netdev - Re: [PATCH bpf-next v2 1/7] bpf: implement lookup-free direct value access

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:   Fri, 1 Mar 2019 12:08:13 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>, bpf@...r.kernel.org,
        Networking <netdev@...r.kernel.org>,
        Joe Stringer <joe@...d.net.nz>,
        john fastabend <john.fastabend@...il.com>, tgraf@...g.ch,
        Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>,
        lmb@...udflare.com
Subject: Re: [PATCH bpf-next v2 1/7] bpf: implement lookup-free direct value
 access

On Fri, 1 Mar 2019 11:35:17 -0800, Andrii Nakryiko wrote:
> > > Do you think that would work? Using array is a bit limiting, because
> > > it doesn't allow to do partial reads/updates, while BPF_MAP_TYPE_HEAP
> > > would be single big value that allows partial reading/updating.  
> >
> > If I understand it correctly, the main difference this would have is
> > to be able to use spin_locks in a more fine-grained fashion, right?  
> 
> spin_lock is just a nice bonus, if there is any manipulation that
> isn't <= 8 byte long that needs to be done atomically.
> 
> The reason for this new type of map is actually ability to update
> global variables from outside BPF program in granular fashion. E.g.,
> turning on some extra debug output temporarily, tuning parameters,
> changing PID to trace, etc, without stopping and reloading BPF
> program. With array, it's all-or-nothing: to update anything you have
> to overwrite entire .data section. As I mentioned, if we can get BTF
> type information for entirety of .data, it would allow to manipulate
> those variables by name even with generic tools like bpftool.

Sounds like you'd almost want to mmap the value ;)