CVE request: kernel: x86-64: syscall-audit: 32/64 syscall hole

[Eugene Teo <eugeneteo () kernel sg>]

On x86-64, a 32-bit process (TIF_IA32) can switch to 64-bit mode with
ljmp, and then use the "syscall" instruction to make a 64-bit system
call.  A 64-bit process make a 32-bit system call with int $0x80.

In both these cases, audit_syscall_entry() will use the wrong system
call number table and the wrong system call argument registers.  This
could be used to circumvent a syscall audit configuration that filters
based on the syscall numbers or argument details.

Credit: Roland McGrath.

References:
https://bugzilla.redhat.com/show_bug.cgi?id=487990
http://scary.beasts.org/security/CESA-2009-001.html
http://lkml.org/lkml/2009/2/27/451 summary
http://lkml.org/lkml/2009/2/27/452 syscall-audit
http://lkml.org/lkml/2009/2/27/453 seccomp