From patchwork Tue Mar 13 21:45:54 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Igor Stoppa X-Patchwork-Id: 10280967 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 BFB286038F for ; Tue, 13 Mar 2018 21:52:25 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B17B128521 for ; Tue, 13 Mar 2018 21:52:25 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id A616B28538; Tue, 13 Mar 2018 21:52:25 +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=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 8AE9F28521 for ; Tue, 13 Mar 2018 21:52:24 +0000 (UTC) Received: (qmail 24356 invoked by uid 550); 13 Mar 2018 21:52:22 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 24333 invoked from network); 13 Mar 2018 21:52:21 -0000 From: Igor Stoppa To: , , , , CC: , , , , , Igor Stoppa Subject: [PATCH 8/8] Documentation for Pmalloc Date: Tue, 13 Mar 2018 23:45:54 +0200 Message-ID: <20180313214554.28521-9-igor.stoppa@huawei.com> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20180313214554.28521-1-igor.stoppa@huawei.com> References: <20180313214554.28521-1-igor.stoppa@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.122.225.51] X-CFilter-Loop: Reflected X-Virus-Scanned: ClamAV using ClamSMTP Detailed documentation about the protectable memory allocator. Signed-off-by: Igor Stoppa --- 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..10e01187d049 --- /dev/null +++ b/Documentation/core-api/pmalloc.rst @@ -0,0 +1,111 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _pmalloc: + +Protectable memory allocator +============================ + +Purpose +------- + +The pmalloc library is meant to provide read-only 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 :ref:`genalloc `, using the same +concept of memory pools. + +The value added by pmalloc is that now the memory contained in a pool can +become read-only, for the rest of the life of the pool. + +Different kernel drivers and threads can use different pools, for finer +control of what becomes read_only and when. +And for improved lockless concurrency. + + +Caveats +------- + +- To facilitate the conversion of existing code to pmalloc pools, several + helper functions are provided, mirroring their k/vmalloc counterparts. + In particular, pfree(), which is mostly meant for error paths, when one + or more previous allocations must be rolled back. + +- 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. + + +Use +--- + +The typical sequence, when using pmalloc, is: + +#. create a pool + + :c:func:`pmalloc_create_pool` + +#. [optional] pre-allocate some memory in the pool + + :c:func:`pmalloc_prealloc` + +#. issue one or more allocation requests to the pool with locking as needed + + :c:func:`pmalloc` + + :c:func:`pzalloc` + +#. initialize the memory obtained with desired values + +#. [optional] iterate over points 3 & 4 as needed + +#. write-protect the pool + + :c::func:`pmalloc_protect_pool` + +#. use in read-only mode the handles obtained through the allocations + +#. [optional] release all the memory allocated + + :c:func:`pfree` + +#. [optional, but depends on point 8] destroy the pool + :c:func:`pmalloc_destroy_pool` + +API +--- + +.. kernel-doc:: include/linux/pmalloc.h +.. kernel-doc:: mm/pmalloc.c