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    Subject[PATCH 5.10 097/101] certs: Add EFI_CERT_X509_GUID support for dbx entries
    Date
    From: Eric Snowberg <eric.snowberg@oracle.com>

    [ 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@oracle.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
    cc: Randy Dunlap <rdunlap@infradead.org>
    cc: Mickaël Salaün <mic@digikod.net>
    cc: Arnd Bergmann <arnd@kernel.org>
    cc: keyrings@vger.kernel.org
    Link: https://lore.kernel.org/r/20200901165143.10295-1-eric.snowberg@oracle.com/ # rfc
    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/20210122181054.32635-2-eric.snowberg@oracle.com/ # v5
    Link: https://lore.kernel.org/r/161428672051.677100.11064981943343605138.stgit@warthog.procyon.org.uk/
    Link: https://lore.kernel.org/r/161433310942.902181.4901864302675874242.stgit@warthog.procyon.org.uk/ # v2
    Link: https://lore.kernel.org/r/161529605075.163428.14625520893961300757.stgit@warthog.procyon.org.uk/ # v3
    Link: https://lore.kernel.org/r/bc2c24e3-ed68-2521-0bf4-a1f6be4a895d@infradead.org/ [1]
    Link: https://lore.kernel.org/r/20210225125638.1841436-1-arnd@kernel.org/ [2]
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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
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