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Date: Thu, 4 Jul 2013 21:40:57 +0300
From: Timo Teras <timo.teras@iki.fi>
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Subject: Re: [Qemu-devel] [RFC PATCH] elfload: load PIE executables to right
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To: Timo =?UTF-8?Q?Ter=C3=A4s?= <timo.teras@iki.fi>
Cc: qemu-devel@nongnu.org

On Thu,  4 Jul 2013 16:01:23 +0300
Timo Ter=C3=A4s <timo.teras@iki.fi> wrote:

> PIE images are ET_DYN images. Check first for pinterp_name to make
> sure the main executable always is loaded to correct place.
>=20
> See below for current behaviour of PIE executables:
>=20
> Reserved 0x7f000000 bytes of guest address space
> host mmap_min_addr=3D0x1000
> guest_base  0x7f7cb41d5000
> start    end      size     prot
> 0037f400-003fe400 0007f000 r-x
> 003fe400-003ff400 00001000 ---
> 003ff400-003fe400 fffff000 rw-
> 003fe400-003ff400 00001000 ---
> 003ff400-003ffc00 00000800 rw-
> 003ffc00-003fec00 fffff000 r-x
> 003fec00-003ffc00 00001000 ---
> 003ffc00-0007f000 ffc7f400 rw-
> start_brk   0x00000000
> end_code    0x7eff7ac0
> start_code  0x7eff7000
> start_data  0x7efffac0
> end_data    0x7efffc18
> start_stack 0x7eff6dc8
> brk         0x7efffc34
> entry       0x7e799b30
> 00000000-00005000 ---p 00000000 00:00 0
> 00005000-00015000 rw-p 00000000 00:00 0
> 00015000-7e77d000 ---p 00000000 00:00 0
> 7e77d000-7e7ec000 r-xp 00000000 68:03 14326298          /lib/libc.so
> 7e7ec000-7e7f3000 ---p 00000000 00:00 0
> 7e7f3000-7e7f4000 rw-p 0006e000 68:03 14326298          /lib/libc.so
> 7e7f4000-7e7f6000 rw-p 00000000 00:00 0
> 7e7f6000-7e7f7000 ---p 00000000 00:00 0
> 7e7f7000-7eff7000 rw-p 00000000 00:00 0
> 7eff7000-7eff8000 r-xp 00000000 68:03 9731305          /usr/bin/brk
> 7eff8000-7efff000 ---p 00000000 00:00 0
> 7e7f7000-7eff7000 rw-p 00000000 00:00 0          [stack]
>=20
> Showing how the main binary got loaded to wrong place.

Forgot to mention. Due to the above, the brk is set wrong, and the
application will be unable to allocate any memory. Making them
practically unusable.

I've done quick testing that with this patch applied, the
PIE executables will have working brk().

- Timo