Linux ASLR mmap weakness: Reducing entropy by half

[Hector Marco-Gisbert <hecmargi@xxxxxx>]

A bug in Linux ASLR implementation has been found. The issue is that the mmap 
base address for processes is not properly randomized on some architectures due 
to an improper bit-mask manipulation. Affected systems have reduced the mmap 
area entropy of the processes by half.

The number of possible locations are reduced by 50%, which for example will 
reduce the cost of brute force attacks.

PowerPC, Sparc64 and ARM have 18 bits of entropy. Non-vulnerable systems have 
262144 (2^18) different places to locate the mmap area. On vulnerable systems, 
this value is reduced to 131072 (2^17).


Advisory details at:
http://hmarco.org/bugs/linux-ASLR-reducing-mmap-by-half.html


--
Hector Marco-Gisbert @ http://hmarco.org/
Cyber Security Researcher @ http://cybersecurity.upv.es
Universitat Politècnica de València (Spain)