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[209.132.180.67]) by mx.google.com with ESMTP id r14si37165274pli.257.2019.08.07.17.09.55; Wed, 07 Aug 2019 17:10:10 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=IzoA99Ev; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389760AbfHHAIy (ORCPT + 99 others); Wed, 7 Aug 2019 20:08:54 -0400 Received: from mail-pf1-f201.google.com ([209.85.210.201]:45294 "EHLO mail-pf1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389756AbfHHAIa (ORCPT ); Wed, 7 Aug 2019 20:08:30 -0400 Received: by mail-pf1-f201.google.com with SMTP id i27so57847017pfk.12 for ; Wed, 07 Aug 2019 17:08:29 -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=IzoA99EvVVMGm9iXr5KRRBbeK85e/Ze+iJ9iWUhTulS6b8deHVOQEYewHyfCg3YWKb 3n9ZeQ8b9FstJivLxoyemYdyRzOeASPo7Lb9s6Lul+7rnh/0DUQLnMQerlb9jVwlmAuX CWb1WrhDxYczCeXgOokUhcIjn90LF2+4iaeQpYsBF7vvqj61khqLVsfX5AIHVy59Bfku Cqar1nW/4zmvbfZHpnDPUl8up88QpGSd2JhrKka8MnIZKA43SrVLBO8QNH40/SRdST3C o9GdZ0A7xwSwZT23wwAu1n/eRvupnqUT4xYpFjmhWFyV9vQuQWlJuWMKfIIU76DxdSxp fgmA== 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=mtCgnyR6MJ2Jdp72/LHID5uvPCcQw4CQ5DMzQqIE3s3Fco+l6fBc5drq+9YGsj25GT 4nT6mqFNLZzu2teYGBU4eespDyTEDPZMPnkWVVQoVrKVOp06pOG4pQ6tP7y7szoyZ4u4 YBcVbfOH71s8w2ui2vyD1QmHsEuPKpxxncubna8xaQPrzrCVqHOgxpzlszrqSAZNaZOb WnY6mEaFXCE9i/zPNXAD65H0/SZ3TyuJMdx5JzJ7BIc4pH6pQFky7MEbWw51fDgrwrTD 4xDX4qLkwGBHW5+vu3vgop37Rgu3OTaOeP8FcTrK8SuescKQoLqIMRDb+v5oFzBgfazC Qkzg== X-Gm-Message-State: APjAAAV6it7CCeLNIFBIZe75Twq5+Z/f6rbVg9gW/6NQIAeS8rxfp2vG WtFctL7dX1hOUXKOHvC2GWhJ3IASUO0GyYUSlX3F2g== X-Received: by 2002:a63:4522:: with SMTP id s34mr9957055pga.362.1565222909034; Wed, 07 Aug 2019 17:08:29 -0700 (PDT) Date: Wed, 7 Aug 2019 17:07:17 -0700 In-Reply-To: <20190808000721.124691-1-matthewgarrett@google.com> Message-Id: <20190808000721.124691-26-matthewgarrett@google.com> Mime-Version: 1.0 References: <20190808000721.124691-1-matthewgarrett@google.com> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog Subject: [PATCH V38 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 */ -- 2.22.0.770.g0f2c4a37fd-goog