linux-kernel - Re: [PATCH bpf-next v4 3/6] mm: introduce bpf_get_root_mem

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: <CAADnVQJr0WqmqA2fQeC0=Jn5F-ujWmUkL-GfT6Jbv8jiQwCAMw@mail.gmail.com>
Date: Mon, 5 Jan 2026 08:05:54 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Matt Bobrowski <mattbobrowski@...gle.com>, Kumar Kartikeya Dwivedi <memxor@...il.com>, 
	Tejun Heo <tj@...nel.org>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>, bpf <bpf@...r.kernel.org>, 
	linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, 
	JP Kobryn <inwardvessel@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Michal Hocko <mhocko@...nel.org>, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH bpf-next v4 3/6] mm: introduce bpf_get_root_mem_cgroup()
 BPF kfunc

On Sun, Jan 4, 2026 at 11:49 PM Matt Bobrowski <mattbobrowski@...gle.com> wrote:
>
> >
> > No need for a new KF flag. Any struct returned by kfunc should be
> > trusted or trusted_or_null if KF_RET_NULL was specified.
> > I don't remember off the top of my head, but this behavior
> > is already implemented or we discussed making it this way.
>
> Hm, I do not see any evidence of this kind of semantic currently
> implemented, so perhaps it was only discussed at some point. Would you
> like me to put forward a patch that introduces this kind of implicit
> trust semantic for BPF kfuncs returning pointer to struct types?

Hmm. What about these:
BTF_ID_FLAGS(func, scx_bpf_cpu_rq)
BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL)
BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_RET_NULL | KF_RCU_PROTECTED)

I thought they're returning a trusted pointer without acquiring it.
iirc the last one returns trusted in RCU CS,
but the first two return just a legacy ptr_to_btf_id ?
This is something to fix asap then.