Messages in this thread | | | Date | Fri, 29 Jun 2007 12:39:54 -0700 | From | Andy Isaacson <> | Subject | Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer madness |
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On Thu, Jun 28, 2007 at 10:57:00PM -0400, Kyle Moffett wrote: > On Jun 28, 2007, at 14:49:24, Davide Libenzi wrote: > >So I implemented a rather quick hack that introduces a new mmap() > >flag MAP_NOZERO (only valid for anonymous mappings) and the vma > >counter-part VM_NOZERO. Also, a new sys_brk2() has been introduced > >to accept a new flags parameter. A brief description of the > >patches follows in the next emails. > > Hmm, sounds like this would also need a "MAP_NOREUSE" flag of some > kind for security sensitive applications. Basically, I wouldn't want > my ssh-agent pages holding private SSH keys to be reused by my web > browser which then gets exploited :-D.
PGP at least (and I think GPG still) did overwrite keys before calling free(), and attempted to use mlock(). Looks like ssh-agent doesn't use mlock -- at least it hasn't in this case: % grep Lck /proc/`pidof ssh-agent`/status VmLck: 0 kB % ulimit -a | grep lock file size (blocks) unlimited core file size (blocks) 0 locked-in-memory size (kb) 32 file locks unlimited
Requiring security-sensitive apps to use a new flag to get safe behavior is dangerous. Better to be safe by default and turn on the less-safe-but-faster behavior for the cases that benefit from it.
> It would also be a massive > information leak under SELinux. To fix it properly according to the > SELinux model you would need to tag each page with a label > immediately after it's freed and then do an access-vector-check > against the old page and the new process before allowing reuse. On > the other hand, that would probably be at least as expensive as > zeroing the page.
I still think that using uid in mm_struct is wrong, and some kind of abstraction is required. I called this "free pool" in <20070628061911.GA16986@hexapodia.org>, but I think that name is misleading -- I am not proposing that this should be part of the management of free pages, but should be a label which abstracts "safe to share freed pages among" groups. Then different SELinux protection domains would simply have different labels.
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