From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751555AbbCHGSv (ORCPT ); Sun, 8 Mar 2015 01:18:51 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52543 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751325AbbCHGSb (ORCPT ); Sun, 8 Mar 2015 01:18:31 -0500 From: Baoquan He To: keescook@chromium.org, yinghai@kernel.org, hpa@zytor.com, mingo@redhat.com, bp@suse.de, matt.fleming@intel.com, vgoyal@redhat.com, tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, Baoquan He Subject: [Patch v3 4/7] x86, kaslr: Introduce fetch_random_virt_offset to randomize the kernel text mapping address Date: Sun, 8 Mar 2015 13:38:52 +0800 Message-Id: <1425793135-2833-5-git-send-email-bhe@redhat.com> In-Reply-To: <1425793135-2833-1-git-send-email-bhe@redhat.com> References: <1425793135-2833-1-git-send-email-bhe@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kaslr extended kernel text mapping region size from 512M to 1G, namely CONFIG_RANDOMIZE_BASE_MAX_OFFSET. This means kernel text can be mapped to below region: [__START_KERNEL_map + LOAD_PHYSICAL_ADDR, __START_KERNEL_map + 1G] Introduce a function find_random_virt_offset() to get random value between LOAD_PHYSICAL_ADDR and CONFIG_RANDOMIZE_BASE_MAX_OFFSET. This random value will be added to __START_KERNEL_map to get the starting address which kernel text is mapped from. Since slot can be anywhere of this region, means it is an independent slot_area, it is simple to get a slot according to random value. Signed-off-by: Baoquan He --- arch/x86/boot/compressed/aslr.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c index afb1641..0ca4c5b 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -382,6 +382,28 @@ static unsigned long find_random_addr(unsigned long minimum, return slots_fetch_random(); } +static unsigned long find_random_virt_offset(unsigned long minimum, + unsigned long image_size) +{ + unsigned long slot_num, random; + + /* Make sure minimum is aligned. */ + minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); + + if (image_size <= CONFIG_PHYSICAL_ALIGN) + slot_num = (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - minimum) / + CONFIG_PHYSICAL_ALIGN; + else + slot_num = (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - + minimum - image_size) / + CONFIG_PHYSICAL_ALIGN + 1; + + random = get_random_long() % slot_num; + + return random * CONFIG_PHYSICAL_ALIGN + minimum; +} + + static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled) { struct setup_data *data; -- 1.9.3