From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from www62.your-server.de (www62.your-server.de [213.133.104.62]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E0C3B3AD525; Wed, 24 Jun 2026 14:27:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.133.104.62 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782311256; cv=none; b=QM9dnFokXiqxwdI9YqhpocxQGczLbvIfI9c3lTXwAmOZ7QlW6GSeK1xjinw6cCrDv+y37nUKvvcIvOY5o/w3+vWnXB3pvTK/Tvi6Ka0+mQJAGn+dcjWxgMqYKUMkiC3AlUdi0YmbHAMlJm0aibMowDW7QnklOVrVQr/Br5Evqng= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782311256; c=relaxed/simple; bh=pPsUM/wH2/4H3QZBlTY2nn3luV/1PewjVUttuiJuFGU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=khcnN7hAJtVjOL59kjjDwPH7I5gK0jYhFrFBIDjEajhbxkdjOX6kHhnCLPTRe338D/ythLLCKxN/Rq0xkxecn6WitBKbHJMsXLTSFYE2ewAN9i8bhzKyK0ldKU2yEDvP0AWDUxgsd8F+2vUNpdjtfoHjF7giwKcChznTJCBQSbI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=iogearbox.net; spf=pass smtp.mailfrom=iogearbox.net; dkim=pass (2048-bit key) header.d=iogearbox.net header.i=@iogearbox.net header.b=eBvc9bik; arc=none smtp.client-ip=213.133.104.62 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=iogearbox.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=iogearbox.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=iogearbox.net header.i=@iogearbox.net header.b="eBvc9bik" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=iogearbox.net; s=default2302; h=Content-Transfer-Encoding:MIME-Version: Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References; bh=o1AyfKB+ZjGSgVsdsxUpC3h1BPOdh5U+21renvtoT0E=; b=eBvc9bikCuR2GcuxSlrqn7Lg/q T5SDSQYf1omtyZB/eb19QTAqVOPL37VG4G3gjYg6Q0Q+ZUgcYXVvC02bBqwPAjwLRcPQSHQpf1Ohf cD7GUipW4ZHqc2EQ8bz8W2zyWpVk1fbrKC9htIPmNuJoC5AjYdx8OEp3wGgG2w4DOmyfwiR5Prjo2 ObC5AiRPTwmvw4fszDDe+1xGh1s60Wa/H75Dj02URHTfVzbVDuMf+rPUSGLE1t9Z+myUNJhKkXbAv i1nA2NdiUCUjqEJx3b2DGUufdf96zxjlg2IKMQjP5c022xbpa2n3aavWXm8g6xcSk1+2VXXxPDCys g0OzOTMQ==; Received: from localhost ([127.0.0.1]) by www62.your-server.de with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.96.2) (envelope-from ) id 1wcOBy-000GHn-1T; Wed, 24 Jun 2026 16:03:02 +0200 From: Daniel Borkmann To: ast@kernel.org Cc: kpsingh@kernel.org, James.Bottomley@hansenpartnership.com, paul@paul-moore.com, bboscaccy@linux.microsoft.com, memxor@gmail.com, torvalds@linux-foundation.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH bpf-next v2 0/5] Verify BPF signed loader at load time Date: Wed, 24 Jun 2026 16:02:56 +0200 Message-ID: <20260624140301.93421-1-daniel@iogearbox.net> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Virus-Scanned: Clear (ClamAV 1.4.3/28041/Wed Jun 24 08:24:54 2026) The BPF signing scheme signs a light skeleton's loader program and lets the loader vouch for everything else: bpftool bakes the SHA256 of the metadata map into the loader's instructions, signs the instructions, and the loader compares the (frozen, exclusive) map against that hash from within BPF once it runs. The construction is sound as a trusted hash chain, but the kernel itself never attests the metadata, and that split has been the recurring objection from the LSM / integrity side since the scheme was proposed. This proposal closes both gaps by having the kernel verify the metadata at BPF_PROG_LOAD time, before the LSM admission hook and before the verifier, /without/ growing the UAPI. A signed loader binds its metadata map(s) through the existing fd_array/fd_array_cnt, and exclusive maps are already bound to the loader's digest via excl_prog_hash. When a signature is present, the kernel collects the exclusive maps from the fd_array and appends their frozen contents to the instructions before PKCS#7 verification, so the signature covers ... insns || metadata_0 || metadata_1 || [...] ... in fd_array order. The in-loader hash check is dropped from the gen_loader entirely: generated loaders carry no verification logic anymore, and signing or verifying a skeleton becomes an ordinary CMS operation over bytes that sit verbatim in the skeleton, reproducible offline. A signed program is either BPF_SIG_UNSIGNED or BPF_SIG_VERIFIED with nothing in between. There is no new UAPI, we now have a single signature scheme, no LSM code reaching into BPF internals, no new LSM hook, and unsigned loads are completely unaffected. It is also less complex since the loader does not need to deal with BTF, an extra kfunc, etc, as proposed in an earlier series [0]. Tested against full BPF CI which came back green. For more details and examples, see the documentation patch in this series. [0] https://lore.kernel.org/bpf/20260522023234.3778588-1-kpsingh@kernel.org/ v1 -> v2: - Addressed both sashiko complaints, the TOCTOU bug regarding fd_array processing, as well as exclusive map checking to only allow array maps. The validation is now moved into the verifier before the main verification work happens. This also gives the opportunity to utilize the verifier log. Daniel Borkmann (5): bpf: Verify signed loader metadata at load time libbpf: Drop in-loader metadata check for load-time verification bpftool: Cover loader metadata with the program signature selftests/bpf: Verify load-time signed loader metadata Documentation/bpf: Add BPF signing and enforcement doc Documentation/bpf/index.rst | 1 + Documentation/bpf/signing.rst | 490 ++++++++++++++ include/linux/bpf_verifier.h | 1 + kernel/bpf/syscall.c | 81 +-- kernel/bpf/verifier.c | 163 ++++- tools/bpf/bpftool/gen.c | 2 + tools/bpf/bpftool/sign.c | 15 +- tools/lib/bpf/bpf_gen_internal.h | 1 - tools/lib/bpf/gen_loader.c | 76 +-- tools/lib/bpf/skel_internal.h | 27 +- .../selftests/bpf/prog_tests/signed_loader.c | 597 +++++++++++++----- 11 files changed, 1114 insertions(+), 340 deletions(-) create mode 100644 Documentation/bpf/signing.rst -- 2.43.0