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 38DA3380FD9; Mon, 8 Jun 2026 13:38:05 +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=1780925886; cv=none; b=BpCV2s7d767yMzK+WvIjglnia+2vFS24aeM9tWX71d5osKL/l2bsf6EAfF577wRKw3gUBSu2I9CLnWCGba/fplyY9fsDoGESSzAWr1Fs0Znj8N7X/Gx85bUxR2Hk+szF70EqX18LXuMZi1GKGRoR2NEWOHgg2wV8QstBAzdGNUc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780925886; c=relaxed/simple; bh=b+yEP0xv4aXK3S1JzA9JnwqBMA2Dej+EdhfRuZ2GJrE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=a2YHT2XvCoAbJXwIFQvmqAqTuCkyG89J/Hl4KDHB6F3iCjGo11g97Yi9MXbrp8FTbUtemQO88JkElC3Anr4A8xcYWlujq2n/akmOJbv3tHj4MpCY0nIsQXNWlLe6PleSi88WdtFEsI/Yfr8kLZ72HUMn4CmjP4ZcYV0930lLpdQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LdsaNTFq; 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="LdsaNTFq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EEC331F00893; Mon, 8 Jun 2026 13:38:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780925885; bh=3DmSeVsacdhuO8IPMvgQqcrU2HaMy5DBmzNlEy6t8Sc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LdsaNTFqk669HcLwNMx7JOOX4hWjrgZkdHTXjB2Ko/yB6NiJ84DDHQVDBEtGCh9aw r64054qsJC8nTwPq92DXSOq2JaFL82AgMWM2JKjFNXLF7GmMdagOvVpKkaHZkkF0Sc ExYymswqWwGUOkqPW15y88enuDr+zbmnGJBEGrtn3JmDlWciDbyOvfQwcB9I3Rjtrl 6Qnva4MFkmBkzyVdb+0nOG5DtMDkuijAPhIGhog5+v/GLUgdoMWttyu1XIhbDfylFm zEfP9wYD+cwAkFMdaeH9mDluGhviXSXoJmgY2noGNcbbFo84bUI9tioh3Ud4ssvuMq 1AS4FEKeyZXCQ== Message-ID: <38b49fb2-c2c0-4c7f-ac5c-3e79d54728f0@kernel.org> Date: Mon, 8 Jun 2026 15:38:00 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org 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 , Yiming Qian , Vivek Kasireddy Cc: 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> 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 6/7/26 14:09, Jason Gunthorpe wrote: > On Sun, Jun 07, 2026 at 08:53:18AM +0000, Yiming Qian wrote: >> IOMMU_IOAS_MAP_FILE pins folios from a shmem/tmpfs or hugetlb file and >> uses them as the backing storage for an IOAS mapping. When userspace sets >> IOMMU_IOAS_MAP_WRITEABLE, the resulting IOMMU PTEs allow DMA writes to the >> file-backed folios. > > 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 don't know much about memfd but this seems like a legitimate issue. > > Add those involved with gup.c and the patch adding memfd_pin_folios() > >> { >> struct iopt_pages *pages; >> + int rc; >> + >> + if (writable) { >> + if (!(file->f_mode & FMODE_WRITE)) >> + return ERR_PTR(-EPERM); >> + >> + rc = mapping_map_writable(file->f_mapping); >> + if (rc) >> + return ERR_PTR(rc); >> + } > > We probably need some kind of companion API for memfd_pin_folios(), a > 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. Assume we GUP a page and then munmap, mapping_unmap_writable() would be called while we still have a writable GUP reference. Hm. -- Cheers, David