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From: Eric Snowberg <eric.snowberg@oracle.com>
To: keyrings@vger.kernel.org, linux-integrity@vger.kernel.org,
	zohar@linux.ibm.com, dhowells@redhat.com, dwmw2@infradead.org,
	herbert@gondor.apana.org.au, davem@davemloft.net,
	jarkko@kernel.org, jmorris@namei.org, serge@hallyn.com
Cc: eric.snowberg@oracle.com, keescook@chromium.org,
	gregkh@linuxfoundation.org, torvalds@linux-foundation.org,
	scott.branden@broadcom.com, weiyongjun1@huawei.com,
	nayna@linux.ibm.com, ebiggers@google.com, ardb@kernel.org,
	nramas@linux.microsoft.com, lszubowi@redhat.com,
	linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	James.Bottomley@HansenPartnership.com, pjones@redhat.com,
	konrad.wilk@oracle.com
Subject: [PATCH v5 11/12] integrity: Trust MOK keys if MokListTrustedRT found
Date: Tue,  7 Sep 2021 12:01:09 -0400	[thread overview]
Message-ID: <20210907160110.2699645-12-eric.snowberg@oracle.com> (raw)
In-Reply-To: <20210907160110.2699645-1-eric.snowberg@oracle.com>

A new Machine Owner Key (MOK) variable called MokListTrustedRT has been
introduced in shim. When this UEFI variable is set, it indicates the
end-user has made the decision themself that they wish to trust MOK keys
within the Linux trust boundary.  It is not an error if this variable
does not exist. If it does not exist, the MOK keys should not be trusted
within the kernel.

MOK variables are mirrored from Boot Services to Runtime Services.  When
shim sees the new MokTML BS variable, it will create a new variable
(before Exit Boot Services is called) called MokListTrustedRT without
EFI_VARIABLE_NON_VOLATILE set.  Following Exit Boot Services, UEFI
variables can only be set and created with SetVariable if both
EFI_VARIABLE_RUNTIME_ACCESS & EFI_VARIABLE_NON_VOLATILE are set.
Therefore, this can not be defeated by simply creating a
MokListTrustedRT variable from Linux, the existence of
EFI_VARIABLE_NON_VOLATILE will cause uefi_check_trust_machine_keys to
return false.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
---
v1: Initial version
v2: Removed mok_keyring_trust_setup function
v4: Unmodified from v2
v5: Rename to machine keyring
---
 .../platform_certs/machine_keyring.c          | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/security/integrity/platform_certs/machine_keyring.c b/security/integrity/platform_certs/machine_keyring.c
index 948ec6c738c8..635ab2b9e289 100644
--- a/security/integrity/platform_certs/machine_keyring.c
+++ b/security/integrity/platform_certs/machine_keyring.c
@@ -5,6 +5,7 @@
  * Copyright (c) 2021, Oracle and/or its affiliates.
  */
 
+#include <linux/efi.h>
 #include "../integrity.h"
 
 static __init int machine_keyring_init(void)
@@ -40,3 +41,29 @@ void __init add_to_machine_keyring(const char *source, const void *data, size_t
 	if (rc)
 		pr_info("Error adding keys to machine keyring %s\n", source);
 }
+
+/*
+ * Try to load the MokListTrustedRT UEFI variable to see if we should trust
+ * the mok keys within the kernel. It is not an error if this variable
+ * does not exist.  If it does not exist, mok keys should not be trusted
+ * within the machine keyring.
+ */
+static __init bool uefi_check_trust_mok_keys(void)
+{
+	efi_status_t status;
+	unsigned int mtrust = 0;
+	unsigned long size = sizeof(mtrust);
+	efi_guid_t guid = EFI_SHIM_LOCK_GUID;
+	u32 attr;
+
+	status = efi.get_variable(L"MokListTrustedRT", &guid, &attr, &size, &mtrust);
+
+	/*
+	 * The EFI_VARIABLE_NON_VOLATILE check is to verify MokListTrustedRT
+	 * was set thru shim mirrioring and not by a user from the host os.
+	 * According to the UEFI spec, once EBS is performed, SetVariable()
+	 * will succeed only when both EFI_VARIABLE_RUNTIME_ACCESS &
+	 * EFI_VARIABLE_NON_VOLATILE are set.
+	 */
+	return (status == EFI_SUCCESS && (!(attr & EFI_VARIABLE_NON_VOLATILE)));
+}
-- 
2.18.4


  parent reply	other threads:[~2021-09-07 16:03 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-07 16:00 [PATCH v5 00/12] Enroll kernel keys thru MOK Eric Snowberg
2021-09-07 16:00 ` [PATCH v5 01/12] integrity: Introduce a Linux keyring called machine Eric Snowberg
2021-09-09 13:55   ` Jarkko Sakkinen
2021-09-09 15:19   ` Mimi Zohar
2021-09-09 17:32     ` Eric Snowberg
2021-09-07 16:01 ` [PATCH v5 02/12] integrity: Do not allow machine keyring updates following init Eric Snowberg
2021-09-09 13:43   ` Jarkko Sakkinen
2021-09-07 16:01 ` [PATCH v5 03/12] KEYS: CA link restriction Eric Snowberg
2021-09-07 16:01 ` [PATCH v5 04/12] integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca Eric Snowberg
2021-09-09 13:49   ` Jarkko Sakkinen
2021-09-09 17:25   ` Mimi Zohar
2021-09-09 17:53     ` Eric Snowberg
2021-09-09 18:19       ` Mimi Zohar
2021-09-07 16:01 ` [PATCH v5 05/12] integrity: add new keyring handler for mok keys Eric Snowberg
2021-09-07 16:01 ` [PATCH v5 06/12] KEYS: add a reference to machine keyring Eric Snowberg
2021-09-07 16:01 ` [PATCH v5 07/12] KEYS: Introduce link restriction to include builtin, secondary and machine keys Eric Snowberg
2021-09-09 17:26   ` Mimi Zohar
2021-09-09 18:03     ` Eric Snowberg
2021-09-09 18:19       ` Mimi Zohar
2021-09-07 16:01 ` [PATCH v5 08/12] KEYS: integrity: change link restriction to trust the machine keyring Eric Snowberg
2021-09-09 17:27   ` Mimi Zohar
2021-09-07 16:01 ` [PATCH v5 09/12] KEYS: link secondary_trusted_keys to machine trusted keys Eric Snowberg
2021-09-07 16:01 ` [PATCH v5 10/12] integrity: store reference to machine keyring Eric Snowberg
2021-09-07 16:01 ` Eric Snowberg [this message]
2021-09-07 16:01 ` [PATCH v5 12/12] integrity: Only use machine keyring when uefi_check_trust_mok_keys is true Eric Snowberg
2021-09-09 13:58   ` Jarkko Sakkinen
2021-09-08 16:03 ` [PATCH v5 00/12] Enroll kernel keys thru MOK Jarkko Sakkinen
2021-09-08 16:49   ` Jarkko Sakkinen
2021-09-08 22:25     ` Eric Snowberg
2021-09-09 13:02       ` Mimi Zohar
2021-09-08 17:09   ` Eric Snowberg

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