oss-security - Re: PIE bypass using VDSO ASLR weakness

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Date: Tue, 9 Dec 2014 20:38:08 +0100
From: Mathias Krause <minipli@...glemail.com>
To: oss-security@...ts.openwall.com
Subject: Re: PIE bypass using VDSO ASLR weakness

On 9 December 2014 at 16:33, Reno Robert <renorobert@...il.com> wrote:
> Hi Daniel, COMPAT_VDSO is not enabled. Just that randomization is 20 bits
> and same values are generated on repeated execution.
>
> On Tue, Dec 9, 2014 at 2:08 PM, Daniel Micay <danielmicay@...il.com> wrote:
>> On 09/12/14 03:05 AM, Reno Robert wrote:
>> > 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.
>>

minipli@jig:~/tmp$ echo 'int main(){}' | gcc -pie -std=c99 -xc - -o pie
minipli@jig:~/tmp$ for i in $(seq 10000); do ldd ./pie; done | grep
vdso | sort | uniq  | wc -l
10000
minipli@jig:~/tmp$ uname -rm
3.17.3-grsec+ x86_64

So Daniel's advice seems legit to me. However, sane in this context
would mean CONFIG_PAX_RANDMMAP=y ;)


Regards,
Mathias

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