Use Linux only for playing games

Net-BSD == Darkside

Signed Exec AUUG2K

Signed exec only worked with statically linked binaries

Exec path modified

• MD5 hash of disk binary
• compare calculate hash against list loaded into kernel memory
• allow exec if hashed match
• execution speed halved
• cached comparison result for greater speed

developments

• shared libraries
• other hash methods
• now in Net-BSD current kernel source
• name changed to Verified Exec
• nothing signed, just verified

discussion occurred

• verifying executables on untested media, such as NFS and SAN
• “the most vocal people are the ones who think your code is a pile of poo”
• NFS/SAN not in design spec
• In tree code assumes underlying media can be trusted, because of caching

untrusted media

• the kernel assumes that it has total control over everything
• trojan-proof, interesting, much like initial thoughts of verified exec (???)
  • handles untrusted media by checking it every time
  • sendmail from NFS, the check only happens at startup
  • if binary overwritten, and pages forced out of virtual memory, page is loaded from changed binary
  • demonstration code exists to exploit this
• verify pages as they are loaded
  • need to track fingerprint of every single page
• [ prevent changes to executable file, require replacement instead??? No, need to trust file server ]
• Need to modify pager code
  • when pager loads page from storage, the fingerprint is evaluated,
  • if no match, horrible death

Implications

• no need to trust binaries on system
• don’t need to have control over the server
• files can be served from anywhere
• [ can kernel be replaced? ]
• [ can data files be tampered with to cause a security compromise? ]
• [ where is the verification data stored? ]
• kernel level trip wire
• ptrace????
• /dev/mem and /dev/kmem??? turned off with secure level setting
  • =2 cannot open /dev/mem, can’t open raw disk device, etc
  • increased => cannot change fingerprints
• PIC in libraries, no rewriting required
• upgrades to software?
  • go into single user mode
  • firewalls, routers, other stable systems
  • not for development systems
  • not useful for 24/7 systems??? Use multiple systems