From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id 89A636B0009 for ; Mon, 26 Mar 2018 21:57:45 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id e15so2908844wrj.14 for ; Mon, 26 Mar 2018 18:57:45 -0700 (PDT) Received: from huawei.com (lhrrgout.huawei.com. [194.213.3.17]) by mx.google.com with ESMTPS id 62si258387wml.81.2018.03.26.18.57.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Mar 2018 18:57:44 -0700 (PDT) From: Igor Stoppa Subject: [PATCH 6/6] Documentation for Pmalloc Date: Tue, 27 Mar 2018 04:55:24 +0300 Message-ID: <20180327015524.14318-7-igor.stoppa@huawei.com> In-Reply-To: <20180327015524.14318-1-igor.stoppa@huawei.com> References: <20180327015524.14318-1-igor.stoppa@huawei.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: willy@infradead.org, keescook@chromium.org, mhocko@kernel.org Cc: david@fromorbit.com, rppt@linux.vnet.ibm.com, labbott@redhat.com, linux-security-module@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, igor.stoppa@gmail.com, Igor Stoppa Detailed documentation about the protectable memory allocator. Signed-off-by: Igor Stoppa --- Documentation/core-api/index.rst | 1 + Documentation/core-api/pmalloc.rst | 101 +++++++++++++++++++++++++++++++++++++ 2 files changed, 102 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..3d2c19e5deaf --- /dev/null +++ b/Documentation/core-api/pmalloc.rst @@ -0,0 +1,101 @@ +.. 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 +------- + +The MMU available in the system can be used to write protect memory pages. +Unfortunately this feature cannot be used as-it-is, to protect sensitive +data, because it is typically interleaved with data that must stay +writeable. + +pmalloc introduces the concept of protectable memory pools. +Each pool contains a list of areas of virtually contiguous pages of +memory. An area is the minimum amount of memory that pmalloc allows to +protect, because the data it contains can be larger than a single page. + +When an allocation is performed, if there is not enough memory already +available in the pool, a new area of suitable size is allocated. +The size chosen is the largest between the roundup (to PAGE_SIZE) of +the request from pmalloc and friends and the refill parameter specified +when creating the pool. + +When a pool is created, it is possible to specify two parameters: +- refill size: the minimum size of the memory area to allocate when needed +- align_order: the default alignment to use when returning to pmalloc + +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. + +- Whatever memory was still available in the previous area (where + applicable) is relinquished. + +- Freeing of memory is not supported. Pages will be returned to the + system upon destruction of the memory pool. + +- 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 + +#. write-protect the memory so far allocated + + :c::func:`pmalloc_protect_pool` + +#. iterate over the last 3 points as needed + +#. [optional] destroy the pool + + :c:func:`pmalloc_destroy_pool` + +API +--- + +.. kernel-doc:: include/linux/pmalloc.h +.. kernel-doc:: mm/pmalloc.c -- 2.14.1