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From: Kees Cook <keescook@chromium.org>
To: Bhupesh Sharma <bhsharma@redhat.com>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	Daniel Cashman <dcashman@google.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	bhupesh.linux@gmail.com, Alexander Graf <agraf@suse.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Anatolij Gustschin <agust@denx.de>,
	Alistair Popple <alistair@popple.id.au>,
	Matt Porter <mporter@kernel.crashing.org>,
	Vitaly Bordug <vitb@kernel.crashing.org>,
	Scott Wood <oss@buserror.net>,
	Kumar Gala <galak@kernel.crashing.org>,
	Daniel Cashman <dcashman@android.com>
Subject: Re: [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness
Date: Thu, 2 Feb 2017 06:21:42 -0800	[thread overview]
Message-ID: <CAGXu5jKYMLU1f3bWism+V59cuAeQnm7Fc9zncamq9S8guGR6TQ@mail.gmail.com> (raw)
In-Reply-To: <1486014168-1279-1-git-send-email-bhsharma@redhat.com>

On Wed, Feb 1, 2017 at 9:42 PM, Bhupesh Sharma <bhsharma@redhat.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

-- 
Kees Cook
Pixel Security

WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Bhupesh Sharma <bhsharma@redhat.com>
Cc: "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	Daniel Cashman <dcashman@google.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	bhupesh.linux@gmail.com, Alexander Graf <agraf@suse.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Anatolij Gustschin <agust@denx.de>,
	Alistair Popple <alistair@popple.id.au>,
	Matt Porter <mporter@kernel.crashing.org>,
	Vitaly Bordug <vitb@kernel.crashing.org>,
	Scott Wood <oss@buserror.net>,
	Kumar Gala <galak@kernel.crashing.org>,
	Daniel Cashman <dcashman@android.com>
Subject: [kernel-hardening] Re: [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness
Date: Thu, 2 Feb 2017 06:21:42 -0800	[thread overview]
Message-ID: <CAGXu5jKYMLU1f3bWism+V59cuAeQnm7Fc9zncamq9S8guGR6TQ@mail.gmail.com> (raw)
In-Reply-To: <1486014168-1279-1-git-send-email-bhsharma@redhat.com>

On Wed, Feb 1, 2017 at 9:42 PM, Bhupesh Sharma <bhsharma@redhat.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

-- 
Kees Cook
Pixel Security

  parent reply	other threads:[~2017-02-02 14:21 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-02  5:42 [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness Bhupesh Sharma
2017-02-02  5:42 ` [kernel-hardening] " Bhupesh Sharma
2017-02-02  5:42 ` [PATCH 1/2] powerpc: mm: support ARCH_MMAP_RND_BITS Bhupesh Sharma
2017-02-02  5:42   ` [kernel-hardening] " Bhupesh Sharma
2017-02-02  9:11   ` Balbir Singh
2017-02-02  9:11     ` [kernel-hardening] " Balbir Singh
2017-02-02 18:14     ` Bhupesh Sharma
2017-02-02 18:14       ` [kernel-hardening] " Bhupesh Sharma
2017-02-02 10:23   ` Michael Ellerman
2017-02-02 10:23     ` [kernel-hardening] " Michael Ellerman
2017-02-02 12:22     ` Balbir Singh
2017-02-02 12:22       ` [kernel-hardening] " Balbir Singh
2017-02-02 23:59       ` Michael Ellerman
2017-02-08 12:53     ` Bhupesh Sharma
2017-02-08 12:53       ` [kernel-hardening] " Bhupesh Sharma
2017-02-10 11:01       ` Michael Ellerman
2017-02-10 11:11         ` Bhupesh Sharma
2017-02-16  4:49           ` Bhupesh Sharma
2017-02-24  7:32             ` Bhupesh Sharma
2017-02-24  9:53               ` Michael Ellerman
2017-02-24  9:53                 ` Michael Ellerman
2017-02-02 14:25   ` Kees Cook
2017-02-02 14:25     ` [kernel-hardening] " Kees Cook
2017-02-02 18:04     ` Bhupesh Sharma
2017-02-02 18:04       ` [kernel-hardening] " Bhupesh Sharma
2017-02-02  5:42 ` [PATCH 2/2] powerpc: Redefine ELF_ET_DYN_BASE Bhupesh Sharma
2017-02-02  5:42   ` [kernel-hardening] " Bhupesh Sharma
2017-02-02  6:44 ` [PATCH 0/2] RFC: Adjust powerpc ASLR elf randomness Balbir Singh
2017-02-02  6:44   ` [kernel-hardening] " Balbir Singh
2017-02-02 18:21   ` Bhupesh Sharma
2017-02-02 18:21     ` [kernel-hardening] " Bhupesh Sharma
2017-02-02 14:21 ` Kees Cook [this message]
2017-02-02 14:21   ` Kees Cook
2017-02-02 18:08   ` Bhupesh Sharma
2017-02-02 18:08     ` [kernel-hardening] " Bhupesh Sharma
2017-02-02 19:19     ` Kees Cook
2017-02-02 19:19       ` [kernel-hardening] " Kees Cook
2017-02-02 19:43       ` Bhupesh Sharma
2017-02-02 19:43         ` [kernel-hardening] " Bhupesh Sharma

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