kernel-hardening - Re: [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness

Follow @Openwall on Twitter for new release announcements and other news

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

Date: Thu, 2 Feb 2017 23:38:39 +0530
From: Bhupesh Sharma <bhsharma@...hat.com>
To: Kees Cook <keescook@...omium.org>
Cc: "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Daniel Cashman <dcashman@...gle.com>, 
	Michael Ellerman <mpe@...erman.id.au>, Bhupesh SHARMA <bhupesh.linux@...il.com>, 
	Alexander Graf <agraf@...e.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, 
	Paul Mackerras <paulus@...ba.org>, Anatolij Gustschin <agust@...x.de>, 
	Alistair Popple <alistair@...ple.id.au>, Matt Porter <mporter@...nel.crashing.org>, 
	Vitaly Bordug <vitb@...nel.crashing.org>, Scott Wood <oss@...error.net>, 
	Kumar Gala <galak@...nel.crashing.org>, Daniel Cashman <dcashman@...roid.com>
Subject: Re: [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness

Hi Kees,

Thanks for the review.
Please see my comments inline.

On Thu, Feb 2, 2017 at 7:51 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Feb 1, 2017 at 9:42 PM, Bhupesh Sharma <bhsharma@...hat.com> wrote:
>> This RFC patchset tries to make the powerpc ASLR elf randomness
>> implementation similar to other ARCHs (like x86).
>>
>> The 1st patch introduces the support of ARCH_MMAP_RND_BITS in powerpc
>> mmap implementation to allow a sane balance between increased randomness
>> in the mmap address of ASLR elfs and increased address space
>> fragmentation.
>>
>> The 2nd patch increases the ELF_ET_DYN_BASE value from the current
>> hardcoded value of 0x2000_0000 to something more practical,
>> i.e. TASK_SIZE - PAGE_SHIFT (which makes sense especially for
>> 64-bit platforms which would like to utilize more randomization
>> in the load address of a PIE elf).
>
> I don't think you want this second patch. Moving ELF_ET_DYN_BASE to
> the top of TASK_SIZE means you'll be constantly colliding with stack
> and mmap randomization. 0x20000000 is way better since it randomizes
> up from there towards the mmap area.
>
> Is there a reason to avoid the 32-bit memory range for the ELF addresses?
>
> -Kees

I think you are right. Hmm, I think I was going by my particular use
case which might not be required for generic PPC platforms.

I have one doubt though - I have primarily worked on arm64 and x86
architectures and there I see there 64-bit user space applications
using the 64-bit load addresses/ranges. I am not sure why PPC64 is
different historically.

Regards,
Bhupesh

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.