linux-kernel - Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <22528348-DB08-44E2-B6C5-C4A1F50B8EF6@zytor.com>
Date:	Mon, 08 Aug 2016 21:14:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...e.de>, Thomas Garnier <thgarnie@...gle.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
	Dave Young <dyoung@...hat.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Lv Zheng <lv.zheng@...el.com>, Baoquan He <bhe@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Mark Salter <msalter@...hat.com>,
	Aleksey Makarov <aleksey.makarov@...aro.org>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Fabian Frederick <fabf@...net.be>,
	Toshi Kani <toshi.kani@...com>,
	Dan Williams <dan.j.williams@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization

On August 8, 2016 9:01:42 PM PDT, Borislav Petkov <bp@...e.de> wrote:
>On Mon, Aug 08, 2016 at 11:40:07AM -0700, Thomas Garnier wrote:
>> Default implementation expects 6 pages maximum are needed for low
>page
>> allocations. If KASLR memory randomization is enabled, the worse case
>> of e820 layout would require 12 pages (no large pages). It is due to
>the
>> PUD level randomization and the variable e820 memory layout.
>
>Can't this number of required pages be computed based on the
>randomization offset or somesuch instead of maxing it out by default on
>every machine which enables CONFIG_RANDOMIZE_MEMORY?
>
>> This bug was found while doing extensive testing of KASLR memory
>> randomization on different type of hardware.
>> 
>> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
>> ---
>> Based on next-20160805
>> ---
>>  arch/x86/mm/init.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>> 
>> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>> index 6209289..3a27e6a 100644
>> --- a/arch/x86/mm/init.c
>> +++ b/arch/x86/mm/init.c
>> @@ -130,6 +130,14 @@ void  __init early_alloc_pgt_buf(void)
>>  	unsigned long tables = INIT_PGT_BUF_SIZE;
>>  	phys_addr_t base;
>>  
>> +	/*
>> +	 * Depending on the machine e860 memory layout and the PUD
>alignement.
>
>				    e820			   alignment
>
>> +	 * We may need twice more pages when KASLR memoy randomization is
>
>						  memory
>
>> +	 * enabled.
>> +	 */
>> +	if (IS_ENABLED(CONFIG_RANDOMIZE_MEMORY))
>> +		tables *= 2;
>> +
>>  	base = __pa(extend_brk(tables, PAGE_SIZE));
>>  
>>  	pgt_buf_start = base >> PAGE_SHIFT;
>> -- 
>> 2.8.0.rc3.226.g39d4020
>> 

Upping the brk by a few pages is not a big deal.  Unused brk gets reclaimed at init release time.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.