On Tue, Nov 17, 2020 at 5:55 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > On Mon, Oct 26, 2020 at 06:05:18PM +0200, Topi Miettinen wrote: > > Writing a new value of 3 to /proc/sys/kernel/randomize_va_space > > enables full randomization of memory mappings created with mmap(NULL, > > ...). With 2, the base of the VMA used for such mappings is random, > > but the mappings are created in predictable places within the VMA and > > in sequential order. With 3, new VMAs are created to fully randomize > > the mappings. Also mremap(..., MREMAP_MAYMOVE) will move the mappings > > even if not necessary. > > Is this worth it? > > https://www.ndss-symposium.org/ndss2017/ndss-2017-programme/aslrcache-practical-cache-attacks-mmu/ Yeah, against local attacks (including from JavaScript), ASLR isn't very robust; but it should still help against true remote attacks (modulo crazyness like NetSpectre). E.g. Mateusz Jurczyk's remote Samsung phone exploit via MMS messages (https://googleprojectzero.blogspot.com/2020/08/mms-exploit-part-5-defeating-aslr-getting-rce.html) would've probably been quite a bit harder to pull off if he hadn't been able to rely on having all those memory mappings sandwiched together.
