+WhiasGnZ/F6SME10UMZx11bw0nc5uyiKiPbBf99foFWIA9z8VN2fR7Ah2eOdl9Ij qUQTbrda8HJcvBn93PffL43RvuuQfyT6xjstxLaDhdW2pgkD9+kM+UwVSw7N1D7T1M N5o2JbEOtLPIBFropuUfRYsM64F2mqu6LTqnFN/JWmdg4o3jv9Dr+NdiXe8C6kW9xJ rk93de4vJjbnUWRs/IIr0pBWg1xRI8Cnld/l+ltah1GsZqtB3hNj9q3LBw+rdjVbtm 68GnzDmYzgf1A== Message-ID: <4c21bee6-fa58-4d28-b6e5-aefc9dd67cb5@kernel.org> Date: Mon, 8 Jun 2026 15:54:55 +0200 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] iommu/iommufd: Require write access for writable MAP_FILE mappings To: Jason Gunthorpe Cc: Yiming Qian , Vivek Kasireddy , Kevin Tian , Joerg Roedel , Will Deacon , Robin Murphy , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, keenanat2000@gmail.com, linux-mm@kvack.org, Christoph Hellwig , John Hubbard , Peter Xu References: <20260607085320.73274-1-yimingqian591@gmail.com> <20260607120935.GG1962447@nvidia.com> <38b49fb2-c2c0-4c7f-ac5c-3e79d54728f0@kernel.org> <20260608134614.GA4111154@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/8/26 15:46, Jason Gunthorpe wrote: > On Mon, Jun 08, 2026 at 03:38:00PM +0200, David Hildenbrand (Arm) wrote: >> On 6/7/26 14:09, Jason Gunthorpe wrote: >>> >>> This looks like an issue with the API design in memfd_pin_folios(), >>> all users would have a similar bug I think. >> >> Agreed. >> >> Not sure if it should be part of memfd_pin_folios() itself. > > I think it should, drivers should not be open coding this. > > If there is such a thing as a read-only memfd then memfd_pin_folios() > should accept the usual FOLL_WRITE and deal with it internally. I'd rather not want to use FOLL flags (FOLLOW PAGE leftovers, to be renamed to GUP_ on some lucky day) on this interface. But sure, we could add a new set of flags (single flag for now). > >>> start/pin/destroy kind of thing to manage this? >>> >>> It should not be open coded like this. >> >> The permission check is one thing that's clearly missing. >> >> Not sure about the mapping_map_writable() handling ... it's weird to rely on >> that when we are not actually mmaping. > > I don't know anything about sealing, but it shouldn't something check > if it is sealed read-only ? Right. We could do mapping_map_writable() over the duration of the function I guess if we care about concurrent races. Alternative have a new helper that makes sure that mapping->i_mmap_writable is not negative (write denied). > >> Assume we GUP a page and then munmap, mapping_unmap_writable() would be called >> while we still have a writable GUP reference. Hm. > > I suspect the user doing the sealing has to ensure there are no pins > to the memfd before it seals it. If it already let the unsealed memfd > out of its control then it probably cannot be reliably sealed read > only? Yes, that's my assumption. writable pins derived pre-sealing stay valid. -- Cheers, David