netdev - Re: [PATCH bpf-next 2/8] tools: bpftool: add probes for /proc/ eBPF parameters

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Date:   Sat, 15 Dec 2018 00:40:56 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Quentin Monnet <quentin.monnet@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Stanislav Fomichev <sdf@...gle.com>
Subject: Re: [PATCH bpf-next 2/8] tools: bpftool: add probes for /proc/ eBPF
 parameters

On 12/13/2018 01:19 PM, Quentin Monnet wrote:
> Add a set of probes to dump the eBPF-related parameters available from
> /proc/: availability of bpf() syscall for unprivileged users,
> JIT compiler status and hardening status, kallsyms exports status.
> 
> Sample output:
> 
>     # bpftool feature probe kernel
>     Scanning system configuration...
>     bpf() syscall for unprivileged users is enabled
>     JIT compiler is disabled
>     JIT compiler hardening is disabled
>     JIT compiler kallsyms exports are disabled
>     ...
> 
>     # bpftool --json --pretty feature probe kernel
>     {
>         "system_config": {
>             "unprivileged_bpf_disabled": 0,
>             "bpf_jit_enable": 0,
>             "bpf_jit_harden": 0,
>             "bpf_jit_kallsyms": 0
>         },
>         ...
>     }
> 
>     # bpftool feature probe kernel macros prefix BPFTOOL_
>     #define UNPRIVILEGED_BPF_DISABLED UNPRIVILEGED_BPF_DISABLED_OFF
>     #define  UNPRIVILEGED_BPF_DISABLED_OFF 0
>     #define  UNPRIVILEGED_BPF_DISABLED_ON 1
>     #define  UNPRIVILEGED_BPF_DISABLED_UNKNOWN -1
>     #define JIT_COMPILER_ENABLE JIT_COMPILER_ENABLE_OFF
>     #define  JIT_COMPILER_ENABLE_OFF 0
>     #define  JIT_COMPILER_ENABLE_ON 1
>     #define  JIT_COMPILER_ENABLE_ON_WITH_DEBUG 2
>     #define  JIT_COMPILER_ENABLE_UNKNOWN -1
>     #define JIT_COMPILER_HARDEN JIT_COMPILER_HARDEN_OFF
>     #define  JIT_COMPILER_HARDEN_OFF 0
>     #define  JIT_COMPILER_HARDEN_FOR_UNPRIVILEGED 1
>     #define  JIT_COMPILER_HARDEN_FOR_ALL_USERS 2
>     #define  JIT_COMPILER_HARDEN_UNKNOWN -1
>     #define JIT_COMPILER_KALLSYMS JIT_COMPILER_KALLSYMS_OFF
>     #define  JIT_COMPILER_KALLSYMS_OFF 0
>     #define  JIT_COMPILER_KALLSYMS_FOR_ROOT 1
>     #define  JIT_COMPILER_KALLSYMS_UNKNOWN -1
>     ...

Hm, given these knobs may change at any point in time, what would
be a use case in an application for these if they cannot be relied
upon? (At least the jit_enable and jit_harden are transparent to
the user.)