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=-9.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 13FCCFC6195 for ; Thu, 7 Nov 2019 19:54:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CDC1921D7B for ; Thu, 7 Nov 2019 19:54:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="MF2KEhws" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CDC1921D7B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=joelfernandes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 68D676B0003; Thu, 7 Nov 2019 14:54:05 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 617806B0006; Thu, 7 Nov 2019 14:54:05 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4DEBC6B0007; Thu, 7 Nov 2019 14:54:05 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0174.hostedemail.com [216.40.44.174]) by kanga.kvack.org (Postfix) with ESMTP id 351B76B0003 for ; Thu, 7 Nov 2019 14:54:05 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id CC9742C8A for ; Thu, 7 Nov 2019 19:54:04 +0000 (UTC) X-FDA: 76130532408.21.end27_40a218e790c0c X-HE-Tag: end27_40a218e790c0c X-Filterd-Recvd-Size: 5542 Received: from mail-pg1-f196.google.com (mail-pg1-f196.google.com [209.85.215.196]) by imf07.hostedemail.com (Postfix) with ESMTP for ; Thu, 7 Nov 2019 19:54:04 +0000 (UTC) Received: by mail-pg1-f196.google.com with SMTP id q22so2689335pgk.2 for ; Thu, 07 Nov 2019 11:54:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=Ghp1ccQ5fcbrX+RPWdRWrW5V+/l6RykYTQKYb1Z+Wp4=; b=MF2KEhwsFOY2JznvdfjXOUNj6W3qYNeau+VKgjLdGcoHKMwypDOQ9+KNmwpoguPBnA 7i/obFhGjyKDKsUMxeH64dpCWx1uMOpGLtazJ2WOFQJj2EgXR2EKcxlrJHXs+HFIxiKU AjzqDaEAAzRnfgvLsssB5KV+gpsE0RcbDcp+E= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=Ghp1ccQ5fcbrX+RPWdRWrW5V+/l6RykYTQKYb1Z+Wp4=; b=qX2xxfwXNh0xiO38RAYh3m36OEGcMTOyRvnNhLp849jA895XrUds7durBnkQk706bF T2CR1qcT7n80USLNVCgxj2xjjllwJmtpm+m/Yj+tAWtKxdGbYgDC/JaN0igUN7I8RREO W8/TR8eKvcS9qqspyy6B/wE2RDZ2Et4ObPa97WGQVpVEOHhqRFWCDRWYu+gaRQi7FLMQ p3aDP5UX4ExQHP2+unD1jebtd2Aqvs3WFw4tuuAQEPow0GcRmhWu3DxYKdbndeBW/PBB diLSlBBM7uNUoqAR55BmEwo1F8PN/pRUy+G8M0TZ/GHnGOUOZMj614UBaWjCWq1uSWCC ISQA== X-Gm-Message-State: APjAAAVNppYN5bA2w4L2a9MjwPD2RBGb272hQldLAs7J5Nu6hKwjgfgY wYlKbOsgDuUuDo946FADrZvpBg== X-Google-Smtp-Source: APXvYqxa4V3GDy6MxEr8e4GyHJt30Yq7/f7FjZfuQPYkIlqBQ0ZxitLHpBCbWZAaGGArGLkuPC825w== X-Received: by 2002:a63:f852:: with SMTP id v18mr4706535pgj.71.1573156442796; Thu, 07 Nov 2019 11:54:02 -0800 (PST) Received: from joelaf.cam.corp.google.com ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id y2sm3365870pfe.126.2019.11.07.11.54.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Nov 2019 11:54:02 -0800 (PST) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: Nicolas Geoffray , kernel-team@android.com, Joel Fernandes , Andrew Morton , Hugh Dickins , linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Shuah Khan Subject: [PATCH 1/2] memfd: Fix COW issue on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings Date: Thu, 7 Nov 2019 14:53:54 -0500 Message-Id: <20191107195355.80608-1-joel@joelfernandes.org> X-Mailer: git-send-email 2.24.0.rc1.363.gb1bccd3e3d-goog MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Nicolas Geoffray 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 =3D SHMEM_I(file_inode(file)); if (info->seals & F_SEAL_FUTURE_WRITE) { /* * New PROT_WRITE and MAP_SHARED mmaps are not allowed wh= en * "future write" seal active. */ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WR= ITE)) return -EPERM; /* * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SH= ARED * read-only mapping, take care to not allow mprotect to = revert * protections. */ vma->vm_flags &=3D ~(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)) =3D=3D 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. Cc: kernel-team@android.com Signed-off-by: Nicolas Geoffray Signed-off-by: Joel Fernandes (Google) --- Google bug: 143833776 mm/shmem.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 447fd575587c..6ac5e867ef13 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2214,11 +2214,14 @@ static int shmem_mmap(struct file *file, struct v= m_area_struct *vma) return -EPERM; =20 /* - * 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 &=3D ~(VM_MAYWRITE); + if (vma->vm_flags & VM_SHARED) + vma->vm_flags &=3D ~(VM_MAYWRITE); } =20 file_accessed(file); --=20 2.24.0.rc1.363.gb1bccd3e3d-goog