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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 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 X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8057920002 X-Stat-Signature: wn7h4uzcnxw5mwur7ufh7niq5w8x3o1z X-Rspam-User: X-HE-Tag: 1780926902-535848 X-HE-Meta: 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 TTHXiaNV EIaYIMNz6TViftYRP0b9VPAEJqeM5Nxut2fshTJgVFEvPHL+7/KpPuMDRCyp6og8CclqohvfGwoGXKEsff2hazpLGtRmv2r24OL4LXldZ4s3FIDucnzLz8cs+7KG49Cs6k5kXlZ8YGZTLy1NLCf7VxWfJdJhYe9xRirp2sVZ8DRJRx1xjVuU4vuRFCf+b4+ZRpCODTKLTbU9goMNLcU32qUPxATmZQ1+p3xmzC1nEO1spWDMbWnwQ5zXgilwKlGLaDwG3dGDdSCvLcuAaopc5qW7Ywm72rUwMnvnlJ/fGxClL6mcfA10Cg5O7vA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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