From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933774AbbGGUbP (ORCPT ); Tue, 7 Jul 2015 16:31:15 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:16573 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757802AbbGGUUx (ORCPT ); Tue, 7 Jul 2015 16:20:53 -0400 From: Yinghai Lu To: Kees Cook , "H. Peter Anvin" , Baoquan He Cc: linux-kernel@vger.kernel.org Subject: [PATCH 15/42] x86, kaslr: Introduce fetch_random_virt_offset to randomize the kernel text mapping address Date: Tue, 7 Jul 2015 13:20:01 -0700 Message-Id: <1436300428-21163-16-git-send-email-yinghai@kernel.org> X-Mailer: git-send-email 1.8.4.5 In-Reply-To: <1436300428-21163-1-git-send-email-yinghai@kernel.org> References: <1436300428-21163-1-git-send-email-yinghai@kernel.org> X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Baoquan He 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 | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c index 81070e9..775c6f9 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -366,6 +366,27 @@ 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; +} + unsigned char *choose_kernel_location(unsigned char *input, unsigned long input_size, unsigned char *output, -- 1.8.4.5