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 06:21:42 -0800
From: Kees Cook <>
To: Bhupesh Sharma <>
Cc: "" <>, 
	"" <>, Daniel Cashman <>, 
	Michael Ellerman <>,, 
	Alexander Graf <>, Benjamin Herrenschmidt <>, 
	Paul Mackerras <>, Anatolij Gustschin <>, 
	Alistair Popple <>, Matt Porter <>, 
	Vitaly Bordug <>, Scott Wood <>, 
	Kumar Gala <>, Daniel Cashman <>
Subject: Re: [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness

On Wed, Feb 1, 2017 at 9:42 PM, Bhupesh Sharma <> 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 Cook
Pixel Security

Powered by blists - more mailing lists

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