From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D21CC43381 for ; Wed, 13 Mar 2019 11:58:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B15B2171F for ; Wed, 13 Mar 2019 11:58:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726130AbfCML64 (ORCPT ); Wed, 13 Mar 2019 07:58:56 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:43580 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725876AbfCML64 (ORCPT ); Wed, 13 Mar 2019 07:58:56 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x2DBt4rI109252 for ; Wed, 13 Mar 2019 07:58:55 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2r70vmhuj4-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 13 Mar 2019 07:58:54 -0400 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 13 Mar 2019 11:58:49 -0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x2DBwmY550528268 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 13 Mar 2019 11:58:48 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 472DEAE063; Wed, 13 Mar 2019 11:58:48 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 864ABAE045; Wed, 13 Mar 2019 11:58:47 +0000 (GMT) Received: from localhost.localdomain (unknown [9.80.93.217]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 13 Mar 2019 11:58:47 +0000 (GMT) Subject: Re: [RFC] kexec: Allow kexec_file() with appropriate IMA policy when locked down From: Mimi Zohar To: Matthew Garrett , linux-integrity@vger.kernel.org Cc: dhowells@redhat.com, dmitry.kasatkin@gmail.com, Matthew Garrett Date: Wed, 13 Mar 2019 07:58:36 -0400 In-Reply-To: <20190312195715.101995-1-matthewgarrett@google.com> References: <20190312195715.101995-1-matthewgarrett@google.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 (3.20.5-1.fc24) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19031311-0016-0000-0000-000002615C6E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19031311-0017-0000-0000-000032BC0909 Message-Id: <1552478316.24794.210.camel@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-13_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903130087 Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Tue, 2019-03-12 at 12:57 -0700, Matthew Garrett wrote: > 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 instead, either with native IMA digital > signatures or EVM-protected IMA hashes. Add a function to determine > whether IMA will verify signatures on kexec files, 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. Thank you for working on this!  With the changes suggested below, it might work.  :) > > Signed-off-by: Matthew Garrett > --- > include/linux/evm.h | 6 +++++ > include/linux/ima.h | 9 ++++++++ > kernel/kexec_file.c | 9 ++++++-- > security/integrity/evm/evm_main.c | 2 +- > security/integrity/ima/ima_policy.c | 35 +++++++++++++++++++++++++++++ > 5 files changed, 58 insertions(+), 3 deletions(-) > > diff --git a/include/linux/evm.h b/include/linux/evm.h > index 8302bc29bb35..6e89d046b716 100644 > --- a/include/linux/evm.h > +++ b/include/linux/evm.h > @@ -15,6 +15,7 @@ > struct integrity_iint_cache; > > #ifdef CONFIG_EVM > +extern bool evm_key_loaded(void); > extern int evm_set_key(void *key, size_t keylen); > extern enum integrity_status evm_verifyxattr(struct dentry *dentry, > const char *xattr_name, > @@ -45,6 +46,11 @@ static inline int posix_xattr_acl(const char *xattrname) > #endif > #else > > +static inline bool evm_key_loaded(void) > +{ > + return false; > +} > + > static inline int evm_set_key(void *key, size_t keylen) > { > return -EOPNOTSUPP; > diff --git a/include/linux/ima.h b/include/linux/ima.h > index dc12fbcf484c..2ec593537c9b 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_kexec_signature(void); > +#else > +static inline bool ima_appraise_kexec_signature(void) > +{ > + 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..8ca607f1b515 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_kexec_signature() && > + kernel_is_locked_down(reason)) { > ret = -EPERM; > goto out; > } > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c > index b6d9f14bc234..aad61bc0f774 100644 > --- a/security/integrity/evm/evm_main.c > +++ b/security/integrity/evm/evm_main.c > @@ -87,7 +87,7 @@ static void __init evm_init_config(void) > pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs); > } > > -static bool evm_key_loaded(void) > +bool evm_key_loaded(void) > { > return (bool)(evm_initialized & EVM_KEY_MASK); > } This might be sufficient for your environment, but in general it isn't. > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c > index 8bc8a1c8cb3f..c06b1a6b3528 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 +1337,38 @@ 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) With these defines, the function isn't limited to just "lockdown".  Either fix the defines or the patch description. > +/* > + * ima_appraise_kexec: whether IMA will appraise a kexec image, either via > + * IMA digital signatures or with a hash and EVM validation > + */ > +bool ima_appraise_kexec_signature(void) Instead of making this specific to kexec, how about naming the function something like ima_require_appraise_signature() and pass the kernel_read_file_id (eg. READING_KEXEC_IMAGE, READING_MODULE). > +{ > + struct ima_rule_entry *entry; > + bool found = false; > + > + rcu_read_lock(); > + list_for_each_entry_rcu(entry, ima_rules, list) { > + if (entry->func != KEXEC_KERNEL_CHECK || > + entry->action != APPRAISE) > + continue; > + > + /* > + * We require this to be a digital signature, not a raw IMA > + * hash. An IMA hash is acceptable as long as it's covered > + * by an EVM signature. > + */ > + if (entry->flags & IMA_DIGSIG_REQUIRED || > + evm_key_loaded()) { evm_key_loaded() is a problem. > + found = true; > + break; > + } The first matching rule dictates the policy.  Move the "break" here. Walking the list looking for a specific rule might not be a true indication of the policy.  For example, with a generic rule prior to a specific rule, the generic rule might take precedence. As long as the generic rules require a signature, there isn't a problem.  I would stop walking the policy rules after the first "appraise" rule that doesn't require a signature.  This will prevent returning a false positive. The builtin and arch policy rules are by design forced to be first. Mimi > + } > + > + rcu_read_unlock(); > + return found; > +} > +#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */