From: Topi Miettinen <toiwoton@gmail.com>
To: David Laight <David.Laight@ACULAB.COM>,
'Mike Rapoport' <rppt@kernel.org>
Cc: "linux-hardening@vger.kernel.org"
<linux-hardening@vger.kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>, Jann Horn <jannh@google.com>,
Kees Cook <keescook@chromium.org>,
Linux API <linux-api@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] mm/vmalloc: randomize vmalloc() allocations
Date: Fri, 4 Dec 2020 18:53:47 +0200 [thread overview]
Message-ID: <dd8cf1b1-112c-3045-2b4c-bc6c1a6ee382@gmail.com> (raw)
In-Reply-To: <f2f19b0c0f4148a8aaa64fd7bdc821d1@AcuMS.aculab.com>
On 4.12.2020 15.33, David Laight wrote:
> From: Topi Miettinen
>> Sent: 04 December 2020 10:58
>>
>> On 4.12.2020 1.15, David Laight wrote:
>>> From: Mike Rapoport
>>>> Sent: 03 December 2020 06:58
>>>>
>>>> On Wed, Dec 02, 2020 at 08:49:06PM +0200, Topi Miettinen wrote:
>>>>> On 1.12.2020 23.45, Topi Miettinen wrote:
>>>>>> Memory mappings inside kernel allocated with vmalloc() are in
>>>>>> predictable order and packed tightly toward the low addresses. With
>>>>>> new kernel boot parameter 'randomize_vmalloc=1', the entire area is
>>>>>> used randomly to make the allocations less predictable and harder to
>>>>>> guess for attackers.
>>>
>>> Isn't that going to horribly fragment the available address space
>>> and make even moderate sized allocation requests fail (or sleep).
>>
>> For 32 bit architecture this is a real issue, but I don't think for 64
>> bits it will be a problem. You can't fragment the virtual memory space
>> for small allocations because the resulting page tables will not fit in
>> RAM for existing or near future systems.
>
> Hmmm truly random allocations are going to need 3 or 4 extra page tables
> on 64bit systems. A bit overhead for 4k allocates.
> While you won't run out of address space, you will run out of memory.
There are 3500 entries in /proc/vmallocinfo on my system with lots of
BPF filters (which allocate 8kB blocks). The total memory used is 740MB.
Assuming that every entry needed additional 4 pages, it would mean 55MB,
or 7.4% extra. I don't think that's a problem and even if it would be in
some case, there's still the option of not using randomize_vmalloc.
-Topi
next prev parent reply other threads:[~2020-12-04 16:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 21:45 [PATCH] mm/vmalloc: randomize vmalloc() allocations Topi Miettinen
2020-12-02 18:49 ` Topi Miettinen
2020-12-03 6:58 ` Mike Rapoport
2020-12-03 23:15 ` David Laight
2020-12-04 10:58 ` Topi Miettinen
2020-12-04 13:33 ` David Laight
2020-12-04 16:53 ` Topi Miettinen [this message]
2020-12-09 19:08 ` Topi Miettinen
2020-12-10 19:58 ` Topi Miettinen
2020-12-02 18:53 ` Matthew Wilcox
2020-12-02 21:28 ` Topi Miettinen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=dd8cf1b1-112c-3045-2b4c-bc6c1a6ee382@gmail.com \
--to=toiwoton@gmail.com \
--cc=David.Laight@ACULAB.COM \
--cc=akpm@linux-foundation.org \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=rppt@kernel.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).