Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756892Ab3CSOu0 (ORCPT ); Tue, 19 Mar 2013 10:50:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:13556 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756830Ab3CSOuW (ORCPT ); Tue, 19 Mar 2013 10:50:22 -0400 From: Prarit Bhargava To: linux-kernel@vger.kernel.org Cc: Prarit Bhargava , Clemens Ladisch Subject: Re: [PATCH] hpet, allow user controlled mmap for user processes Date: Tue, 19 Mar 2013 10:49:56 -0400 Message-Id: <1363704596-12276-1-git-send-email-prarit@redhat.com> In-Reply-To: <5148171D.10807@ladisch.de> References: <5148171D.10807@ladisch.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3964 Lines: 115 The CONFIG_HPET_MMAP Kconfig option exposes the memory map of the HPET registers to userspace. The Kconfig help points out that in some cases this can be a security risk as some systems may erroneously configure the map such that additional data is exposed to userspace. This is a problem for distributions -- some users want the MMAP functionality but it comes with a significant security risk. In an effort to mitigate this risk, and due to the low number of users of the MMAP functionality, I've introduced a kernel parameter, hpet_mmap_enable, that is required in order to actually have the HPET MMAP exposed. [v2]: Clemens suggested modifying the Kconfig help text and making the default setting configurable. [v3]: Fixed up Documentation and Kconfig entries, default now "Y" Signed-off-by: Prarit Bhargava Cc: Clemens Ladisch --- Documentation/kernel-parameters.txt | 4 ++++ drivers/char/Kconfig | 9 +++++++-- drivers/char/hpet.c | 21 +++++++++++++++++++-- 3 files changed, 30 insertions(+), 4 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index e567af3..1444491 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -962,6 +962,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. VIA, nVidia) verbose: show contents of HPET registers during setup + hpet_mmap= [X86, HPET_MMAP] option to expose HPET MMAP to + userspace. By default this is disabled. Values are + 0(disabled) or 1(enabled). + hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. On x86-64 and powerpc, this option can be specified diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig index 3bb6fa3..51b62a1 100644 --- a/drivers/char/Kconfig +++ b/drivers/char/Kconfig @@ -534,10 +534,15 @@ config HPET_MMAP If you say Y here, user applications will be able to mmap the HPET registers. +config HPET_MMAP_DEFAULT + bool "Enable HPET MMAP access by default" + default y + depends on HPET_MMAP + help In some hardware implementations, the page containing HPET registers may also contain other things that shouldn't be - exposed to the user. If this applies to your hardware, - say N here. + exposed to the user. This option selects the default user access + to the HPET registers for applications that require it. config HANGCHECK_TIMER tristate "Hangcheck timer" diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c index e3f9a99..0f32e30 100644 --- a/drivers/char/hpet.c +++ b/drivers/char/hpet.c @@ -367,12 +367,26 @@ static unsigned int hpet_poll(struct file *file, poll_table * wait) return 0; } +#ifdef CONFIG_HPET_MMAP +static int hpet_mmap_enabled = CONFIG_HPET_MMAP_DEFAULT; + +static __init int hpet_mmap_enable(char *str) +{ + get_option(&str, &hpet_mmap_enabled); + pr_info(KERN_INFO "HPET MMAP %s\n", + hpet_mmap_enabled ? "disabled" : "enabled"); + return 1; +} +__setup("hpet_mmap", hpet_mmap_enable); + static int hpet_mmap(struct file *file, struct vm_area_struct *vma) { -#ifdef CONFIG_HPET_MMAP struct hpet_dev *devp; unsigned long addr; + if (!hpet_mmap_enabled) + return -EACCES; + if (((vma->vm_end - vma->vm_start) != PAGE_SIZE) || vma->vm_pgoff) return -EINVAL; @@ -393,10 +407,13 @@ static int hpet_mmap(struct file *file, struct vm_area_struct *vma) } return 0; +} #else +static int hpet_mmap(struct file *file, struct vm_area_struct *vma) +{ return -ENOSYS; -#endif } +#endif static int hpet_fasync(int fd, struct file *file, int on) { -- 1.8.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/