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Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs

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On 10/5/15 2:00 PM, Kees Cook wrote:
> On Mon, Oct 5, 2015 at 1:48 PM, Alexei Starovoitov<ast@plumgrid.com>  wrote:
>> >In order to let unprivileged users load and execute eBPF programs
>> >teach verifier to prevent pointer leaks.
>> >Verifier will prevent
>> >- any arithmetic on pointers
>> >   (except R10+Imm which is used to compute stack addresses)
>> >- comparison of pointers
>> >- passing pointers to helper functions
>> >- indirectly passing pointers in stack to helper functions
>> >- returning pointer from bpf program
>> >- storing pointers into ctx or maps
> Does the arithmetic restriction include using a pointer as an index to
> a maps-based tail call? I'm still worried about pointer-based
> side-effects.

the array maps that hold FDs (BPF_MAP_TYPE_PROG_ARRAY and
BPF_MAP_TYPE_PERF_EVENT_ARRAY) don't have lookup/update accessors
from the program side, so programs cannot see or manipulate
those pointers.
For the former only bpf_tail_call() is allowed that takes integer
index and jumps to it. And the latter map accessed with
bpf_perf_event_read() that also takes index only (this helper
is not available to socket filters anyway).
Also bpf_tail_call() can only jump to the program of the same type.
So I'm quite certain it's safe.

Yes, please ask questions and try to poke holes. Now it is time.

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Thread

[PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-05 22:50 +0200
  Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Kees Cook <keescook@chromium.org> - 2015-10-05 23:10 +0200
    Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Andy Lutomirski <luto@amacapital.net> - 2015-10-05 23:20 +0200
      Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-05 23:40 +0200
    Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-05 23:20 +0200
      Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Kees Cook <keescook@chromium.org> - 2015-10-06 00:10 +0200
        Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-06 02:30 +0200
  Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Daniel Borkmann <daniel@iogearbox.net> - 2015-10-06 00:20 +0200
    Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-06 03:00 +0200
      Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Ingo Molnar <mingo@kernel.org> - 2015-10-06 09:20 +0200
        Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Daniel Borkmann <daniel@iogearbox.net> - 2015-10-06 10:10 +0200
          Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Ingo Molnar <mingo@kernel.org> - 2015-10-06 10:30 +0200
            Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Daniel Borkmann <daniel@iogearbox.net> - 2015-10-06 10:50 +0200
              Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-06 20:00 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Eric Dumazet <eric.dumazet@gmail.com> - 2015-10-06 20:00 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Andy Lutomirski <luto@amacapital.net> - 2015-10-06 20:10 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Ingo Molnar <mingo@kernel.org> - 2015-10-07 08:10 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-06 21:30 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Daniel Borkmann <daniel@iogearbox.net> - 2015-10-06 20:10 +0200
      Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Daniel Borkmann <daniel@iogearbox.net> - 2015-10-06 14:50 +0200
        Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-07 23:30 +0200
          Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Daniel Borkmann <daniel@iogearbox.net> - 2015-10-08 00:10 +0200
            Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Kees Cook <keescook@chromium.org> - 2015-10-08 00:30 +0200
              Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-08 01:50 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Ingo Molnar <mingo@kernel.org> - 2015-10-08 08:30 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-08 08:40 +0200
                Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Kees Cook <keescook@chromium.org> - 2015-10-08 19:50 +0200
  Re: [PATCH net-next 1/2] bpf: enable non-root eBPF programs Alexei Starovoitov <ast@plumgrid.com> - 2015-10-08 04:30 +0200

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