From: Eric Snowberg <eric.snowberg@xxxxxxxxxx> [ Upstream commit 56c5812623f95313f6a46fbf0beee7fa17c68bbf ] This fixes CVE-2020-26541. 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. Add 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. [DH: Made the following changes: - Added to have a config option to enable the facility. This allows a Kconfig solution to make sure that pkcs7_validate_trust() is enabled.[1][2] - Moved the functions out from the middle of the blacklist functions. - Added kerneldoc comments.] Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx> Signed-off-by: David Howells <dhowells@xxxxxxxxxx> Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> cc: Mickaël Salaün <mic@xxxxxxxxxxx> cc: Arnd Bergmann <arnd@xxxxxxxxxx> cc: keyrings@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20200901165143.10295-1-eric.snowberg@xxxxxxxxxx/ # rfc Link: https://lore.kernel.org/r/20200909172736.73003-1-eric.snowberg@xxxxxxxxxx/ # v2 Link: https://lore.kernel.org/r/20200911182230.62266-1-eric.snowberg@xxxxxxxxxx/ # v3 Link: https://lore.kernel.org/r/20200916004927.64276-1-eric.snowberg@xxxxxxxxxx/ # v4 Link: https://lore.kernel.org/r/20210122181054.32635-2-eric.snowberg@xxxxxxxxxx/ # v5 Link: https://lore.kernel.org/r/161428672051.677100.11064981943343605138.stgit@xxxxxxxxxxxxxxxxxxxxxx/ Link: https://lore.kernel.org/r/161433310942.902181.4901864302675874242.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2 Link: https://lore.kernel.org/r/161529605075.163428.14625520893961300757.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3 Link: https://lore.kernel.org/r/bc2c24e3-ed68-2521-0bf4-a1f6be4a895d@xxxxxxxxxxxxx/ [1] Link: https://lore.kernel.org/r/20210225125638.1841436-1-arnd@xxxxxxxxxx/ [2] Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- certs/Kconfig | 9 ++++ certs/blacklist.c | 43 +++++++++++++++++++ certs/blacklist.h | 2 + certs/system_keyring.c | 6 +++ include/keys/system_keyring.h | 15 +++++++ .../platform_certs/keyring_handler.c | 11 +++++ 6 files changed, 86 insertions(+) diff --git a/certs/Kconfig b/certs/Kconfig index c94e93d8bccf..76e469b56a77 100644 --- a/certs/Kconfig +++ b/certs/Kconfig @@ -83,4 +83,13 @@ config SYSTEM_BLACKLIST_HASH_LIST wrapper to incorporate the list into the kernel. Each <hash> should be a string of hex digits. +config SYSTEM_REVOCATION_LIST + bool "Provide system-wide ring of revocation certificates" + depends on SYSTEM_BLACKLIST_KEYRING + depends on PKCS7_MESSAGE_PARSER=y + help + If set, this allows revocation certificates to be stored in the + blacklist keyring and implements a hook whereby a PKCS#7 message can + be checked to see if it matches such a certificate. + endmenu diff --git a/certs/blacklist.c b/certs/blacklist.c index f1c434b04b5e..59b2f106b294 100644 --- a/certs/blacklist.c +++ b/certs/blacklist.c @@ -144,6 +144,49 @@ int is_binary_blacklisted(const u8 *hash, size_t hash_len) } EXPORT_SYMBOL_GPL(is_binary_blacklisted); +#ifdef CONFIG_SYSTEM_REVOCATION_LIST +/** + * add_key_to_revocation_list - Add a revocation certificate to the blacklist + * @data: The data blob containing the certificate + * @size: The size of data blob + */ +int add_key_to_revocation_list(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; +} + +/** + * is_key_on_revocation_list - Determine if the key for a PKCS#7 message is revoked + * @pkcs7: The PKCS#7 message to check + */ +int is_key_on_revocation_list(struct pkcs7_message *pkcs7) +{ + int ret; + + ret = pkcs7_validate_trust(pkcs7, blacklist_keyring); + + if (ret == 0) + return -EKEYREJECTED; + + return -ENOKEY; +} +#endif + /* * Initialise the blacklist */ diff --git a/certs/blacklist.h b/certs/blacklist.h index 1efd6fa0dc60..51b320cf8574 100644 --- a/certs/blacklist.h +++ b/certs/blacklist.h @@ -1,3 +1,5 @@ #include <linux/kernel.h> +#include <linux/errno.h> +#include <crypto/pkcs7.h> extern const char __initconst *const blacklist_hashes[]; diff --git a/certs/system_keyring.c b/certs/system_keyring.c index 798291177186..cc165b359ea3 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_on_revocation_list(pkcs7); + if (ret != -ENOKEY) { + pr_devel("PKCS#7 platform key is on revocation list\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..875e002a4180 100644 --- a/include/keys/system_keyring.h +++ b/include/keys/system_keyring.h @@ -31,6 +31,7 @@ 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 is_hash_blacklisted(const u8 *hash, size_t hash_len, @@ -49,6 +50,20 @@ static inline int is_binary_blacklisted(const u8 *hash, size_t hash_len) } #endif +#ifdef CONFIG_SYSTEM_REVOCATION_LIST +extern int add_key_to_revocation_list(const char *data, size_t size); +extern int is_key_on_revocation_list(struct pkcs7_message *pkcs7); +#else +static inline int add_key_to_revocation_list(const char *data, size_t size) +{ + return 0; +} +static inline int is_key_on_revocation_list(struct pkcs7_message *pkcs7) +{ + return -ENOKEY; +} +#endif + #ifdef CONFIG_IMA_BLACKLIST_KEYRING extern struct key *ima_blacklist_keyring; diff --git a/security/integrity/platform_certs/keyring_handler.c b/security/integrity/platform_certs/keyring_handler.c index c5ba695c10e3..5604bd57c990 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); } +/* + * Add an X509 cert to the revocation list. + */ +static __init void uefi_revocation_list_x509(const char *source, + const void *data, size_t len) +{ + add_key_to_revocation_list(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_revocation_list_x509; return 0; } -- 2.30.2
