netdev - Re: [PATCH bpf-next V1] bpf: devmap dynamic map-value area based on BTF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQKWj_eoVE9XLqwEX2ZWB_yLwRtuQqY7EuFZSNZd40ukPQ@mail.gmail.com>
Date:   Fri, 5 Jun 2020 09:58:26 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     David Ahern <dsahern@...il.com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH bpf-next V1] bpf: devmap dynamic map-value area based on BTF

On Fri, Jun 5, 2020 at 1:23 AM Jesper Dangaard Brouer <brouer@...hat.com> wrote:
>
> Great. If we can remove this requirement of -1 init (and let zero mean
> feature isn't used), then I'm all for exposing expose in uapi/bpf.h.

Not having it in bpf.h doesn't magically make it invisible.
It's uapi because user space C sources rely on its fixed format.
vmlinux.h contains all kernel types. both uapi and kernel internal.
devmap selftest taking uapi 'struct bpf_devmap_val' from vmlinux.h is
an awful hack.
I prefer to keep vmlinux.h usage to bpf programs only.
User space C code should interface with kernel via proper uapi headers.
When vmlinux.h is used by bpf C program it's completely different from
user space C code doing the same, because llvm emits relocations for
bpf prog and libbpf adjusts them.
So doing 'foo->bar' in bpf C is specific to target kernel, whereas
user C code 'foo->bar' is a hard constant which bakes it into uapi
that kernel has to keep backwards compatible.
If in some distant future we teach both gcc and clang to do bpf-style
relocations for x86 and teach ld.so to adjust them then we can dream
about very differently looking kernel/user interfaces.
Right now any struct used by user C code and passed into kernel is uapi.