Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Tue, 3 Nov 2015 10:10:03 -0800 Daniel Cashman <dcashman@xxxxxxxxxxx> wrote: > >> ASLR currently only uses 8 bits to generate the random offset for the >> mmap base address on 32 bit architectures. This value was chosen to >> prevent a poorly chosen value from dividing the address space in such >> a way as to prevent large allocations. This may not be an issue on all >> platforms. Allow the specification of a minimum number of bits so that >> platforms desiring greater ASLR protection may determine where to place >> the trade-off. > > Can we please include a very good description of the motivation for this > change? What is inadequate about the current code, what value does the > enhancement have to our users, what real-world problems are being solved, > etc. > > Because all we have at present is "greater ASLR protection", which doesn't > really tell anyone anything. The description seemed clear to me. More random bits, more entropy, more work needed to brute force. 8 bits only requires 256 tries (or a 1 in 256) chance to brute force something. We have seen in the last couple of months on Android how only having 8 bits doesn't help much. Each additional bit doubles the protection (and unfortunately also increases fragmentation of the userspace address space). Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>