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Message-ID: <bc260eb8-7a97-48d4-bb6a-6154ae2b2fb5@linux.dev>
Date: Thu, 4 Apr 2024 08:32:27 -0700
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Subject: Re: [PATCH bpf-next 1/2] bpf: Allow invoking kfuncs from
 BPF_PROG_TYPE_SYSCALL progs
Content-Language: en-GB
To: David Vernet <void@manifault.com>, bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
 martin.lau@linux.dev, song@kernel.org, john.fastabend@gmail.com,
 kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org,
 linux-kernel@vger.kernel.org, kernel-team@meta.com
References: <20240404010308.334604-1-void@manifault.com>
From: Yonghong Song <yonghong.song@linux.dev>
In-Reply-To: <20240404010308.334604-1-void@manifault.com>
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On 4/3/24 6:03 PM, David Vernet wrote:
> Currently, a set of core BPF kfuncs (e.g. bpf_task_*, bpf_cgroup_*,
> bpf_cpumask_*, etc) cannot be invoked from BPF_PROG_TYPE_SYSCALL
> programs. The whitelist approach taken for enabling kfuncs makes sense:
> it not safe to call these kfuncs from every program type. For example,
> it may not be safe to call bpf_task_acquire() in an fentry to
> free_task().
>
> BPF_PROG_TYPE_SYSCALL, on the other hand, is a perfectly safe program
> type from which to invoke these kfuncs, as it's a very controlled
> environment, and we should never be able to run into any of the typical
> problems such as recursive invoations, acquiring references on freeing
> kptrs, etc. Being able to invoke these kfuncs would be useful, as
> BPF_PROG_TYPE_SYSCALL can be invoked with BPF_PROG_RUN, and would
> therefore enable user space programs to synchronously call into BPF to
> manipulate these kptrs.
>
> This patch therefore enables invoking the aforementioned core kfuncs
> from BPF_PROG_TYPE_SYSCALL progs.
>
> Signed-off-by: David Vernet <void@manifault.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>