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    SubjectRe: [PATCH v5 1/4] certs: Add EFI_CERT_X509_GUID support for dbx entries
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    > On Jan 27, 2021, at 8:54 PM, Nayna <nayna@linux.vnet.ibm.com> wrote:
    >
    >
    > On 1/22/21 1:10 PM, Eric Snowberg wrote:
    >> 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.
    >>
    >> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
    >> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    >> Signed-off-by: David Howells <dhowells@redhat.com>
    >> ---
    >> v5: Function name changes done by David Howells
    >> ---
    >> certs/blacklist.c | 32 +++++++++++++++++++
    >> certs/blacklist.h | 12 +++++++
    >> certs/system_keyring.c | 6 ++++
    >> include/keys/system_keyring.h | 11 +++++++
    >> .../platform_certs/keyring_handler.c | 11 +++++++
    >> 5 files changed, 72 insertions(+)
    >>
    >> diff --git a/certs/blacklist.c b/certs/blacklist.c
    >> index 6514f9ebc943..a7f021878a4b 100644
    >> --- a/certs/blacklist.c
    >> +++ b/certs/blacklist.c
    >> @@ -100,6 +100,38 @@ int mark_hash_blacklisted(const char *hash)
    >> return 0;
    >> }
    >>
    >> +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;
    >> +}
    >> +
    >> +int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
    >> +{
    >> + int ret;
    >> +
    >> + ret = validate_trust(pkcs7, blacklist_keyring);
    >> +
    >> + if (ret == 0)
    >> + return -EKEYREJECTED;
    >> +
    >> + return -ENOKEY;
    >> +}
    >> +
    >> /**
    >> * is_hash_blacklisted - Determine if a hash is blacklisted
    >> * @hash: The hash to be checked as a binary blob
    >> diff --git a/certs/blacklist.h b/certs/blacklist.h
    >> index 1efd6fa0dc60..420bb7c86e07 100644
    >> --- a/certs/blacklist.h
    >> +++ b/certs/blacklist.h
    >> @@ -1,3 +1,15 @@
    >> #include <linux/kernel.h>
    >> +#include <linux/errno.h>
    >> +#include <crypto/pkcs7.h>
    >>
    >> extern const char __initconst *const blacklist_hashes[];
    >> +
    >> +#ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
    >> +#define validate_trust pkcs7_validate_trust
    >> +#else
    >> +static inline int validate_trust(struct pkcs7_message *pkcs7,
    >> + struct key *trust_keyring)
    >> +{
    >> + return -ENOKEY;
    >> +}
    >> +#endif
    >> 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..61f98739e8b1 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 add_key_to_revocation_list(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_on_revocation_list(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 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
    >> 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);
    >> +}
    >
    > In keeping the naming convention with other functions that blacklist hashes, why can't we call these functions:
    >
    > * uefi_revocation_list_x509() -> uefi_blacklist_x509_cert()
    > * add_key_to_revocation_list() -> uefi_blacklist_cert()
    > * is_key_on_revocation_list() -> is_cert_blacklisted()

    The word revocation was used do to the updated Linux coding style:

    https://lkml.org/lkml/2020/7/4/229


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