From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A8F37C432C3 for ; Mon, 2 Dec 2019 19:01:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7FFEA2464E for ; Mon, 2 Dec 2019 19:01:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575313296; bh=nQ4IeKnwbdMEBhjVbm5AFpcM+nV6NqByl2EJeEQw28c=; h=Date:From:To:Subject:List-ID:From; b=VnFcszFwKDwhYf0BdRNxE4zXgIs9d11UX9M+yo/2z350p2vB+6ZluV6NgcyhhxUxw q1AxsfKsVuT80e5n20aiW3/jfxdp1qP6pJx42FGuApVj7F6j7GKosTymvrwTqsR1U6 dDeg+I4WiCACyLiADEG79/HxoguGgE/vBaXAdJOg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728079AbfLBTBg (ORCPT ); Mon, 2 Dec 2019 14:01:36 -0500 Received: from mail.kernel.org ([198.145.29.99]:42720 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728075AbfLBTBf (ORCPT ); Mon, 2 Dec 2019 14:01:35 -0500 Received: from localhost.localdomain (c-71-198-47-131.hsd1.ca.comcast.net [71.198.47.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7F4B821774; Mon, 2 Dec 2019 19:01:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575313294; bh=nQ4IeKnwbdMEBhjVbm5AFpcM+nV6NqByl2EJeEQw28c=; h=Date:From:To:Subject:From; b=qRHskiz/bF1+ybNcEW3N+wX1a/HYFCMmbSzSJ/fufHbI8zUk2TFV3KpW/bIsNhVzc YBlOnDYW6EIl3h2RPD7OAdjjnpmySNr0PETTyUYh+VnhJ/Yd5tjtVSU7JkYI0eB68Y SG7sYMOHedpfkET2FKmwXKfG5oeskhK5frn3nIHo= Date: Mon, 02 Dec 2019 11:01:34 -0800 From: akpm@linux-foundation.org To: hughd@google.com, joel@joelfernandes.org, mm-commits@vger.kernel.org, ngeoffray@google.com, shuah@kernel.org, stable@vger.kernel.org Subject: [merged] memfd-fix-cow-issue-on-map_private-and-f_seal_future_write-mappings.patch removed from -mm tree Message-ID: <20191202190134.225erV7jP%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: mm, memfd: fix COW issue on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings has been removed from the -mm tree. Its filename was memfd-fix-cow-issue-on-map_private-and-f_seal_future_write-mappings.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Nicolas Geoffray Subject: mm, memfd: fix COW issue on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings F_SEAL_FUTURE_WRITE has unexpected behavior when used with MAP_PRIVATE: A private mapping created after the memfd file that gets sealed with F_SEAL_FUTURE_WRITE loses the copy-on-write at fork behavior, meaning children and parent share the same memory, even though the mapping is private. The reason for this is due to the code below: static int shmem_mmap(struct file *file, struct vm_area_struct *vma) { struct shmem_inode_info *info = SHMEM_I(file_inode(file)); if (info->seals & F_SEAL_FUTURE_WRITE) { /* * New PROT_WRITE and MAP_SHARED mmaps are not allowed when * "future write" seal active. */ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) return -EPERM; /* * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED * read-only mapping, take care to not allow mprotect to revert * protections. */ vma->vm_flags &= ~(VM_MAYWRITE); } ... } And for the mm to know if a mapping is copy-on-write: static inline bool is_cow_mapping(vm_flags_t flags) { return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE; } The patch fixes the issue by making the mprotect revert protection happen only for shared mappings. For private mappings, using mprotect will have no effect on the seal behavior. The F_SEAL_FUTURE_WRITE feature was introduced in v5.1 so v5.3.x stable kernels would need a backport. [akpm@linux-foundation.org: reflow comment, per Christoph] Link: http://lkml.kernel.org/r/20191107195355.80608-1-joel@joelfernandes.org Fixes: ab3948f58ff84 ("mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd") Signed-off-by: Nicolas Geoffray Signed-off-by: Joel Fernandes (Google) Cc: Hugh Dickins Cc: Shuah Khan Cc: Signed-off-by: Andrew Morton --- mm/shmem.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- a/mm/shmem.c~memfd-fix-cow-issue-on-map_private-and-f_seal_future_write-mappings +++ a/mm/shmem.c @@ -2214,11 +2214,14 @@ static int shmem_mmap(struct file *file, return -EPERM; /* - * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED - * read-only mapping, take care to not allow mprotect to revert - * protections. + * Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as + * MAP_SHARED and read-only, take care to not allow mprotect to + * revert protections on such mappings. Do this only for shared + * mappings. For private mappings, don't need to mask + * VM_MAYWRITE as we still want them to be COW-writable. */ - vma->vm_flags &= ~(VM_MAYWRITE); + if (vma->vm_flags & VM_SHARED) + vma->vm_flags &= ~(VM_MAYWRITE); } file_accessed(file); _ Patches currently in -mm which might be from ngeoffray@google.com are