linux-kernel - Re: [PATCH bpf-next v4 1/9] bpf: Allow LSM programs to use bpf spin locks

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Message-ID: <20201105203955.ekugupmtjurtdi6h@kafai-mbp.dhcp.thefacebook.com>
Date:   Thu, 5 Nov 2020 12:39:55 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     KP Singh <kpsingh@...omium.org>
CC:     <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>, Paul Turner <pjt@...gle.com>,
        Jann Horn <jannh@...gle.com>, Hao Luo <haoluo@...gle.com>
Subject: Re: [PATCH bpf-next v4 1/9] bpf: Allow LSM programs to use bpf spin
 locks

On Thu, Nov 05, 2020 at 03:47:47PM +0100, KP Singh wrote:
> From: KP Singh <kpsingh@...gle.com>
> 
> Usage of spin locks was not allowed for tracing programs due to
> insufficient preemption checks. The verifier does not currently prevent
> LSM programs from using spin locks, but the helpers are not exposed
> via bpf_lsm_func_proto.
> 
> Based on the discussion in [1], non-sleepable LSM programs should be
> able to use bpf_spin_{lock, unlock}.
> 
> Sleepable LSM programs can be preempted which means that allowng spin
> locks will need more work (disabling preemption and the verifier
> ensuring that no sleepable helpers are called when a spin lock is held).
> 
> [1]: https://lore.kernel.org/bpf/20201103153132.2717326-1-kpsingh@chromium.org/T/#md601a053229287659071600d3483523f752cd2fb
> 
> Signed-off-by: KP Singh <kpsingh@...gle.com>
Acked-by: Martin KaFai Lau <kafai@...com>