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.snowb...@oracle.com>
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
