From patchwork Tue Aug 20 00:18:01 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Garrett X-Patchwork-Id: 11102395 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B97C31398 for ; Tue, 20 Aug 2019 00:19:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D69C22D37 for ; Tue, 20 Aug 2019 00:19:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Pbcszmfo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729189AbfHTATS (ORCPT ); Mon, 19 Aug 2019 20:19:18 -0400 Received: from mail-vs1-f74.google.com ([209.85.217.74]:46339 "EHLO mail-vs1-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729176AbfHTATQ (ORCPT ); Mon, 19 Aug 2019 20:19:16 -0400 Received: by mail-vs1-f74.google.com with SMTP id b129so1390606vsd.13 for ; Mon, 19 Aug 2019 17:19:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=l0D0FijjHNavvE4x6KoSMcY6aVnPYpY2dpif/cNLitk=; b=Pbcszmfo0nBO9MridqaWaCmAvMTSKzWZF5bf08oJsft5Gw9UdsClZ/3l8pVt1WW3Om TeGXyUuWLHjajfOp9UAv1xzvhVCFEKDt2R6Hf7PPozGHpMUpP//3XuQkUqhZQu6yWFoc SD3i9b1jcaZZckls08n4PzLiiUYetxGJ9giY/QjFgDTVYN+AYAI5z4FRN0xNphj1z5BS 8Y4fM5nAzyU3sAOr9QG9Z0qxuksHBXeIpeg2XkOp2JBO/xlZMbp1xjBpaBVrTrm1BbW3 NincUSfhrlYLkkDB2M9Olx0VH03LJD82RbEe014R/lSjMxZcJylmUsPtdpN3ZNOHNslE wrVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=l0D0FijjHNavvE4x6KoSMcY6aVnPYpY2dpif/cNLitk=; b=o8dVkqOXBkhisvObDUVijFI7Yg9rcq+kB6XWUXXz1rzKzO1dLivWQWf/3oEAfvLFpf 2ZuW9BXlSP3daLwMX+XnPAW2aymHXREznVvFozvzhb3uhQQDOBrJfHL4ntA3Zw3Pf7Av 2yh6Ld1N6ZHudPhtwkB1ul67wRu1fScCDWOdIXlX2Wbq37AGyoDR9UBJE1vuH/MelPov D3L1osby8cZUMApcj9RCaieTU80LuQVNo7FZpQRnFNTFQWScWG/2Ah/T18Cv/Rqm3x8l PUpbbeOyK9GSoxiMPLY11Xs43EPYq4IFHz0pExvoizejtkLNhHjQwh1FrHy8oxPXRlk9 l1nA== X-Gm-Message-State: APjAAAWx2PkRL6tZfHlRvUsPuDYd38NbZkpN7sHl9bHHMgR3nnPkZF7/ GvfLIQKXavSmptfRkBorhfj2HBxtHsIb2Lt9xQMnJA== X-Google-Smtp-Source: APXvYqx2L3MW/1bgQUg45dA1Z91iTEEgqOs4v9WdbRnDoWq8eMf71SjwOalt9zG3ldR2tj+5WPs9XJ17SMP/l8HXZoR6rw== X-Received: by 2002:a1f:7c0e:: with SMTP id x14mr9606134vkc.0.1566260355122; Mon, 19 Aug 2019 17:19:15 -0700 (PDT) Date: Mon, 19 Aug 2019 17:18:01 -0700 In-Reply-To: <20190820001805.241928-1-matthewgarrett@google.com> Message-Id: <20190820001805.241928-26-matthewgarrett@google.com> Mime-Version: 1.0 References: <20190820001805.241928-1-matthewgarrett@google.com> X-Mailer: git-send-email 2.23.0.rc1.153.gdeed80330f-goog Subject: [PATCH V40 25/29] kexec: Allow kexec_file() with appropriate IMA policy when locked down From: Matthew Garrett To: jmorris@namei.org Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Matthew Garrett , Matthew Garrett , Mimi Zohar , Dmitry Kasatkin , linux-integrity@vger.kernel.org Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: Systems in lockdown mode should block the kexec of untrusted kernels. For x86 and ARM we can ensure that a kernel is trustworthy by validating a PE signature, but this isn't possible on other architectures. On those platforms we can use IMA digital signatures instead. Add a function to determine whether IMA has or will verify signatures for a given event type, and if so permit kexec_file() even if the kernel is otherwise locked down. This is restricted to cases where CONFIG_INTEGRITY_TRUSTED_KEYRING is set in order to prevent an attacker from loading additional keys at runtime. Signed-off-by: Matthew Garrett Acked-by: Mimi Zohar Cc: Dmitry Kasatkin Cc: linux-integrity@vger.kernel.org Signed-off-by: James Morris --- include/linux/ima.h | 9 ++++++ kernel/kexec_file.c | 10 +++++- security/integrity/ima/ima.h | 2 ++ security/integrity/ima/ima_main.c | 2 +- security/integrity/ima/ima_policy.c | 50 +++++++++++++++++++++++++++++ 5 files changed, 71 insertions(+), 2 deletions(-) diff --git a/include/linux/ima.h b/include/linux/ima.h index 00036d2f57c3..8e2f324fb901 100644 --- a/include/linux/ima.h +++ b/include/linux/ima.h @@ -129,4 +129,13 @@ static inline int ima_inode_removexattr(struct dentry *dentry, return 0; } #endif /* CONFIG_IMA_APPRAISE */ + +#if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING) +extern bool ima_appraise_signature(enum kernel_read_file_id func); +#else +static inline bool ima_appraise_signature(enum kernel_read_file_id func) +{ + return false; +} +#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */ #endif /* _LINUX_IMA_H */ diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index 43109ef4d6bf..7f4a618fc8c1 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -208,7 +208,15 @@ kimage_validate_signature(struct kimage *image) return ret; } - return security_locked_down(LOCKDOWN_KEXEC); + /* If IMA is guaranteed to appraise a signature on the kexec + * image, permit it even if the kernel is otherwise locked + * down. + */ + if (!ima_appraise_signature(READING_KEXEC_IMAGE) && + security_locked_down(LOCKDOWN_KEXEC)) + return -EPERM; + + return 0; /* All other errors are fatal, including nomem, unparseable * signatures and signature check failures - even if signatures diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index ca10917b5f89..874bd77d3b91 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -111,6 +111,8 @@ struct ima_kexec_hdr { u64 count; }; +extern const int read_idmap[]; + #ifdef CONFIG_HAVE_IMA_KEXEC void ima_load_kexec_buffer(void); #else diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 1cffda4412b7..1747bc7bcb60 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -469,7 +469,7 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id) return 0; } -static const int read_idmap[READING_MAX_ID] = { +const int read_idmap[READING_MAX_ID] = { [READING_FIRMWARE] = FIRMWARE_CHECK, [READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK, [READING_MODULE] = MODULE_CHECK, diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 7b53f2ca58e2..b8773f05f9da 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -1339,3 +1339,53 @@ int ima_policy_show(struct seq_file *m, void *v) return 0; } #endif /* CONFIG_IMA_READ_POLICY */ + +#if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING) +/* + * ima_appraise_signature: whether IMA will appraise a given function using + * an IMA digital signature. This is restricted to cases where the kernel + * has a set of built-in trusted keys in order to avoid an attacker simply + * loading additional keys. + */ +bool ima_appraise_signature(enum kernel_read_file_id id) +{ + struct ima_rule_entry *entry; + bool found = false; + enum ima_hooks func; + + if (id >= READING_MAX_ID) + return false; + + func = read_idmap[id] ?: FILE_CHECK; + + rcu_read_lock(); + list_for_each_entry_rcu(entry, ima_rules, list) { + if (entry->action != APPRAISE) + continue; + + /* + * A generic entry will match, but otherwise require that it + * match the func we're looking for + */ + if (entry->func && entry->func != func) + continue; + + /* + * We require this to be a digital signature, not a raw IMA + * hash. + */ + if (entry->flags & IMA_DIGSIG_REQUIRED) + found = true; + + /* + * We've found a rule that matches, so break now even if it + * didn't require a digital signature - a later rule that does + * won't override it, so would be a false positive. + */ + break; + } + + rcu_read_unlock(); + return found; +} +#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */