netdev - Re: [PATCH v4 bpf-next 1/9] bpf: introduce bpf_spin

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]

Message-ID: <20190130022012.suxxs4h4z5qfbrdf@ast-mbp.dhcp.thefacebook.com>
Date:   Tue, 29 Jan 2019 18:20:14 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net,
        daniel@...earbox.net, jakub.kicinski@...ronome.com,
        netdev@...r.kernel.org, kernel-team@...com, mingo@...hat.com,
        will.deacon@....com, Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        jannh@...gle.com
Subject: Re: [PATCH v4 bpf-next 1/9] bpf: introduce bpf_spin_lock

On Tue, Jan 29, 2019 at 09:59:03AM +0100, Peter Zijlstra wrote:
> On Mon, Jan 28, 2019 at 01:37:12PM -0800, Alexei Starovoitov wrote:
> > On Mon, Jan 28, 2019 at 09:43:10AM +0100, Peter Zijlstra wrote:
> 
> > > Isn't that still broken? AFAIU networking progs can happen in task
> > > context (TX) and SoftIRQ context (RX), which can nest.
> > 
> > Sure. sendmsg side of networking can be interrupted by napi receive.
> > Both can have bpf progs attached at different points, but napi won't run
> > when bpf prog is running, because bpf prog disables preemption.
> 
> Disabling preemption is not sufficient, it needs to have done
> local_bh_disable(), which isn't unlikely given this is all networking
> code.

right. excellent point. Since bh is not disabled nesting of the sender side
socket filter is possible with receive side socket filter.
Theoretically the same socket filter prog can be nested.
I believe it's fine with the current state of things including
parrallel access to bpf maps
(my patch to add preempt_disable around socket filter is still needed).
But this point regarding local_bh_disable changes the plans for bpf_spin_lock.
We'd need local_bh_disable around socket filters and around syscall access
to map with 'struct bpf_spin_lock' or two new helpers bpf_spin_lock_irqsave
and corresponding verifier support.
I guess we'll argue about best option when that time comes.
For now there will be no bpf_spin_lock in socket filters and I need to
add local_bh_disable for syscall access to maps with bpf_spin_lock
to avoid deadlock.
I'll send a set of fixes for lockdep false positives and
respin bpf_spin_lock set.