Re: [PATCH 2/3] [RFC] seccomp: give BPF x32 bit when restoring x32 filter

On Fri, 2014-07-11 at 12:11 -0400, Paul Moore wrote: > On Thursday, July 10, 2014 09:06:02 PM H. Peter Anvin wrote: > > Incidentally: do seccomp users know that on an x86-64 system you can > > recevie system calls from any of the x86 architectures, regardless of > > how the program is invoked? (This is unusual, so normally denying those > > "alien" calls is the right thing to do.) > > I obviously can't speak for all seccomp users, but libseccomp handles this > by checking the seccomp_data->arch value at the start of the filter and > killing (by default) any non-native architectures. If you want, you can > change this default behavior or add support for other architectures (e.g. > create a filter that allows both x86-64 and x32 but disallows x86, or any > combination of the three for that matter). Maybe libseccomp does some HORRIFIC contortions under the hood, but the interface is crap... Since seccomp_data->arch can't distinguish between X32 and X86_64. If I write a seccomp filter which says KILL arch != x86_64 KILL init_module ALLOW everything else I can still call init_module, I just have to use the X32 variant. If libseccomp is translating: KILL arch != x86_64 into: KILL arch != x86_64 KILL syscall_nr >= 2000 That's just showing how dumb the kernel interface is... Good for you guys, but the kernel is just being dumb :)