On Wed, 2017-07-05 at 13:53 -0700, Andy Lutomirski wrote: > On Jul 5, 2017, at 12:32 PM, Ben Hutchings <b...@decadent.org.uk> wrote: > > On Wed, 2017-07-05 at 10:23 -0700, Andy Lutomirski wrote: [...] > > > - As a hardening feature, if the stack would expand within 64k or > > > whatever of a non-MAP_FIXED mapping, refuse to expand it. (This might > > > have to be a non-hinted mapping, not just a non-MAP_FIXED mapping.) > > > The idea being that, if you deliberately place a mapping under the > > > stack, you know what you're doing. If you're like LibreOffice and do > > > something daft and are thus exploitable, you're on your own. > > > - As a hardening measure, don't let mmap without MAP_FIXED position > > > something within 64k or whatever of the bottom of the stack unless a > > > MAP_FIXED mapping is between them. > > > > Having tested patches along these lines, I think the above would avoid > > the reported regressions. > > > > FWIW, even this last part may be problematic. It'll break anything > that tries to allocate many small MAP_GROWSDOWN stacks on 32- > bit. Hopefully nothing does this, but maybe Java does.
glibc (NPTL) does not. Java (at least Hotspot in OpenJDK 6,7, 8) does not. LinuxThreads *does* and is used by uclibc. dietlibc *does*. I would be surprised if either was used for applications with very many threads, but then this issue has thrown up a lot of surprises. Ben. -- Ben Hutchings Man invented language to satisfy his deep need to complain. - Lily Tomlin
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