From patchwork Wed Feb 28 20:06:20 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Igor Stoppa X-Patchwork-Id: 10249587 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 68F5360211 for ; Wed, 28 Feb 2018 20:11:47 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 55D1B28B0C for ; Wed, 28 Feb 2018 20:11:47 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4AA7928DF3; Wed, 28 Feb 2018 20:11:47 +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=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham 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 D3BC028B0C for ; Wed, 28 Feb 2018 20:11:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934088AbeB1ULp (ORCPT ); Wed, 28 Feb 2018 15:11:45 -0500 Received: from lhrrgout.huawei.com ([194.213.3.17]:27900 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S934011AbeB1ULp (ORCPT ); Wed, 28 Feb 2018 15:11:45 -0500 Received: from LHREML712-CAH.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id 0093E9C11E15; Wed, 28 Feb 2018 20:11:42 +0000 (GMT) Received: from localhost.localdomain (10.122.225.51) by smtpsuk.huawei.com (10.201.108.35) with Microsoft SMTP Server (TLS) id 14.3.361.1; Wed, 28 Feb 2018 20:11:34 +0000 From: Igor Stoppa To: , , , CC: , , , , , Igor Stoppa Subject: [PATCH 7/7] Documentation for Pmalloc Date: Wed, 28 Feb 2018 22:06:20 +0200 Message-ID: <20180228200620.30026-8-igor.stoppa@huawei.com> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20180228200620.30026-1-igor.stoppa@huawei.com> References: <20180228200620.30026-1-igor.stoppa@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.122.225.51] X-CFilter-Loop: Reflected Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP Detailed documentation about the protectable memory allocator. Signed-off-by: Igor Stoppa Reviewed-by: Jay Freyensee --- Documentation/core-api/index.rst | 1 + Documentation/core-api/pmalloc.rst | 111 +++++++++++++++++++++++++++++++++++++ 2 files changed, 112 insertions(+) create mode 100644 Documentation/core-api/pmalloc.rst diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst index c670a8031786..8f5de42d6571 100644 --- a/Documentation/core-api/index.rst +++ b/Documentation/core-api/index.rst @@ -25,6 +25,7 @@ Core utilities genalloc errseq printk-formats + pmalloc Interfaces for kernel debugging =============================== diff --git a/Documentation/core-api/pmalloc.rst b/Documentation/core-api/pmalloc.rst new file mode 100644 index 000000000000..8fb9c9d3171b --- /dev/null +++ b/Documentation/core-api/pmalloc.rst @@ -0,0 +1,111 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Protectable memory allocator +============================ + +Purpose +------- + +The pmalloc library is meant to provide R/O status to data that, for some +reason, could neither be declared as constant, nor could it take advantage +of the qualifier __ro_after_init, but is write-once and read-only in spirit. +It protects data from both accidental and malicious overwrites. + +Example: A policy that is loaded from userspace. + + +Concept +------- + +pmalloc builds on top of genalloc, using the same concept of memory pools. + +The value added by pmalloc is that now the memory contained in a pool can +become R/O, for the rest of the life of the pool. + +Different kernel drivers and threads can use different pools, for finer +control of what becomes R/O and when. And for improved lockless concurrency. + + +Caveats +------- + +- Memory freed while a pool is not yet protected will be reused. + +- Once a pool is protected, it's not possible to allocate any more memory + from it. + +- Memory "freed" from a protected pool indicates that such memory is not + in use anymore by the requester; however, it will not become available + for further use, until the pool is destroyed. + +- pmalloc does not provide locking support with respect to allocating vs + protecting an individual pool, for performance reasons. + It is recommended not to share the same pool between unrelated functions. + Should sharing be a necessity, the user of the shared pool is expected + to implement locking for that pool. + +- pmalloc uses genalloc to optimize the use of the space it allocates + through vmalloc. Some more TLB entries will be used, however less than + in the case of using vmalloc directly. The exact number depends on the + size of each allocation request and possible slack. + +- Considering that not much data is supposed to be dynamically allocated + and then marked as read-only, it shouldn't be an issue that the address + range for pmalloc is limited, on 32-bit systems. + +- Regarding SMP systems, the allocations are expected to happen mostly + during an initial transient, after which there should be no more need to + perform cross-processor synchronizations of page tables. + +- To facilitate the conversion of existing code to pmalloc pools, several + helper functions are provided, mirroring their kmalloc counterparts. + + +Use +--- + +The typical sequence, when using pmalloc, is: + +1. create a pool + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pmalloc_create_pool + +2. [optional] pre-allocate some memory in the pool + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pmalloc_prealloc + +3. issue one or more allocation requests to the pool with locking as needed + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pmalloc + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pzalloc + +4. initialize the memory obtained with desired values + +5. [optional] iterate over points 3 & 4 as needed + +6. write-protect the pool + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pmalloc_protect_pool + +7. use in read-only mode the handles obtained through the allocations + +8. [optional] release all the memory allocated + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pfree + +9. [optional, but depends on point 8] destroy the pool + +.. kernel-doc:: include/linux/pmalloc.h + :functions: pmalloc_destroy_pool + +API +--- + +.. kernel-doc:: include/linux/pmalloc.h