From patchwork Thu Oct 18 06:59:07 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joel Fernandes X-Patchwork-Id: 10646773 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2F9D117DE for ; Thu, 18 Oct 2018 06:59:21 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 22143287BB for ; Thu, 18 Oct 2018 06:59:21 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1643A287F4; Thu, 18 Oct 2018 06:59:21 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 84B81287F3 for ; Thu, 18 Oct 2018 06:59:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726031AbeJRO6v (ORCPT ); Thu, 18 Oct 2018 10:58:51 -0400 Received: from mail-pf1-f196.google.com ([209.85.210.196]:45812 "EHLO mail-pf1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727359AbeJRO6v (ORCPT ); Thu, 18 Oct 2018 10:58:51 -0400 Received: by mail-pf1-f196.google.com with SMTP id u12-v6so14409584pfn.12 for ; Wed, 17 Oct 2018 23:59:18 -0700 (PDT) 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=Xear+RLNnBEI0/eVpUZWOmlWkAdxU+7aAlsATSKFP7M=; b=Wfm7WNtnSe1mOFGfqKBdRntjsGjuttEpU10k9RKeog5WXJ4GJeEB8W4LkPkkB6p5qt m0VAfP1IGy9EfgWauzMhEfHkXjnITorsjoe5qct0+kAEb7FmQ6lrAFpoRbx0WKmmIbsv cBjHAtotUSQYxzv+ZijepTDA6aV5uMFoaR+FI= 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=Xear+RLNnBEI0/eVpUZWOmlWkAdxU+7aAlsATSKFP7M=; b=p+ewanczqEY4KRi1GTIZPAHLxisyBnsAC9Y9gs+siUP0vmSbr/7J/2TthjeOXJ5RAO d3uczccHtb5JcfFsofEOXcLA4OxDAI8abBqtWu9jT/xBhYzzqDttxatfHVSJAJFb3bjK fdwOsunzMgZuFvLr1dR/ZSqT/fB9z/I0TtqEm9+/n8Shrid+roOAMNCOf0ScWiVph9Rt k/yzcYEm18uKek8NjL1T1EA1xPE4R2OzIizxTLRARr2aBhNJ8pvt4RnwQ07Hhw4oBSMa RFwE9J1iURxSCYiyZQffMRbZymx/30uwWvQXROB3Euzqre0AFKBP51kNaEjgIfg3vPVl fG3A== X-Gm-Message-State: ABuFfoji8HYch0SyZEm+5CQzyRlhfkgkXZ8TZ88fircmf+Vxqv9KKlhR rGuyOBzT7sFGwxC0iXs4A4yGSA== X-Google-Smtp-Source: ACcGV61xNVH+I+unnVa85HggpBCokX4PPakDnkgxaXbTohriKoGLxj+MmqZCLQw34fZ/oUzP7/SshA== X-Received: by 2002:a63:f744:: with SMTP id f4-v6mr27668756pgk.410.1539845957462; Wed, 17 Oct 2018 23:59:17 -0700 (PDT) Received: from joelaf.mtv.corp.google.com ([2620:0:1000:1601:3aef:314f:b9ea:889f]) by smtp.gmail.com with ESMTPSA id r23-v6sm21580750pfh.79.2018.10.17.23.59.15 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Oct 2018 23:59:16 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org Cc: kernel-team@android.com, "Joel Fernandes (Google)" , jreck@google.com, john.stultz@linaro.org, tkjos@google.com, gregkh@linuxfoundation.org, hch@infradead.org, Al Viro , Andrew Morton , dancol@google.com, "J. Bruce Fields" , Jeff Layton , linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, marcandre.lureau@redhat.com, Mike Kravetz , minchan@kernel.org, Shuah Khan , Thomas Gleixner Subject: [PATCH v3 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd Date: Wed, 17 Oct 2018 23:59:07 -0700 Message-Id: <20181018065908.254389-1-joel@joelfernandes.org> X-Mailer: git-send-email 2.19.1.331.ge82ca0e54c-goog MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Android uses ashmem for sharing memory regions. We are looking forward to migrating all usecases of ashmem to memfd so that we can possibly remove the ashmem driver in the future from staging while also benefiting from using memfd and contributing to it. Note staging drivers are also not ABI and generally can be removed at anytime. One of the main usecases Android has is the ability to create a region and mmap it as writeable, then add protection against making any "future" writes while keeping the existing already mmap'ed writeable-region active. This allows us to implement a usecase where receivers of the shared memory buffer can get a read-only view, while the sender continues to write to the buffer. See CursorWindow documentation in Android for more details: https://developer.android.com/reference/android/database/CursorWindow This usecase cannot be implemented with the existing F_SEAL_WRITE seal. To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal which prevents any future mmap and write syscalls from succeeding while keeping the existing mmap active. The following program shows the seal working in action: #include #include #include #include #include #include #include #define F_SEAL_FUTURE_WRITE 0x0010 #define REGION_SIZE (5 * 1024 * 1024) int memfd_create_region(const char *name, size_t size) { int ret; int fd = syscall(__NR_memfd_create, name, MFD_ALLOW_SEALING); if (fd < 0) return fd; ret = ftruncate(fd, size); if (ret < 0) { close(fd); return ret; } return fd; } int main() { int ret, fd; void *addr, *addr2, *addr3, *addr1; ret = memfd_create_region("test_region", REGION_SIZE); printf("ret=%d\n", ret); fd = ret; // Create map addr = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (addr == MAP_FAILED) printf("map 0 failed\n"); else printf("map 0 passed\n"); if ((ret = write(fd, "test", 4)) != 4) printf("write failed even though no future-write seal " "(ret=%d errno =%d)\n", ret, errno); else printf("write passed\n"); addr1 = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (addr1 == MAP_FAILED) perror("map 1 prot-write failed even though no seal\n"); else printf("map 1 prot-write passed as expected\n"); ret = fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE | F_SEAL_GROW | F_SEAL_SHRINK); if (ret == -1) printf("fcntl failed, errno: %d\n", errno); else printf("future-write seal now active\n"); if ((ret = write(fd, "test", 4)) != 4) printf("write failed as expected due to future-write seal\n"); else printf("write passed (unexpected)\n"); addr2 = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (addr2 == MAP_FAILED) perror("map 2 prot-write failed as expected due to seal\n"); else printf("map 2 passed\n"); addr3 = mmap(0, REGION_SIZE, PROT_READ, MAP_SHARED, fd, 0); if (addr3 == MAP_FAILED) perror("map 3 failed\n"); else printf("map 3 prot-read passed as expected\n"); } The output of running this program is as follows: ret=3 map 0 passed write passed map 1 prot-write passed as expected future-write seal now active write failed as expected due to future-write seal map 2 prot-write failed as expected due to seal : Permission denied map 3 prot-read passed as expected Cc: jreck@google.com Cc: john.stultz@linaro.org Cc: tkjos@google.com Cc: gregkh@linuxfoundation.org Cc: hch@infradead.org Reviewed-by: John Stultz Signed-off-by: Joel Fernandes (Google) --- v1->v2: No change, just added selftests to the series. manpages are ready and I'll submit them once the patches are accepted. v2->v3: Updated commit message to have more support code (John Stultz) Renamed seal from F_SEAL_FS_WRITE to F_SEAL_FUTURE_WRITE (Christoph Hellwig) Allow for this seal only if grow/shrink seals are also either previous set, or are requested along with this seal. (Christoph Hellwig) Added locking to synchronize access to file->f_mode. (Christoph Hellwig) include/uapi/linux/fcntl.h | 1 + mm/memfd.c | 22 +++++++++++++++++++++- 2 files changed, 22 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 6448cdd9a350..a2f8658f1c55 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -41,6 +41,7 @@ #define F_SEAL_SHRINK 0x0002 /* prevent file from shrinking */ #define F_SEAL_GROW 0x0004 /* prevent file from growing */ #define F_SEAL_WRITE 0x0008 /* prevent writes */ +#define F_SEAL_FUTURE_WRITE 0x0010 /* prevent future writes while mapped */ /* (1U << 31) is reserved for signed error codes */ /* diff --git a/mm/memfd.c b/mm/memfd.c index 2bb5e257080e..5ba9804e9515 100644 --- a/mm/memfd.c +++ b/mm/memfd.c @@ -150,7 +150,8 @@ static unsigned int *memfd_file_seals_ptr(struct file *file) #define F_ALL_SEALS (F_SEAL_SEAL | \ F_SEAL_SHRINK | \ F_SEAL_GROW | \ - F_SEAL_WRITE) + F_SEAL_WRITE | \ + F_SEAL_FUTURE_WRITE) static int memfd_add_seals(struct file *file, unsigned int seals) { @@ -219,6 +220,25 @@ static int memfd_add_seals(struct file *file, unsigned int seals) } } + if ((seals & F_SEAL_FUTURE_WRITE) && + !(*file_seals & F_SEAL_FUTURE_WRITE)) { + /* + * The FUTURE_WRITE seal also prevents growing and shrinking + * so we need them to be already set, or requested now. + */ + int test_seals = (seals | *file_seals) & + (F_SEAL_GROW | F_SEAL_SHRINK); + + if (test_seals != (F_SEAL_GROW | F_SEAL_SHRINK)) { + error = -EINVAL; + goto unlock; + } + + spin_lock(&file->f_lock); + file->f_mode &= ~(FMODE_WRITE | FMODE_PWRITE); + spin_unlock(&file->f_lock); + } + *file_seals |= seals; error = 0;