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

[Jarkko Sakkinen]

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 ...".

> ---
>  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.

/Jarkko