[FD] Linux ASLR mmap weakness: Reducing entropy by half

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://ift.tt/1BltFsc

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