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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 1/4] certs: Add EFI_CERT_X509_GUID support for dbx entries From: David Howells To: Eric Snowberg Cc: Jarkko Sakkinen , Randy Dunlap , =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Arnd Bergmann , keyrings@vger.kernel.org, dhowells@redhat.com, Jarkko Sakkinen , =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 25 Feb 2021 20:58:40 +0000 Message-ID: <161428672051.677100.11064981943343605138.stgit@warthog.procyon.org.uk> In-Reply-To: <161428671215.677100.6372209948022011988.stgit@warthog.procyon.org.uk> References: <161428671215.677100.6372209948022011988.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Snowberg 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. - Moved the functions out from the middle of the blacklist functions. - Added kerneldoc comments.] Signed-off-by: Eric Snowberg Signed-off-by: David Howells cc: Jarkko Sakkinen cc: Randy Dunlap cc: Mickaël Salaün cc: Arnd Bergmann cc: keyrings@vger.kernel.org Link: https://lore.kernel.org/r/20200901165143.10295-1-eric.snowberg@oracle.com/ Link: https://lore.kernel.org/r/20200909172736.73003-1-eric.snowberg@oracle.com/ # v2 Link: https://lore.kernel.org/r/20200911182230.62266-1-eric.snowberg@oracle.com/ # v3 Link: https://lore.kernel.org/r/20200916004927.64276-1-eric.snowberg@oracle.com/ # v4 Link: https://lore.kernel.org/r/2660556.1610545213@warthog.procyon.org.uk/ Link: https://lore.kernel.org/r/20210122181054.32635-2-eric.snowberg@oracle.com/ # v5 Link: https://lore.kernel.org/r/bc2c24e3-ed68-2521-0bf4-a1f6be4a895d@infradead.org/ Link: https://lore.kernel.org/r/20210225125638.1841436-1-arnd@kernel.org/ --- certs/Kconfig | 9 ++++ certs/blacklist.c | 43 ++++++++++++++++++++ certs/blacklist.h | 2 + certs/system_keyring.c | 6 +++ include/keys/system_keyring.h | 15 +++++++ .../integrity/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 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 bffe4c6f4a9e..2b8644123d5f 100644 --- a/certs/blacklist.c +++ b/certs/blacklist.c @@ -145,6 +145,49 @@ 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 +#include +#include extern const char __initconst *const blacklist_hashes[]; diff --git a/certs/system_keyring.c b/certs/system_keyring.c index 4b693da488f1..ed98754d5795 100644 --- a/certs/system_keyring.c +++ b/certs/system_keyring.c @@ -242,6 +242,12 @@ 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; }