Re: [RFC PATCH] certs: Add EFI_CERT_X509_GUID support for dbx entries]

[Eric Snowberg]

> On Sep 4, 2020, at 6:59 AM, Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> 
> On Tue, Sep 01, 2020 at 12:51:43PM -0400, Eric Snowberg wrote:
>> The Secure Boot Forbidden Signature Database, dbx, contains a list of now
>> revoked signatures and keys previously approved to boot with UEFI Secure
>> Boot enabled.  The dbx is capable of containing any number of
>> EFI_CERT_X509_SHA256_GUID, EFI_CERT_SHA256_GUID, and EFI_CERT_X509_GUID
>> entries.
>> 
>> Currently when EFI_CERT_X509_GUID are contained in the dbx, the entries are
>> skipped.
>> 
>> This change adds support for EFI_CERT_X509_GUID dbx entries. When a
>> EFI_CERT_X509_GUID is found, it is added as an asymmetrical key to the
>> .blacklist keyring.  Anytime the .platform keyring is used, the keys in
>> the .blacklist keyring are referenced, if a matching key is found, the
>> key will be rejected.
>> 
>> Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
> 
> In the last paragraph, please use imperative form: "Add support for …".

I will change this in V2.

> 
>> ---
>> certs/blacklist.c                             | 36 +++++++++++++++++++
>> certs/system_keyring.c                        |  6 ++++
>> include/keys/system_keyring.h                 | 11 ++++++
>> .../platform_certs/keyring_handler.c          | 11 ++++++
>> 4 files changed, 64 insertions(+)
>> 
>> diff --git a/certs/blacklist.c b/certs/blacklist.c
>> index 6514f9ebc943..17ebf50cf0ae 100644
>> --- a/certs/blacklist.c
>> +++ b/certs/blacklist.c
>> @@ -15,6 +15,7 @@
>> #include <linux/err.h>
>> #include <linux/seq_file.h>
>> #include <keys/system_keyring.h>
>> +#include <crypto/pkcs7.h>
>> #include "blacklist.h"
>> 
>> static struct key *blacklist_keyring;
>> @@ -100,6 +101,41 @@ int mark_hash_blacklisted(const char *hash)
>> 	return 0;
>> }
>> 
>> +int mark_key_revocationlisted(const char *data, size_t size)
>> +{
>> +	key_ref_t key;
>> +
>> +	key = key_create_or_update(make_key_ref(blacklist_keyring, true),
>> +				   "asymmetric",
>> +				   NULL,
>> +				   data,
>> +				   size,
>> +				   ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
>> +				    KEY_USR_VIEW),
>> +				   KEY_ALLOC_NOT_IN_QUOTA |
>> +				   KEY_ALLOC_BUILT_IN);
>> +
>> +	if (IS_ERR(key)) {
>> +		pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key));
>> +		return PTR_ERR(key);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +int is_key_revocationlisted(struct pkcs7_message *pkcs7)
>> +{
>> +	int ret;
>> +
>> +	ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
>> +
>> +	if (ret == 0)
>> +		return -EKEYREJECTED;
>> +
>> +	return -ENOKEY;
>> +}
>> +EXPORT_SYMBOL_GPL(is_key_revocationlisted);
>> +
>> /**
>>  * is_hash_blacklisted - Determine if a hash is blacklisted
>>  * @hash: The hash to be checked as a binary blob
>> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
>> index 798291177186..f8ea96219155 100644
>> --- a/certs/system_keyring.c
>> +++ b/certs/system_keyring.c
>> @@ -241,6 +241,12 @@ int verify_pkcs7_message_sig(const void *data, size_t len,
>> 			pr_devel("PKCS#7 platform keyring is not available\n");
>> 			goto error;
>> 		}
>> +
>> +		ret = is_key_revocationlisted(pkcs7);
>> +		if (ret != -ENOKEY) {
>> +			pr_devel("PKCS#7 platform key revocationlisted\n");
>> +			goto error;
>> +		}
>> 	}
>> 	ret = pkcs7_validate_trust(pkcs7, trusted_keys);
>> 	if (ret < 0) {
>> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
>> index fb8b07daa9d1..b6991cfe1b6d 100644
>> --- a/include/keys/system_keyring.h
>> +++ b/include/keys/system_keyring.h
>> @@ -31,11 +31,14 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
>> #define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
>> #endif
>> 
>> +extern struct pkcs7_message *pkcs7;
>> #ifdef CONFIG_SYSTEM_BLACKLIST_KEYRING
>> extern int mark_hash_blacklisted(const char *hash);
>> +extern int mark_key_revocationlisted(const char *data, size_t size);
>> extern int is_hash_blacklisted(const u8 *hash, size_t hash_len,
>> 			       const char *type);
>> extern int is_binary_blacklisted(const u8 *hash, size_t hash_len);
>> +extern int is_key_revocationlisted(struct pkcs7_message *pkcs7);
>> #else
>> static inline int is_hash_blacklisted(const u8 *hash, size_t hash_len,
>> 				      const char *type)
>> @@ -47,6 +50,14 @@ static inline int is_binary_blacklisted(const u8 *hash, size_t hash_len)
>> {
>> 	return 0;
>> }
>> +static inline int mark_key_revocationlisted(const char *data, size_t size)
>> +{
>> +	return 0;
>> +}
>> +static inline int is_key_revocationlisted(struct pkcs7_message *pkcs7)
>> +{
>> +	return -ENOKEY;
>> +}
>> #endif
>> 
>> #ifdef CONFIG_IMA_BLACKLIST_KEYRING
>> diff --git a/security/integrity/platform_certs/keyring_handler.c b/security/integrity/platform_certs/keyring_handler.c
>> index c5ba695c10e3..cc5a43804bc4 100644
>> --- a/security/integrity/platform_certs/keyring_handler.c
>> +++ b/security/integrity/platform_certs/keyring_handler.c
>> @@ -55,6 +55,15 @@ static __init void uefi_blacklist_binary(const char *source,
>> 	uefi_blacklist_hash(source, data, len, "bin:", 4);
>> }
>> 
>> +/*
>> + * Revocationlist the X509 cert
>> + */
>> +static __init void uefi_revocationlist_x509(const char *source,
>> +					    const void *data, size_t len)
>> +{
>> +	mark_key_revocationlisted(data, len);
>> +}
>> +
>> /*
>>  * Return the appropriate handler for particular signature list types found in
>>  * the UEFI db and MokListRT tables.
>> @@ -76,5 +85,7 @@ __init efi_element_handler_t get_handler_for_dbx(const efi_guid_t *sig_type)
>> 		return uefi_blacklist_x509_tbs;
>> 	if (efi_guidcmp(*sig_type, efi_cert_sha256_guid) == 0)
>> 		return uefi_blacklist_binary;
>> +	if (efi_guidcmp(*sig_type, efi_cert_x509_guid) == 0)
>> +		return uefi_revocationlist_x509;
>> 	return 0;
>> }
>> -- 
>> 2.18.1
>> 
> 
> I did not find anything wrong with the code change.

Thanks