linux-kernel - Re: [PATCH v2 security-next 1/4] security: Hornet LSM

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Message-ID: <CAHC9VhTi6+CHD9OtWj5=pPDrtwF+S9yfBOKqghe=9wXmd7jrxA@mail.gmail.com>
Date: Wed, 23 Apr 2025 11:10:29 -0400
From: Paul Moore <paul@...l-moore.com>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, 
	Blaise Boscaccy <bboscaccy@...ux.microsoft.com>, Jonathan Corbet <corbet@....net>, 
	David Howells <dhowells@...hat.com>, Herbert Xu <herbert@...dor.apana.org.au>, 
	"David S. Miller" <davem@...emloft.net>, James Morris <jmorris@...ei.org>, 
	"Serge E. Hallyn" <serge@...lyn.com>, Masahiro Yamada <masahiroy@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, Shuah Khan <shuah@...nel.org>, 
	Mickaël Salaün <mic@...ikod.net>, 
	Günther Noack <gnoack@...gle.com>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Jarkko Sakkinen <jarkko@...nel.org>, 
	Jan Stancek <jstancek@...hat.com>, Neal Gompa <neal@...pa.dev>, 
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	keyrings@...r.kernel.org, 
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, 
	LSM List <linux-security-module@...r.kernel.org>, 
	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	clang-built-linux <llvm@...ts.linux.dev>, nkapron@...gle.com, 
	Matteo Croce <teknoraver@...a.com>, Roberto Sassu <roberto.sassu@...wei.com>, 
	Cong Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH v2 security-next 1/4] security: Hornet LSM

On Wed, Apr 23, 2025 at 10:12 AM James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Mon, 2025-04-21 at 13:12 -0700, Alexei Starovoitov wrote:
> [...]
> > Calling bpf_map_get() and
> > map->ops->map_lookup_elem() from a module is not ok either.
>
> I don't understand this objection.  The program just got passed in to
> bpf_prog_load() as a set of attributes which, for a light skeleton,
> directly contain the code as a blob and have the various BTF
> relocations as a blob in a single element array map.  I think everyone
> agrees that the integrity of the program would be compromised by
> modifications to the relocations, so the security_bpf_prog_load() hook
> can't make an integrity determination without examining both.  If the
> hook can't use the bpf_maps.. APIs directly is there some other API it
> should be using to get the relocations, or are you saying that the
> security_bpf_prog_load() hook isn't fit for purpose and it should be
> called after the bpf core has loaded the relocations so they can be
> provided to the hook as an argument?
>
> The above, by the way, is independent of signing, because it applies to
> any determination that might be made in the security_bpf_prog_load()
> hook regardless of purpose.

I've also been worrying that some of the unspoken motivation behind
the objection is simply that Hornet is not BPF.  If/when we get to a
point where Hornet is sent up to Linus and Alexei's objection to the
Hornet LSM inspecting BPF maps stands, it seems as though *any* LSM,
including BPF LSMs, would need to be prevented from accessing BPF
maps.  I'm fairly certain no one wants to see it come to that.

-- 
paul-moore.com