Messages in this thread | | | Date | Tue, 25 Apr 2006 18:11:39 +0200 (CEST) | From | Axelle Apvrille <> | Subject | Re: [ANNOUNCE] Release Digsig 1.5: kernel module for run-timeauthentication of binaries |
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Hi all,
Just my few cents on signed binaries and DigSig. It's kind of a very partial reply to several parts of various emails (Arjan, Ulrich, Nix ...), sorry for that ;-)
1- "does this also prevent people writing their own elf loader in a bit of perl and just mmap the code"
I'm not sure to exactly understand what you mean:
- if you mean writing an application able to read & 'interpret' an ELF executable: again, I think DigSig will prevent this, because when you mmap the code, this calls (at kernel level) do_mmap which triggers an LSM hook called file_mmap. And we implement checks in that hook...
- if you mean modifying the ELF loader so that do_mmap / file_mmap aren't called, well you'll need to hack the kernel, won't you ?
- finally, note you also have choice not to sign this elf loader of yours. If it isn't signed, it won't ever run ;-)
2- "You will never get 100% protection from a mechanism like signed binaries"
Sure. I entirely agree though, if we're honest, *no* system is ever a 100 % protection ;-) I think our paper (http://disec.sourceforge.net/ or http://www.usenix.org/events/lisa04/tech/apvrille.html) is clear about what we mean to protect and what we do not, and IMHO, in security, we cannot expect more of any system.
3- "I've found signed binaries principally useful on stripped-down firewalls and firewall UML instances"
Indeed. I foresee use of DigSig for hosts that are not meant to change 'too' often (for example, not a developer or a user desktop - although I do personnally have DigSig on mine ;-)) ). Stripped-down servers or firewalls are good example (and they do indeed represent a big niche). BTW, I also foresee use of DigSig in small embedded systems, and actually, in that area, I heard of Umbrella, an open source project using DigSig (I don't know the status).
Hope this helps ! Best regards,
Axelle. DigSig - http://disec.sourceforge.net
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