From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2216217A305; Fri, 30 May 2025 22:14:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748643300; cv=none; b=r3pzwVOYPW7KfW6Y62z5Xt2TQjMJ7Iy6KpSeKIrxvPHEFF3t81bApeq3ml7hvHXtpyzXOvjtphUZy25RWLJikzznu4ReCgspfqiKvC92GQMVMRGdLwiqj1UerofusmPnM5uBg4IQPj1AZNAScRfRNAuo+OUTD92uN/Y7FUic7F8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748643300; c=relaxed/simple; bh=Ha9HitzJEtwAtpqw1vyq310D5z7WewaMzLivpC+CLU0=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=oWUPTb9VoVU24yCsUWPqDLJueTXuVvHon5vaUkcqZ6xWUDNQrL71B5uJmv9hp9WtcJm9Ny+kysPsxsQzeCXON8Iz3q0lysavGjLpNxBhh9d9BdozcKCQujHHDlX1uWcy8ikvsFORrTUXK6WiUvQG5AbuYk9M9sJnc0Vyf0esA5c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=jBwDxGtx; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="jBwDxGtx" Received: from narnia (unknown [40.118.131.60]) by linux.microsoft.com (Postfix) with ESMTPSA id A4C1B2078637; Fri, 30 May 2025 15:14:49 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com A4C1B2078637 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1748643292; bh=tl7GCrQlw6JiLCRWe2kPhYZkShEGu834PJi0NfyWgOQ=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=jBwDxGtx/DxaHdgQXJx/fxeM35VCFgJd5Aylex7yBELfkVjaH7a93yyzy0x2C1BeN k1mcSHSDKLO/RGzwGu5f/F2H31dmRI0+Os5CqqcAUWn6X6nznQ+htMvYy1jThBAnNG xakNB9qxdpDHuZ3i3IqDD7Ezb86VQwsBqj0CG/bY= From: Blaise Boscaccy To: KP Singh Cc: Paul Moore , jarkko@kernel.org, zeffron@riotgames.com, xiyou.wangcong@gmail.com, kysrinivasan@gmail.com, code@tyhicks.com, linux-security-module@vger.kernel.org, roberto.sassu@huawei.com, James.Bottomley@hansenpartnership.com, Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , Stanislav Fomichev , Hao Luo , Jiri Olsa , David Howells , Lukas Wunner , Ignat Korchagin , Quentin Monnet , Jason Xing , Willem de Bruijn , Anton Protopopov , Jordan Rome , Martin Kelly , Alan Maguire , Matteo Croce , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org, linux-crypto@vger.kernel.org, kys@microsoft.com Subject: Re: [PATCH 0/3] BPF signature verification In-Reply-To: References: <20250528215037.2081066-1-bboscaccy@linux.microsoft.com> <87iklhn6ed.fsf@microsoft.com> Date: Fri, 30 May 2025 15:14:48 -0700 Message-ID: <87ecw5n3tz.fsf@microsoft.com> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable KP Singh writes: > On Fri, May 30, 2025 at 11:19=E2=80=AFPM Blaise Boscaccy > wrote: >> >> KP Singh writes: >> > > [...] > >> > >> >> And that isn't at odds with the kernel being able to do it nor is it >> with what I posted. >> >> > If your build environment that signs the BPF program is compromised >> > and can inject arbitrary code, then signing does not help. Can you >> > explain what a supply chain attack would look like here? >> > >> >> Most people here can read C code. The number of people that can read >> ebpf assembly metaprogramming code is much smaller. Compromising clang >> is one thing, compromising libbpf is another. Your proposal increases >> the attack surface with no observable benefit. If I was going to leave a >> hard-to-find backdoor into ring0, gen.c would be a fun place to explore >> doing it. Module and UEFI signature verification code doesn't live >> inside of GCC or Clang as set of meta-instructions that get emitted, and >> there are very good reasons for that. >> >> Further, since the signature verification code is unique for each and >> every program it needs to be verified/proved/tested for each and every >> program. Additionally, since all these checks are being forced outside >> of the kernel proper, with the insistence of keeping the LSM layer in >> the dark of the ultimate result, the only way to test that a program >> will fail if the map is corrupted is to physically corrupt each and >> every program and test that individually. That isn't "elegant" nor "user >> friendly" in any way, shape or form. >> >> >> subsystem. Additionally, it is impossible to verify the code >> >> performing the signature verification, as it is uniquely regenerated >> > >> > The LSM needs to ensure that it allows trusted LOADER programs i.e. >> > with signatures and potentially trusted signed user-space binaries >> > with unsigned or delegated signing (this will be needed for Cilium and >> > bpftrace that dynamically generate BPF programs), that's a more >> > important aspect of the LSM policy from a BPF perspective. >> > >> >> I would like to be able to sign my programs please and have the kernel >> verify it was done correctly. Why are you insisting that I *don't* do >> that? I'm yet to see any technical objection to doing that. Do you have >> one that you'd like to share at this point? > > The kernel allows a trusted loader that's signed with your private > key, that runs in the kernel context to delegate the verification. > This pattern of a trusted / delegated loader is going to be required > for many of the BPF use-cases that are out there (Cilium, bpftrace) > that dynamically generate eBPF programs. > > The technical objection is that: > > * It does not align with most BPF use-cases out there as most > use-cases need a trusted loader. No, it's definitely a use case. It's trivial to support both a trusted loader and a signature over the hash chain of supplied assets. > * Locks us into a UAPI, whereas a signed LOADER allows us to > incrementally build signing for all use-cases without compromising the > security properties. > Your proposal locks us into a UAPI as well. There is no way to make to do this via UAPI without making a UAPI design choice. > BPF's philosophy is that of flexibility and not locking the users into > a rigid in-kernel implementation and UAPI. > Then why are you locking us into a rigid only-signing-the-loader-is-allowed implementation? > - KP > >> >> > MAP_EXCLUSIVE is missing and is required which prevents maps from >> > being accessed by other programs as explained in the proposal. >> > >> > Please hold off on further iterations, I am working on a series and >> > will share these patches based on the design that was proposed. >> > >> >> So the premise here seems to be that people should only be allowed to >> sign trusted loaders, and that trusted loaders must additionally be >> authored by you, correct? >> >> When can we expect to see your patchset posted? >> >> >> >> >> for every program. >> >> >> >> >> >> >> >> 2. Timing of Signature Check >> >> >> >> This patchset moves the signature check to a point before >> >> security_bpf_prog_load is invoked, due to an unresolved discussion >> >> here: >> > >> > This is fine and what I had in mind, signature verification does not >> > need to happen in the verifier and the existing hooks are good enough. >> > I did not reply to Paul's comment since this is a fairly trivial >> > detail and would be obvious in the implementation that the verifier is >> > not the right place to check the signature anyways as the instruction >> > buffer is only stable pre-verification. >> > >> >> https://lore.kernel.org/linux-security-module/CAHC9VhTj3=3DZXgrYMNA+G= 64zsOyZO+78uDs1g=3Dkh91=3DGR5KypYg@mail.gmail.com/ >> >> This change allows the LSM subsystem to be informed of the signature >> >> verification result=E2=80=94if it occurred=E2=80=94and the method use= d, all without >> >> introducing a new hook. It improves visibility and auditability, >> >> reducing the =E2=80=9Ctrust me, friend=E2=80=9D aspect of the origina= l design. >> > >> > >> > On Wed, May 28, 2025 at 11:50=E2=80=AFPM Blaise Boscaccy >> > wrote: >> >> >> >> As suggested or mandated by KP Singh >> >> https://lore.kernel.org/linux-security-module/CACYkzJ6VQUExfyt0=3D-Fm= Xz46GHJh3d=3DFXh5j4KfexcEFbHV-vg@mail.gmail.com/, >> >> this patchset proposes and implements an alternative hash-chain >> >> algorithm for signature verification of BPF programs. >> >> >> >> This design diverges in two key ways: >> >> >> >> 1. Signature Strategy >> >> >> >> Two different signature strategies are >> >> implemented. One verifies only the signature of the loader program in >> >> the kernel, as described in the link above. The other verifies the >> >> program=E2=80=99s maps in-kernel via a hash chain. The original desi= gn >> >> required loader programs to be =E2=80=9Cself-aborting=E2=80=9D and em= bedded the >> >> terminal hash verification logic as metaprogramming code generation >> >> routines inside libbpf. While this patchset supports that scheme, it >> >> is considered undesirable in certain environments due to the potential >> >> for supply-chain attack vectors and the lack of visibility for the LSM >> >> subsystem. Additionally, it is impossible to verify the code >> >> performing the signature verification, as it is uniquely regenerated >> >> for every program. >> >> >> >> 2. Timing of Signature Check >> >> >> >> This patchset moves the signature check to a point before >> >> security_bpf_prog_load is invoked, due to an unresolved discussion >> >> here: >> >> https://lore.kernel.org/linux-security-module/CAHC9VhTj3=3DZXgrYMNA+G= 64zsOyZO+78uDs1g=3Dkh91=3DGR5KypYg@mail.gmail.com/ >> >> This change allows the LSM subsystem to be informed of the signature >> >> verification result=E2=80=94if it occurred=E2=80=94and the method use= d, all without >> >> introducing a new hook. It improves visibility and auditability, >> >> reducing the =E2=80=9Ctrust me, friend=E2=80=9D aspect of the origina= l design. >> >> >> >> >> >> Blaise Boscaccy (3): >> >> bpf: Add bpf_check_signature >> >> bpf: Support light-skeleton signatures in autogenerated code >> >> bpftool: Allow signing of light-skeleton programs >> >> >> >> include/linux/bpf.h | 2 + >> >> include/linux/verification.h | 1 + >> >> include/uapi/linux/bpf.h | 4 + >> >> kernel/bpf/arraymap.c | 11 +- >> >> kernel/bpf/syscall.c | 123 +++++++++++++++++++- >> >> tools/bpf/bpftool/Makefile | 4 +- >> >> tools/bpf/bpftool/common.c | 204 +++++++++++++++++++++++++++++++= ++ >> >> tools/bpf/bpftool/gen.c | 66 ++++++++++- >> >> tools/bpf/bpftool/main.c | 24 +++- >> >> tools/bpf/bpftool/main.h | 23 ++++ >> >> tools/include/uapi/linux/bpf.h | 4 + >> >> tools/lib/bpf/libbpf.h | 4 + >> >> tools/lib/bpf/skel_internal.h | 28 ++++- >> >> 13 files changed, 491 insertions(+), 7 deletions(-) >> >> >> >> -- >> >> 2.48.1 >> >>