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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 B0CA9C433E0 for ; Thu, 21 May 2020 01:51:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B53520709 for ; Thu, 21 May 2020 01:51:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727017AbgEUBvh (ORCPT ); Wed, 20 May 2020 21:51:37 -0400 Received: from mga03.intel.com ([134.134.136.65]:44934 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726852AbgEUBvh (ORCPT ); Wed, 20 May 2020 21:51:37 -0400 IronPort-SDR: Vux4PwE2hOHrki0kiwCHtWa6kUGUmnFTh3YjQwiwun1UKdfsYMuh0OmRQofl/JwTFhZGJv+y4b IAXGFblgLx4A== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2020 18:51:36 -0700 IronPort-SDR: vpinWiTDBl9e0kcfmS3EtFiTOd8ChqrLOikNp6Vz2fmHjI906iKosa8nVZx6J3Kd+8PfDzK2c6 rnwrE2SKsC3g== X-IronPort-AV: E=Sophos;i="5.73,416,1583222400"; d="scan'208";a="440262985" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.16]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2020 18:51:36 -0700 Subject: [PATCH v3] /dev/mem: Revoke mappings when a driver claims the region From: Dan Williams To: gregkh@linuxfoundation.org Cc: Arnd Bergmann , Ingo Molnar , Kees Cook , Matthew Wilcox , Russell King , Andrew Morton , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Date: Wed, 20 May 2020 18:35:25 -0700 Message-ID: <159002475918.686697.11844615159862491335.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-3-g996c MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Close the hole of holding a mapping over kernel driver takeover event of a given address range. Commit 90a545e98126 ("restrict /dev/mem to idle io memory ranges") introduced CONFIG_IO_STRICT_DEVMEM with the goal of protecting the kernel against scenarios where a /dev/mem user tramples memory that a kernel driver owns. However, this protection only prevents *new* read(), write() and mmap() requests. Established mappings prior to the driver calling request_mem_region() are left alone. Especially with persistent memory, and the core kernel metadata that is stored there, there are plentiful scenarios for a /dev/mem user to violate the expectations of the driver and cause amplified damage. Teach request_mem_region() to find and shoot down active /dev/mem mappings that it believes it has successfully claimed for the exclusive use of the driver. Effectively a driver call to request_mem_region() becomes a hole-punch on the /dev/mem device. The typical usage of unmap_mapping_range() is part of truncate_pagecache() to punch a hole in a file, but in this case the implementation is only doing the "first half" of a hole punch. Namely it is just evacuating current established mappings of the "hole", and it relies on the fact that /dev/mem establishes mappings in terms of absolute physical address offsets. Once existing mmap users are invalidated they can attempt to re-establish the mapping, or attempt to continue issuing read(2) / write(2) to the invalidated extent, but they will then be subject to the CONFIG_IO_STRICT_DEVMEM checking that can block those subsequent accesses. Cc: Arnd Bergmann Cc: Ingo Molnar Cc: Kees Cook Cc: Matthew Wilcox Cc: Russell King Cc: Andrew Morton Cc: Greg Kroah-Hartman Fixes: 90a545e98126 ("restrict /dev/mem to idle io memory ranges") Signed-off-by: Dan Williams --- Changes since v2 [1]: - Fix smp_wmb() placement relative to publishing write (Matthew) [1]: http://lore.kernel.org/r/158987153989.4000084.17143582803685077783.stgit@dwillia2-desk3.amr.corp.intel.com drivers/char/mem.c | 104 +++++++++++++++++++++++++++++++++++++++++++- include/linux/ioport.h | 6 +++ include/uapi/linux/magic.h | 1 kernel/resource.c | 5 ++ 4 files changed, 114 insertions(+), 2 deletions(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 43dd0891ca1e..46bea7a25983 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -31,11 +31,15 @@ #include #include #include +#include +#include +#include #ifdef CONFIG_IA64 # include #endif +#define DEVMEM_MINOR 1 #define DEVPORT_MINOR 4 static inline unsigned long size_inside_page(unsigned long start, @@ -805,12 +809,66 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig) return ret; } +static struct inode *devmem_inode; + +#ifdef CONFIG_IO_STRICT_DEVMEM +void revoke_devmem(struct resource *res) +{ + struct inode *inode = READ_ONCE(devmem_inode); + + /* + * Check that the initialization has completed. Losing the race + * is ok because it means drivers are claiming resources before + * the fs_initcall level of init and prevent /dev/mem from + * establishing mappings. + */ + smp_rmb(); + if (!inode) + return; + + /* + * The expectation is that the driver has successfully marked + * the resource busy by this point, so devmem_is_allowed() + * should start returning false, however for performance this + * does not iterate the entire resource range. + */ + if (devmem_is_allowed(PHYS_PFN(res->start)) && + devmem_is_allowed(PHYS_PFN(res->end))) { + /* + * *cringe* iomem=relaxed says "go ahead, what's the + * worst that can happen?" + */ + return; + } + + unmap_mapping_range(inode->i_mapping, res->start, resource_size(res), 1); +} +#endif + static int open_port(struct inode *inode, struct file *filp) { + int rc; + if (!capable(CAP_SYS_RAWIO)) return -EPERM; - return security_locked_down(LOCKDOWN_DEV_MEM); + rc = security_locked_down(LOCKDOWN_DEV_MEM); + if (rc) + return rc; + + if (iminor(inode) != DEVMEM_MINOR) + return 0; + + /* + * Use a unified address space to have a single point to manage + * revocations when drivers want to take over a /dev/mem mapped + * range. + */ + inode->i_mapping = devmem_inode->i_mapping; + inode->i_mapping->host = devmem_inode; + filp->f_mapping = inode->i_mapping; + + return 0; } #define zero_lseek null_lseek @@ -885,7 +943,7 @@ static const struct memdev { fmode_t fmode; } devlist[] = { #ifdef CONFIG_DEVMEM - [1] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET }, + [DEVMEM_MINOR] = { "mem", 0, &mem_fops, FMODE_UNSIGNED_OFFSET }, #endif #ifdef CONFIG_DEVKMEM [2] = { "kmem", 0, &kmem_fops, FMODE_UNSIGNED_OFFSET }, @@ -939,6 +997,46 @@ static char *mem_devnode(struct device *dev, umode_t *mode) static struct class *mem_class; +static int devmem_fs_init_fs_context(struct fs_context *fc) +{ + return init_pseudo(fc, DEVMEM_MAGIC) ? 0 : -ENOMEM; +} + +static struct file_system_type devmem_fs_type = { + .name = "devmem", + .owner = THIS_MODULE, + .init_fs_context = devmem_fs_init_fs_context, + .kill_sb = kill_anon_super, +}; + +static int devmem_init_inode(void) +{ + static struct vfsmount *devmem_vfs_mount; + static int devmem_fs_cnt; + struct inode *inode; + int rc; + + rc = simple_pin_fs(&devmem_fs_type, &devmem_vfs_mount, &devmem_fs_cnt); + if (rc < 0) { + pr_err("Cannot mount /dev/mem pseudo filesystem: %d\n", rc); + return rc; + } + + inode = alloc_anon_inode(devmem_vfs_mount->mnt_sb); + if (IS_ERR(inode)) { + rc = PTR_ERR(inode); + pr_err("Cannot allocate inode for /dev/mem: %d\n", rc); + simple_release_fs(&devmem_vfs_mount, &devmem_fs_cnt); + return rc; + } + + /* publish /dev/mem initialized */ + smp_wmb(); + WRITE_ONCE(devmem_inode, inode); + + return 0; +} + static int __init chr_dev_init(void) { int minor; @@ -960,6 +1058,8 @@ static int __init chr_dev_init(void) */ if ((minor == DEVPORT_MINOR) && !arch_has_dev_port()) continue; + if ((minor == DEVMEM_MINOR) && devmem_init_inode() != 0) + continue; device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor), NULL, devlist[minor].name); diff --git a/include/linux/ioport.h b/include/linux/ioport.h index a9b9170b5dd2..6c3eca90cbc4 100644 --- a/include/linux/ioport.h +++ b/include/linux/ioport.h @@ -301,5 +301,11 @@ struct resource *devm_request_free_mem_region(struct device *dev, struct resource *request_free_mem_region(struct resource *base, unsigned long size, const char *name); +#ifdef CONFIG_IO_STRICT_DEVMEM +void revoke_devmem(struct resource *res); +#else +static inline void revoke_devmem(struct resource *res) { }; +#endif + #endif /* __ASSEMBLY__ */ #endif /* _LINUX_IOPORT_H */ diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h index d78064007b17..f3956fc11de6 100644 --- a/include/uapi/linux/magic.h +++ b/include/uapi/linux/magic.h @@ -94,6 +94,7 @@ #define BALLOON_KVM_MAGIC 0x13661366 #define ZSMALLOC_MAGIC 0x58295829 #define DMA_BUF_MAGIC 0x444d4142 /* "DMAB" */ +#define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ #define Z3FOLD_MAGIC 0x33 #define PPC_CMM_MAGIC 0xc7571590 diff --git a/kernel/resource.c b/kernel/resource.c index 76036a41143b..841737bbda9e 100644 --- a/kernel/resource.c +++ b/kernel/resource.c @@ -1126,6 +1126,7 @@ struct resource * __request_region(struct resource *parent, { DECLARE_WAITQUEUE(wait, current); struct resource *res = alloc_resource(GFP_KERNEL); + struct resource *orig_parent = parent; if (!res) return NULL; @@ -1176,6 +1177,10 @@ struct resource * __request_region(struct resource *parent, break; } write_unlock(&resource_lock); + + if (res && orig_parent == &iomem_resource) + revoke_devmem(res); + return res; } EXPORT_SYMBOL(__request_region);