From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 2DD49BA21 for ; Fri, 23 Jan 2026 23:06:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769209585; cv=none; b=cHeCwkhe7gTaQy3fQUUhJgWXYkosn6f0iBq8v2gJ7MgN4tx3HbHBCrSNy3Afxn0CGaT2h9L5GT3WL+ZvFxt7nmyXZGzd8u5V4BO54iAa/d8c1taSs4oCTSCsqbfz5QQvNH3U9Gi+XsjH+FwC3BPZtVx4Vr0prEkJCKqiHOs5sjs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769209585; c=relaxed/simple; bh=GE0nt4BxYV6P/FnemHSPkyH88wY102nPdSnYyMP4K8w=; h=Date:To:From:Subject:Message-Id; b=q4V7JGSSxX58FRpThCfZO4OdsD/X8LTsN514f3jj14bD5xQ21YS9WaWEWaJgjJ8QFn39BxMRkAQyvWypOepjl+HiRU5rYc7K60BthtXAlMMf2tskiL34H1fXgdZyr9HoWJhenuqWIrPDNC6DPru2kpxXDGpQiqxqJ18j9JKDIzk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=C3lR1i+/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="C3lR1i+/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B980AC4CEF1; Fri, 23 Jan 2026 23:06:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1769209584; bh=GE0nt4BxYV6P/FnemHSPkyH88wY102nPdSnYyMP4K8w=; h=Date:To:From:Subject:From; b=C3lR1i+//ytis6ebOcPcrT00bZwnSAK9WF08FxvGr6WQ+lMFzSIFBe97o/FTYDfbm SAZi82LannTK9aeYNu0ehpcWerQlLqWM2mdxMmbow9lo/tfuYUyv6JnL0g4wTysQ5x ZF3pGNDyZ0BMQN6Jcejof5ecowrfRdSMinpZvkJE= Date: Fri, 23 Jan 2026 15:06:24 -0800 To: mm-commits@vger.kernel.org,skhawaja@google.com,rppt@kernel.org,pasha.tatashin@soleen.com,jgg@nvidia.com,hughd@google.com,graf@amazon.com,baolin.wang@linux.alibaba.com,pratyush@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-memfd_luo-preserve-file-seals.patch added to mm-new branch Message-Id: <20260123230624.B980AC4CEF1@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: memfd_luo: preserve file seals has been added to the -mm mm-new branch. Its filename is mm-memfd_luo-preserve-file-seals.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memfd_luo-preserve-file-seals.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Pratyush Yadav (Google)" Subject: mm: memfd_luo: preserve file seals Date: Fri, 23 Jan 2026 10:58:51 +0100 File seals are used on memfd for making shared memory communication with untrusted peers safer and simpler. Seals provide a guarantee that certain operations won't be allowed on the file such as writes or truncations. Maintaining these guarantees across a live update will help keeping such use cases secure. These guarantees will also be needed for IOMMUFD preservation with LUO. Normally when IOMMUFD maps a memfd, it pins all its pages to make sure any truncation operations on the memfd don't lead to IOMMUFD using freed memory. This doesn't work with LUO since the preserved memfd might have completely different pages after a live update, and mapping them back to the IOMMUFD will cause all sorts of problems. Using and preserving the seals allows IOMMUFD preservation logic to trust the memfd. Preserve the seals by introducing a new 8-bit-wide bitfield. There are currently only 6 possible seals but 2 extra bits are used to provide room for future expansion. Since the seals are UAPI, it is safe to use them directly in the ABI. Back the 8-bit field with a u64, leaving 56 unused bits. This is done to keep the struct nice and aligned. The unused bits can be used to add new flags later, potentially without even needing to bump the version number. Since the serialization structure is changed, bump the version number to "memfd-v2". Link: https://lkml.kernel.org/r/20260123095854.535058-3-pratyush@kernel.org Signed-off-by: Pratyush Yadav (Google) Cc: Alexander Graf Cc: Baolin Wang Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: Mike Rapoport Cc: Pasha Tatashin Cc: Samiullah Khawaja Signed-off-by: Andrew Morton --- include/linux/kho/abi/memfd.h | 9 ++++++++- mm/memfd_luo.c | 23 +++++++++++++++++++++-- 2 files changed, 29 insertions(+), 3 deletions(-) --- a/include/linux/kho/abi/memfd.h~mm-memfd_luo-preserve-file-seals +++ a/include/linux/kho/abi/memfd.h @@ -60,6 +60,11 @@ struct memfd_luo_folio_ser { * struct memfd_luo_ser - Main serialization structure for a memfd. * @pos: The file's current position (f_pos). * @size: The total size of the file in bytes (i_size). + * @seals: The seals present on the memfd. The seals are UAPI so it is safe + * to directly use them in the ABI. Note: currently there are 6 + * seals possible but this field is 8 bits to leave room for future + * expansion. + * @__reserved: Reserved bits. May be used later to add more flags. * @nr_folios: Number of folios in the folios array. * @folios: KHO vmalloc descriptor pointing to the array of * struct memfd_luo_folio_ser. @@ -67,11 +72,13 @@ struct memfd_luo_folio_ser { struct memfd_luo_ser { u64 pos; u64 size; + u64 seals:8; + u64 __reserved:56; u64 nr_folios; struct kho_vmalloc folios; } __packed; /* The compatibility string for memfd file handler */ -#define MEMFD_LUO_FH_COMPATIBLE "memfd-v1" +#define MEMFD_LUO_FH_COMPATIBLE "memfd-v2" #endif /* _LINUX_KHO_ABI_MEMFD_H */ --- a/mm/memfd_luo.c~mm-memfd_luo-preserve-file-seals +++ a/mm/memfd_luo.c @@ -79,6 +79,8 @@ #include #include #include +#include + #include "internal.h" static int memfd_luo_preserve_folios(struct file *file, @@ -222,7 +224,7 @@ static int memfd_luo_preserve(struct liv struct memfd_luo_folio_ser *folios_ser; struct memfd_luo_ser *ser; u64 nr_folios; - int err = 0; + int err = 0, seals; inode_lock(inode); shmem_freeze(inode, true); @@ -234,8 +236,15 @@ static int memfd_luo_preserve(struct liv goto err_unlock; } + seals = memfd_get_seals(args->file); + if (seals < 0) { + err = seals; + goto err_free_ser; + } + ser->pos = args->file->f_pos; ser->size = i_size_read(inode); + ser->seals = seals; err = memfd_luo_preserve_folios(args->file, &ser->folios, &folios_ser, &nr_folios); @@ -444,13 +453,23 @@ static int memfd_luo_retrieve(struct liv if (!ser) return -EINVAL; - file = memfd_alloc_file("", 0); + /* + * The seals are preserved. Allow sealing here so they can be added + * later. + */ + file = memfd_alloc_file("", MFD_ALLOW_SEALING); if (IS_ERR(file)) { pr_err("failed to setup file: %pe\n", file); err = PTR_ERR(file); goto free_ser; } + err = memfd_add_seals(file, ser->seals); + if (err) { + pr_err("failed to add seals: %pe\n", ERR_PTR(err)); + goto put_file; + } + vfs_setpos(file, ser->pos, MAX_LFS_FILESIZE); file->f_inode->i_size = ser->size; _ Patches currently in -mm which might be from pratyush@kernel.org are memfd-export-alloc_file.patch mm-memfd_luo-use-memfd_alloc_file-instead-of-shmem_file_setup.patch mm-memfd_luo-restore-and-free-memfd_luo_ser-on-failure.patch memfd-export-memfd_addget_seals.patch mm-memfd_luo-preserve-file-seals.patch kho-use-unsigned-long-for-nr_pages.patch kho-simplify-page-initialization-in-kho_restore_page.patch