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

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Message-ID: <87plj4jyv9.fsf@microsoft.com>
Date: Wed, 26 Feb 2025 11:21:30 -0800
From: Blaise Boscaccy <bboscaccy@...ux.microsoft.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>, Song Liu
 <song@...nel.org>
Cc: 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

Alexei Starovoitov <alexei.starovoitov@...il.com> writes:

> 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.

Sounds good to me, I'll rework it to use a bool instead.

-blaise