From: dcashman@android•com (Daniel Cashman)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR.
Date: Wed, 25 Nov 2015 11:16:46 -0800 [thread overview]
Message-ID: <5656091E.6080803@android.com> (raw)
In-Reply-To: <CAGXu5jKaW=H1WWuW_M4LpfcGGUWE3yvsiMnzMiAbeta__YpSJg@mail.gmail.com>
On 11/24/2015 04:47 PM, Kees Cook wrote:
> On Tue, Nov 24, 2015 at 4:40 PM, Andrew Morton
> <akpm@linux-foundation•org> wrote:
>> On Wed, 18 Nov 2015 15:20:05 -0800 Daniel Cashman <dcashman@android•com> wrote:
>>
>>> --- a/kernel/sysctl.c
>>> +++ b/kernel/sysctl.c
>>> @@ -1568,6 +1568,28 @@ static struct ctl_table vm_table[] = {
>>> .mode = 0644,
>>> .proc_handler = proc_doulongvec_minmax,
>>> },
>>> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
>>> + {
>>> + .procname = "mmap_rnd_bits",
>>> + .data = &mmap_rnd_bits,
>>> + .maxlen = sizeof(mmap_rnd_bits),
>>> + .mode = 0644,
>>
>> Is there any harm in permitting the attacker to read these values?
>>
>> And is there any benefit in permitting non-attackers to read them?
>
> I'm on the fence. Things like kernel/randomize_va_space is 644. But
> since I don't see a benefit in exposing them, let's make them all 600
> instead -- it's a new interface, better to keep it narrower now.
Is there any harm in allowing the attacker to read these values? Nothing
immediately comes to mind. It is a form of information leakage, and I
guess a local attacker could use this information to calibrate an attack
or decide whether or not brute-forcing is a worthy approach, but this
easily could be leaked in other ways as well.
Is there a benefit to allowing non-attackers to read them? Possibly
could be used in tests seeking to verify the system environment, but
again, this could be discovered in other ways.
I like Kees' suggestion of starting narrow and granting if need arises.
>>>
>>> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
>>> +int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
>>> +int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
>>> +int mmap_rnd_bits = CONFIG_ARCH_MMAP_RND_BITS;
>>> +#endif
>>> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
>>> +int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
>>> +int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
>>> +int mmap_rnd_compat_bits = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
>>
>> These could be __read_mostly.
>>
>> If one believes in such things. One effect of __read_mostly is to
>> clump the write-often stuff into the same cachelines and I've never
>> been convinced that one outweighs the other...
>
> The _min and _max values should be const, actually, since they're
> build-time selected. The _bits could easily be __read_mostly, yeah.
Yes, one would generally expect these to never be touched, and even if
they were, the threshold of __read_mostly would certainly be crossed.
-Dan
next prev parent reply other threads:[~2015-11-25 19:16 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-18 23:20 [PATCH v3 0/4] Allow customizable random offset to mmap_base address Daniel Cashman
2015-11-18 23:20 ` [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR Daniel Cashman
2015-11-18 23:20 ` [PATCH v3 2/4] arm: mm: support ARCH_MMAP_RND_BITS Daniel Cashman
2015-11-18 23:20 ` [PATCH v3 3/4] arm64: " Daniel Cashman
2015-11-18 23:20 ` [PATCH v3 4/4] x86: " Daniel Cashman
2015-11-19 0:16 ` Daniel Cashman
2015-11-23 15:04 ` [PATCH v3 3/4] arm64: " Will Deacon
2015-11-23 18:55 ` Daniel Cashman
2015-11-25 4:26 ` Michael Ellerman
2015-11-25 19:32 ` Daniel Cashman
2015-11-25 12:06 ` Catalin Marinas
2015-11-25 20:39 ` Daniel Cashman
2015-11-27 8:36 ` Andrey Ryabinin
2015-11-27 9:32 ` Catalin Marinas
2015-11-19 0:14 ` [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR Daniel Cashman
2015-11-25 0:40 ` Andrew Morton
2015-11-25 0:47 ` Kees Cook
2015-11-25 19:16 ` Daniel Cashman [this message]
2015-11-25 4:40 ` Michael Ellerman
2015-11-25 19:36 ` Daniel Cashman
2015-11-25 0:39 ` [PATCH v3 0/4] Allow customizable random offset to mmap_base address Andrew Morton
2015-11-25 19:07 ` Daniel Cashman
2015-11-26 15:11 ` Martin Schwidefsky
2015-11-26 7:07 ` Michael Ellerman
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