linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Make the pointer returned by iter next method valid

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Message-ID: <CAADnVQ+=nGLgj=HOiquvzKJv3WZ320HPduNms8OujZtv65fV4Q@mail.gmail.com>
Date: Tue, 20 Aug 2024 08:28:54 +0200
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Juntong Deng <juntong.deng@...look.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>, 
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: Make the pointer returned by iter next
 method valid

On Mon, Aug 19, 2024 at 6:24 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> > >
> > > [0]:
> > > https://lore.kernel.org/bpf/CAP01T75na=fz7EhrP4Aw0WZ33R7jTbZ4BcmY56S1xTWczxHXWw@mail.gmail.com/
> > >
> > > Maybe we can have more discussion?
> > >
> > > (This email has been CC Kumar)
> >
> > +1
> > pointer from iterator should always be trusted except
> > the case of KF_RCU_PROTECTED iterators.
> > Those iters clear iter itself outside of RCU CS,
> > so a pointer returned from iter_next should probably be
> > PTR_TO_BTF_ID | MEM_RCU | PTR_MAYBE_NULL.
> >
> > For all other iters it should be safe to return
> > PTR_TO_BTF_ID | PTR_TRUSTED | PTR_MAYBE_NULL
> >
>
> Ok, but we at some point might need to return a non-RCU/non-trusted
> pointer, so I guess we'll have to add yet another flag to opt-out of
> "trustedness"?

If such case ever happens then yes, we'd need a new flag,
but I don't see it's happening