svn commit: r320430 - head/sys/vm
Shawn Webb
shawn.webb at hardenedbsd.org
Thu Jun 29 13:23:36 UTC 2017
On Wed, Jun 28, 2017 at 06:32:38PM -0400, Shawn Webb wrote:
> On Wed, Jun 28, 2017 at 04:02:37AM +0000, Konstantin Belousov wrote:
> > Author: kib
> > Date: Wed Jun 28 04:02:36 2017
> > New Revision: 320430
> > URL: https://svnweb.freebsd.org/changeset/base/320430
> >
> > Log:
> > Treat the addr argument for mmap(2) request without MAP_FIXED flag as
> > a hint.
> >
> > Right now, for non-fixed mmap(2) calls, addr is de-facto interpreted
> > as the absolute minimal address of the range where the mapping is
> > created. The VA allocator only allocates in the range [addr,
> > VM_MAXUSER_ADDRESS]. This is too restrictive, the mmap(2) call might
> > unduly fail if there is no free addresses above addr but a lot of
> > usable space below it.
> >
> > Lift this implementation limitation by allocating VA in two passes.
> > First, try to allocate above addr, as before. If that fails, do the
> > second pass with less restrictive constraints for the start of
> > allocation by specifying minimal allocation address at the max bss
> > end, if this limit is less than addr.
> >
> > One important case where this change makes a difference is the
> > allocation of the stacks for new threads in libthr. Under some
> > configuration conditions, libthr tries to hint kernel to reuse the
> > main thread stack grow area for the new stacks. This cannot work by
> > design now after grow area is converted to stack, and there is no
> > unallocated VA above the main stack. Interpreting requested stack
> > base address as the hint provides compatibility with old libthr and
> > with (mis-)configured current libthr.
> >
> > Reviewed by: alc
> > Tested by: dim (previous version)
> > Sponsored by: The FreeBSD Foundation
> > MFC after: 1 week
> >
> > Modified:
> > head/sys/vm/vm_map.c
> > head/sys/vm/vm_map.h
> > head/sys/vm/vm_mmap.c
>
> Hey Kostik,
>
> This commit breaks both xorg and shutting down/rebooting. Reverting this
> commit makes my laptop happy again.
Thnking out loud: would these issues arise due to HardenedBSD using
SafeStack, which relies on libthr's stack code?
Thanks,
--
Shawn Webb
Cofounder and Security Engineer
HardenedBSD
GPG Key ID: 0x6A84658F52456EEE
GPG Key Fingerprint: 2ABA B6BD EF6A F486 BE89 3D9E 6A84 658F 5245 6EEE
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