linux-kernel - Re: [PATCH 1/1] security: Propagate universal pointer data in bpf hooks

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Message-ID: <CAADnVQJWMBRspP-srQwe8_B1smGG1hs3kVbpeiuYo-0mLWAnUA@mail.gmail.com>
Date: Wed, 26 Feb 2025 08:00:21 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Song Liu <song@...nel.org>
Cc: Blaise Boscaccy <bboscaccy@...ux.microsoft.com>, Paul Moore <paul@...l-moore.com>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.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>, Eduard Zingerman <eddyz87@...il.com>, 
	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>, 
	Stephen Smalley <stephen.smalley.work@...il.com>, Ondrej Mosnacek <omosnace@...hat.com>, 
	LSM List <linux-security-module@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	bpf <bpf@...r.kernel.org>, selinux@...r.kernel.org
Subject: Re: [PATCH 1/1] security: Propagate universal pointer data in bpf hooks

On Tue, Feb 25, 2025 at 11:06 PM Song Liu <song@...nel.org> wrote:
>
> On Tue, Feb 25, 2025 at 4:31 PM Blaise Boscaccy
> <bboscaccy@...ux.microsoft.com> wrote:
> >
> > Certain bpf syscall subcommands are available for usage from both
> > userspace and the kernel. LSM modules or eBPF gatekeeper programs may
> > need to take a different course of action depending on whether or not
> > a BPF syscall originated from the kernel or userspace.
> >
> > Additionally, some of the bpf_attr struct fields contain pointers to
> > arbitrary memory. Currently the functionality to determine whether or
> > not a pointer refers to kernel memory or userspace memory is exposed
> > to the bpf verifier, but that information is missing from various LSM
> > hooks.
> >
> > Here we augment the LSM hooks to provide this data, by simply passing
> > the corresponding universal pointer in any hook that contains already
> > contains a bpf_attr struct that corresponds to a subcommand that may
> > be called from the kernel.
>
> I think this information is useful for LSM hooks.
>
> Question: Do we need a full bpfptr_t for these hooks, or just a boolean
> "is_kernel or not"?

+1
Just passing the bool should do.
Passing uattr is a footgun. Last thing we need is to open up TOCTOU concerns.