Niels Provos Systrace 1.6f and earlier on the x86_64 Linux platform allows local users to bypass intended access restrictions by making a 32-bit syscall with a syscall number that corresponds to a policy-compliant 64-bit syscall, related to race conditions that occur in monitoring 64-bit processes.
http://www.securityfocus.com/archive/1/500377/100/0/threaded
http://www.citi.umich.edu/u/provos/systrace/
http://scarybeastsecurity.blogspot.com/2009/01/bypassing-syscall-filtering.html