From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753306AbbBJRZs (ORCPT ); Tue, 10 Feb 2015 12:25:48 -0500 Received: from mail-ob0-f180.google.com ([209.85.214.180]:39618 "EHLO mail-ob0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752971AbbBJRZp (ORCPT ); Tue, 10 Feb 2015 12:25:45 -0500 MIME-Version: 1.0 In-Reply-To: References: Date: Tue, 10 Feb 2015 09:25:45 -0800 X-Google-Sender-Auth: 1eGccyXYUMHwQYiYWbxBLJinZw0 Message-ID: Subject: Re: [PATCH] x86, kaslr: propagate base load address calculation From: Kees Cook To: Jiri Kosina Cc: "H. Peter Anvin" , LKML , live-patching@vger.kernel.org, Linux-MM , "x86@kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 10, 2015 at 5:17 AM, Jiri Kosina wrote: > Commit e2b32e678 ("x86, kaslr: randomize module base load address") makes > the base address for module to be unconditionally randomized in case when > CONFIG_RANDOMIZE_BASE is defined and "nokaslr" option isn't present on the > commandline. > > This is not consistent with how choose_kernel_location() decides whether > it will randomize kernel load base. > > Namely, CONFIG_HIBERNATION disables kASLR (unless "kaslr" option is > explicitly specified on kernel commandline), which makes the state space > larger than what module loader is looking at. IOW CONFIG_HIBERNATION && > CONFIG_RANDOMIZE_BASE is a valid config option, kASLR wouldn't be applied > by default in that case, but module loader is not aware of that. > > Instead of fixing the logic in module.c, this patch takes more generic > aproach, and exposes __KERNEL_OFFSET macro, which calculates the real > offset that has been established by choose_kernel_location() during boot. > This can be used later by other kernel code as well (such as, but not > limited to, live patching). > > OOPS offset dumper and module loader are converted to that they make use > of this macro as well. > > Signed-off-by: Jiri Kosina Ah, yes! This is a good clean up. Thanks! I do see, however, one corner case remaining: kASLR randomized to 0 offset. This will force module ASLR off, which I think is a mistake. Perhaps we need to export the kaslr state as a separate item to be checked directly, instead of using __KERNEL_OFFSET? -Kees > --- > arch/x86/include/asm/page_types.h | 4 ++++ > arch/x86/kernel/module.c | 10 +--------- > arch/x86/kernel/setup.c | 4 ++-- > 3 files changed, 7 insertions(+), 11 deletions(-) > > diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h > index f97fbe3..7f18eaf 100644 > --- a/arch/x86/include/asm/page_types.h > +++ b/arch/x86/include/asm/page_types.h > @@ -46,6 +46,10 @@ > > #ifndef __ASSEMBLY__ > > +/* Return kASLR relocation offset */ > +extern char _text[]; > +#define __KERNEL_OFFSET ((unsigned long)&_text - __START_KERNEL) > + > extern int devmem_is_allowed(unsigned long pagenr); > > extern unsigned long max_low_pfn_mapped; > diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c > index e69f988..d236bd2 100644 > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -46,21 +46,13 @@ do { \ > > #ifdef CONFIG_RANDOMIZE_BASE > static unsigned long module_load_offset; > -static int randomize_modules = 1; > > /* Mutex protects the module_load_offset. */ > static DEFINE_MUTEX(module_kaslr_mutex); > > -static int __init parse_nokaslr(char *p) > -{ > - randomize_modules = 0; > - return 0; > -} > -early_param("nokaslr", parse_nokaslr); > - > static unsigned long int get_module_load_offset(void) > { > - if (randomize_modules) { > + if (__KERNEL_OFFSET) { > mutex_lock(&module_kaslr_mutex); > /* > * Calculate the module_load_offset the first time this > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index c4648ada..08124a1 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -833,8 +833,8 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p) > { > pr_emerg("Kernel Offset: 0x%lx from 0x%lx " > "(relocation range: 0x%lx-0x%lx)\n", > - (unsigned long)&_text - __START_KERNEL, __START_KERNEL, > - __START_KERNEL_map, MODULES_VADDR-1); > + __KERNEL_OFFSET, __START_KERNEL, __START_KERNEL_map, > + MODULES_VADDR-1); > > return 0; > } > > -- > Jiri Kosina > SUSE Labs -- Kees Cook Chrome OS Security From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f180.google.com (mail-ob0-f180.google.com [209.85.214.180]) by kanga.kvack.org (Postfix) with ESMTP id D7F666B0032 for ; Tue, 10 Feb 2015 12:25:46 -0500 (EST) Received: by mail-ob0-f180.google.com with SMTP id vb8so33204260obc.11 for ; Tue, 10 Feb 2015 09:25:46 -0800 (PST) Received: from mail-oi0-x22d.google.com (mail-oi0-x22d.google.com. [2607:f8b0:4003:c06::22d]) by mx.google.com with ESMTPS id o185si7869468oif.15.2015.02.10.09.25.45 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 10 Feb 2015 09:25:46 -0800 (PST) Received: by mail-oi0-f45.google.com with SMTP id i138so11195130oig.4 for ; Tue, 10 Feb 2015 09:25:45 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: Date: Tue, 10 Feb 2015 09:25:45 -0800 Message-ID: Subject: Re: [PATCH] x86, kaslr: propagate base load address calculation From: Kees Cook Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Jiri Kosina Cc: "H. Peter Anvin" , LKML , live-patching@vger.kernel.org, Linux-MM , "x86@kernel.org" On Tue, Feb 10, 2015 at 5:17 AM, Jiri Kosina wrote: > Commit e2b32e678 ("x86, kaslr: randomize module base load address") makes > the base address for module to be unconditionally randomized in case when > CONFIG_RANDOMIZE_BASE is defined and "nokaslr" option isn't present on the > commandline. > > This is not consistent with how choose_kernel_location() decides whether > it will randomize kernel load base. > > Namely, CONFIG_HIBERNATION disables kASLR (unless "kaslr" option is > explicitly specified on kernel commandline), which makes the state space > larger than what module loader is looking at. IOW CONFIG_HIBERNATION && > CONFIG_RANDOMIZE_BASE is a valid config option, kASLR wouldn't be applied > by default in that case, but module loader is not aware of that. > > Instead of fixing the logic in module.c, this patch takes more generic > aproach, and exposes __KERNEL_OFFSET macro, which calculates the real > offset that has been established by choose_kernel_location() during boot. > This can be used later by other kernel code as well (such as, but not > limited to, live patching). > > OOPS offset dumper and module loader are converted to that they make use > of this macro as well. > > Signed-off-by: Jiri Kosina Ah, yes! This is a good clean up. Thanks! I do see, however, one corner case remaining: kASLR randomized to 0 offset. This will force module ASLR off, which I think is a mistake. Perhaps we need to export the kaslr state as a separate item to be checked directly, instead of using __KERNEL_OFFSET? -Kees > --- > arch/x86/include/asm/page_types.h | 4 ++++ > arch/x86/kernel/module.c | 10 +--------- > arch/x86/kernel/setup.c | 4 ++-- > 3 files changed, 7 insertions(+), 11 deletions(-) > > diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h > index f97fbe3..7f18eaf 100644 > --- a/arch/x86/include/asm/page_types.h > +++ b/arch/x86/include/asm/page_types.h > @@ -46,6 +46,10 @@ > > #ifndef __ASSEMBLY__ > > +/* Return kASLR relocation offset */ > +extern char _text[]; > +#define __KERNEL_OFFSET ((unsigned long)&_text - __START_KERNEL) > + > extern int devmem_is_allowed(unsigned long pagenr); > > extern unsigned long max_low_pfn_mapped; > diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c > index e69f988..d236bd2 100644 > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -46,21 +46,13 @@ do { \ > > #ifdef CONFIG_RANDOMIZE_BASE > static unsigned long module_load_offset; > -static int randomize_modules = 1; > > /* Mutex protects the module_load_offset. */ > static DEFINE_MUTEX(module_kaslr_mutex); > > -static int __init parse_nokaslr(char *p) > -{ > - randomize_modules = 0; > - return 0; > -} > -early_param("nokaslr", parse_nokaslr); > - > static unsigned long int get_module_load_offset(void) > { > - if (randomize_modules) { > + if (__KERNEL_OFFSET) { > mutex_lock(&module_kaslr_mutex); > /* > * Calculate the module_load_offset the first time this > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index c4648ada..08124a1 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -833,8 +833,8 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p) > { > pr_emerg("Kernel Offset: 0x%lx from 0x%lx " > "(relocation range: 0x%lx-0x%lx)\n", > - (unsigned long)&_text - __START_KERNEL, __START_KERNEL, > - __START_KERNEL_map, MODULES_VADDR-1); > + __KERNEL_OFFSET, __START_KERNEL, __START_KERNEL_map, > + MODULES_VADDR-1); > > return 0; > } > > -- > Jiri Kosina > SUSE Labs -- Kees Cook Chrome OS Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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