Messages in this thread | | | Date | Mon, 14 Sep 2015 18:48:43 +0200 | From | Daniel Borkmann <> | Subject | Re: [PATCH v2 2/5] seccomp: make underlying bpf ref counted as well |
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On 09/14/2015 06:00 PM, Tycho Andersen wrote: > On Fri, Sep 11, 2015 at 08:28:19PM +0200, Daniel Borkmann wrote: >> I think due to the given insns restrictions on classic seccomp, this >> could work for "most cases" (see below) for the time being until pointer >> sanitation is resolved and that seccomp-only restriction from the dump >> could be removed, > > Ok, thanks. > >> BUT there's one more stone in the road which you still >> need to take care of with this whole 'giving classic seccomp-BPF -> eBPF >> transforms an fd, dumping and restoring that via bpf(2)' approach: >> >> If you have JIT enabled on ARM32, and add a classic seccomp-BPF filter, >> and dump that via your bpf(2) interface based on the current patches, what >> you'll get is not eBPF opcodes but classic (!) BPF opcodes as ARM32 classic >> JIT supports compilation of seccomp, since commit 24e737c1ebac ("ARM: net: >> add JIT support for loads from struct seccomp_data."). >> >> So in that case, bpf_prepare_filter() will not call into bpf_migrate_filter() >> as there's simply no need for it, because the classic code could already >> be JITed there. I guess other archs where JIT support for eBPF in not yet >> within near sight might sooner or later support this insn for their classic >> JITs, too ... > > Thanks for pointing this out. > > What if we legislate that the output of bpf(BPF_PROG_DUMP, ...) is > always eBPF? As near as I can tell there is no way to determine if a > struct bpf_prog is classic or eBPF, so we'd need to add a bit to > indicate whether or not the prog has been converted so that > BPF_PROG_DUMP knows when to convert it.
As I said, you have bpf_prog_was_classic() function to determine exactly this (so without your type re-assignment you have a way to distinguish it).
Wouldn't it be much easier to rip this set apart into multiple ones, solving one individual thing at a time, f.e. starting out simple and 1) only add native eBPF support to seccomp, after that 2) add a method to dump native-only eBPF programs for criu, then 3) think about a right interface for classic BPF seccomp dumping, etc, etc? Currently, it tries to solve everything at once, and with some early assumptions that have non-trivial side-effects.
Thanks, Daniel
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