From patchwork Wed Jul 31 22:16:13 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Garrett X-Patchwork-Id: 11069655 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 EA6B813A4 for ; Wed, 31 Jul 2019 22:17:34 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DAFE427F17 for ; Wed, 31 Jul 2019 22:17:34 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CF19327F81; Wed, 31 Jul 2019 22:17:34 +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=-14.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 491A627F17 for ; Wed, 31 Jul 2019 22:17:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731397AbfGaWRc (ORCPT ); Wed, 31 Jul 2019 18:17:32 -0400 Received: from mail-pf1-f202.google.com ([209.85.210.202]:38867 "EHLO mail-pf1-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731396AbfGaWRb (ORCPT ); Wed, 31 Jul 2019 18:17:31 -0400 Received: by mail-pf1-f202.google.com with SMTP id e25so44214466pfn.5 for ; Wed, 31 Jul 2019 15:17:30 -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=Ogy4z5xXdkGcZVx/gotBD44dFgIvUZxytASg1dmnrz4=; b=Bajk5gYeO0raa2iJAXLUTeo1rNux2thWTyxy5cP2BZX9rVUFcLLwBM1Ihyr4IW6Uxu OVe2hKqMjonh2PlJah6B/xRvCxOEBYAVBGbGtG5SxGXbvgbox/ljX9f23uTjmk8CdtHj OpACdBgg8QTDRBPMzNVaG3NusYWPWtzuSDBMG1K3yU06iS9f0IVwyo5+DUjxp1ZaqLKn 2PqUsKDMn3y2VNU/ELITmp+dzRb2ku3sU7bSFIAZC3m3mAJLzfVbP0Edc+IQpH/qk47X 2UowsAKC5Wju2BwdPCp4ZZhOFCQRE0tSdOQOXnHroYpPv2eDlt8O+buvUZBVcS1GIREQ Qz/w== 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=Ogy4z5xXdkGcZVx/gotBD44dFgIvUZxytASg1dmnrz4=; b=IIUG9SDEPjSqPRIs3QCLTg+UQUVggc64IkvPpWWaLuFlRFiipF/9EflF59QUP+cuVa 25BkgbuL8ZLi31gfumc7ttrBVoLKwOrmKGYi2QJkvGv6/qJMhXlU7fZcb7UqZGBtNAL4 2Auf6qi0d1Kb5k77udSX+VnbIdHclsuCiV5yzt22nOfVYOguou5i60yuRC46tEnwgR4R UDmaq9gEfJBwVP1JOqHr+EwvFax9sF83Wa/ZfAkwQP8fhwzIOvAnGL8AT3tOCccFma21 XxZ0lIc9FPb99l1UcV+HjItZq+vU/Q4xIgRwYn9WSfRXmr5RY5Kz8VJ5piU7MWOdpsd7 Tdkw== X-Gm-Message-State: APjAAAVnnh+s2RBmW4C96ABb4ispdf8cO3VDVZQmTBO6JWO8GPZ/yB2d KDgsyIHmg64vwg2Ke2pWvZMEJZ9gEp8YJgyIaMJorw== X-Google-Smtp-Source: APXvYqxZSsn4zOtqAMIbC8IIUJ8BgotlRvfyfmjrcz+Kzfba+ryUsIe0e+54iON0Ue9ORs3wFILRx4yWxTev9k6Xexi4Gg== X-Received: by 2002:a63:6c7:: with SMTP id 190mr114475501pgg.7.1564611450073; Wed, 31 Jul 2019 15:17:30 -0700 (PDT) Date: Wed, 31 Jul 2019 15:16:13 -0700 In-Reply-To: <20190731221617.234725-1-matthewgarrett@google.com> Message-Id: <20190731221617.234725-26-matthewgarrett@google.com> Mime-Version: 1.0 References: <20190731221617.234725-1-matthewgarrett@google.com> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog Subject: [PATCH V37 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: 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 Acked-by: Mimi Zohar Cc: Dmitry Kasatkin Cc: linux-integrity@vger.kernel.org --- include/linux/ima.h | 9 ++++++ kernel/kexec_file.c | 12 +++++-- security/integrity/ima/ima.h | 2 ++ security/integrity/ima/ima_main.c | 2 +- security/integrity/ima/ima_policy.c | 50 +++++++++++++++++++++++++++++ 5 files changed, 72 insertions(+), 3 deletions(-) diff --git a/include/linux/ima.h b/include/linux/ima.h index a20ad398d260..1c37f17f7203 100644 --- a/include/linux/ima.h +++ b/include/linux/ima.h @@ -131,4 +131,13 @@ 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 dd06f1070d66..13c9960a5860 100644 --- a/kernel/kexec_file.c +++ b/kernel/kexec_file.c @@ -228,9 +228,17 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd, goto out; } - ret = security_locked_down(LOCKDOWN_KEXEC); - if (ret) + ret = 0; + + /* 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)) { + ret = -EPERM; goto out; + } break; diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h index 011b91c79351..64dcb11cf444 100644 --- a/security/integrity/ima/ima.h +++ b/security/integrity/ima/ima.h @@ -113,6 +113,8 @@ 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 584019728660..b9f57503af2c 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -502,7 +502,7 @@ 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 6df7f641ff66..827f1e33fe86 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -1456,3 +1456,53 @@ 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 */