From patchwork Mon Mar 18 19:51:39 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Garrett X-Patchwork-Id: 10858503 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7B3ED14DE for ; Mon, 18 Mar 2019 19:51:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 605532934B for ; Mon, 18 Mar 2019 19:51:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 545F228567; Mon, 18 Mar 2019 19:51:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, USER_IN_DEF_DKIM_WL autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B1E2628753 for ; Mon, 18 Mar 2019 19:51:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727298AbfCRTvx (ORCPT ); Mon, 18 Mar 2019 15:51:53 -0400 Received: from mail-pf1-f201.google.com ([209.85.210.201]:40730 "EHLO mail-pf1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727218AbfCRTvx (ORCPT ); Mon, 18 Mar 2019 15:51:53 -0400 Received: by mail-pf1-f201.google.com with SMTP id z26so14518137pfa.7 for ; Mon, 18 Mar 2019 12:51:52 -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=SXteoWL9bpeJoilHME4ZrwdnvwfbbMsRFl8oDKZhO7Q=; b=IFMunJOzoGUyo8PFNfqV3LotVDhDhlJw7qVhpAC06oqsAev6Mpsrjoej3tl4Wk+YhX YW0CsvWfKtqjXKFuGs6e2oqp+4z5HkN42bLCBq7XUNc5xlhiLNa8riknMta4YbYSLlVT DG8EH8xbFQXppsOgsG6yMyFkOmKwLcHEK6dqP5xzTefKyH4G+NPmvaTBiNsEGLC7pDoH hWbcDJleKgPJKeyHxxndMqpgviaTROxSNEc98Qnf9mHp3/LL0zUCm+l66DkmLdGkqgbE SOsy65WsP9soiZOUnFvWjsIJJzxWD0SQSsua7tF59MJ3/uQ2rip0Ui8v87WokIAJTHlZ uTlQ== 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=SXteoWL9bpeJoilHME4ZrwdnvwfbbMsRFl8oDKZhO7Q=; b=HRX20cIjP5yflVVi95Aoi6jmQbqWKVrfyNbKJf0mNWxTrhVe6rZ0wEolHwdhKj4mSP gJYsLGDMIYlPTf5MlENyPKhRDiMkFkBa7uxuuJq4tGp49YL9IiWJ83Pea6PJgwgvOwk1 /2ib6FU+f+9FT0vSZD3kS0xCz6tC5INGJfag06b575w3MB4w7SlTzVCJs73lx8doiDmH VZCt7AxoEE7m1DQ78qjalcCvHX0r0Gum1r/ma07yRrX7eWefTq0BcOKTAg06SI4xI+qc RWAsYClezA7ah0iTY/SDrhhMSEoDUsmEEWkt/2DSfORzFtk90Vq9j+NsYtV6JyG7K6f9 Rrfg== X-Gm-Message-State: APjAAAUimzd7az4nxKLWV59+UHfckyymF+QFBBANNd0C4A2YLZaT1kKv /X3Xho4gCKwlAw2GL8kvhhP4fgk2CgRI0GwEvvEsSNUXmmkTpsXf8CLhStbXLfkFPwu3xZZ2YVz YwUe5SoJe/IHGVyuDZ+FRSLEwCxZiMmVevPDQMqbe8InsBmO8x3IsOzW1S57dXMdsVUpsGJI0Ae nnD04fwkINxN9eXmiOLOU= X-Google-Smtp-Source: APXvYqxV/rya0JnPoSjAI8U40zz+MWcdA4T4ea78bKLObHj4dP7Ijgp6BtxjoNflOlTIB89Ae+7iK5jmaVtLiaiFKCYayg== X-Received: by 2002:a17:902:a60c:: with SMTP id u12mr6241391plq.114.1552938711985; Mon, 18 Mar 2019 12:51:51 -0700 (PDT) Date: Mon, 18 Mar 2019 12:51:39 -0700 In-Reply-To: <1552822761.8658.158.camel@linux.ibm.com> Message-Id: <20190318195139.111959-1-matthewgarrett@google.com> Mime-Version: 1.0 References: <1552822761.8658.158.camel@linux.ibm.com> X-Mailer: git-send-email 2.21.0.225.g810b269d1ac-goog Subject: [RFC] kexec: Allow kexec_file() with appropriate IMA policy when locked down From: Matthew Garrett To: linux-integrity@vger.kernel.org Cc: dhowells@redhat.com, zohar@linux.ibm.com, dmitry.kasatkin@gmail.com, kexec@lists.infradead.org, dyoung@redhat.com, ebiederm@xmission.com, Matthew Garrett , Matthew Garrett Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 --- include/linux/ima.h | 9 +++++ kernel/kexec_file.c | 9 +++-- security/integrity/ima/ima.h | 3 ++ security/integrity/ima/ima_main.c | 2 +- security/integrity/ima/ima_policy.c | 52 +++++++++++++++++++++++++++++ 5 files changed, 72 insertions(+), 3 deletions(-) diff --git a/include/linux/ima.h b/include/linux/ima.h index dc12fbcf484c..a78c04580a3c 100644 --- a/include/linux/ima.h +++ b/include/linux/ima.h @@ -132,4 +132,13 @@ 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_kexec_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 0cfe4f6f7f85..3598f93a731a 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -20,11 +20,11 @@ #include #include #include -#include #include #include #include #include +#include #include #include #include @@ -240,7 +240,12 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd, ret = 0; - if (kernel_is_locked_down(reason)) { + /* 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) && + kernel_is_locked_down(reason)) { ret = -EPERM; goto out; } diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index cc12f3449a72..93a6825bfcaf 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -20,6 +20,7 @@ #include #include #include +#include #include #include #include @@ -115,6 +116,8 @@ 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 357edd140c09..927fe889201a 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -473,7 +473,7 @@ 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 8bc8a1c8cb3f..bbd1d5b3d45a 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -21,6 +21,7 @@ #include #include #include +#include #include "ima.h" @@ -1336,4 +1337,55 @@ int ima_policy_show(struct seq_file *m, void *v) seq_puts(m, "\n"); 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 */