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

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Message-ID: <CAHC9VhS8ST6ODB2pFJTMK4qu8FdM2J=6qEbB=XGxo2ZAZgo1Aw@mail.gmail.com>
Date: Wed, 26 Feb 2025 10:57:24 -0500
From: Paul Moore <paul@...l-moore.com>
To: Song Liu <song@...nel.org>
Cc: Blaise Boscaccy <bboscaccy@...ux.microsoft.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>, linux-security-module@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH 1/1] security: Propagate universal pointer data in bpf hooks

On Wed, Feb 26, 2025 at 2:06 AM 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.

I've only looked at it quickly, but so far it seems reasonable.  I'm
going to take a closer look today.

> Question: Do we need a full bpfptr_t for these hooks, or just a boolean
> "is_kernel or not"?

I may be misunderstanding the patch, but what if we swapped the
existing 'union bpf_attr' parameter for a 'bpfptr_t' parameter?  That
would allow for both kernel and usermode pointers, complete with a
'is_kernel' flag; or am I missing something (likely)?

-- 
paul-moore.com