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Date: Tue, 09 Dec 2014 03:38:32 -0500
From: Daniel Micay <danielmicay@...il.com>
To: oss-security@...ts.openwall.com
Subject: Re: PIE bypass using VDSO ASLR weakness
On 09/12/14 03:05 AM, Reno Robert wrote:
> Even in 64 bit addressing, randomization of VDSO seems to be low and the
> base address could be bruteforced, thus allowing to use gadgets from VDSO
> if not from executable. Though VDSO is not rich in gadgets, it has few good
> ones to make interesting syscalls including execve(). The below blog post
> describes the availability of gadgets and feasibility of bruteforce, which
> could be combined for an effective payload.
>
> http://v0ids3curity.blogspot.in/2014/12/return-to-vdso-using-elf-auxiliary.html
>
>
> renorobert@...ntu:~$ readelf -h ./pie
> ELF Header:
> Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
> Class: ELF64
> Data: 2's complement, little endian
> Version: 1 (current)
> OS/ABI: UNIX - System V
> ABI Version: 0
> Type: DYN (Shared object file)
> Machine: Advanced Micro Devices X86-64
> Version: 0x1
> Entry point address: 0x620
>
> renorobert@...ntu:~$ while true; do ldd ./pie; done | grep
> 0x00007fff969fe000
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
> linux-vdso.so.1 => (0x00007fff969fe000)
>
> Do we need better ASLR for VDSO to make PIE more effective?
You must have COMPAT_VDSO enabled. It's randomized fine with a sane
kernel configuration.
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