Instead of calculating a regular file hash and verifying the signature stored in the 'security.ima' xattr against the calculated file hash, get fs-verity's file digest and verify the signature (version 3) stored in 'security.ima' against the digest. The policy rule 'appraise_type=' option is extended to support 'sigv3', which is initiality limited to fs-verity. The fs-verity 'appraise' rules are identified by the 'digest-type=verity' option and require the 'appraise_type=sigv3' option. The following 'appraise' policy rule requires fsverity file digests. (The rule may be constrained, for example based on a fsuuid or LSM label.) Basic fs-verity policy rule example: appraise func=BPRM_CHECK digest_type=verity appraise_type=sigv3 Lastly, for IMA to differentiate between the original IMA signature from an fs-verity signature a new 'xattr_type' named IMA_VERITY_DIGSIG is defined. Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx> --- Documentation/ABI/testing/ima_policy | 28 ++++++-- Documentation/security/IMA-templates.rst | 4 +- security/integrity/ima/ima_appraise.c | 79 +++++++++++++++++++++-- security/integrity/ima/ima_policy.c | 26 ++++++-- security/integrity/ima/ima_template_lib.c | 3 +- security/integrity/integrity.h | 5 +- 6 files changed, 127 insertions(+), 18 deletions(-) diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index ff3c906738cb..508053b8dd0a 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -47,7 +47,7 @@ Description: fgroup:= decimal value lsm: are LSM specific option: - appraise_type:= [imasig] [imasig|modsig] + appraise_type:= [imasig] | [imasig|modsig] | [sigv3] appraise_flag:= [check_blacklist] Currently, blacklist check is only for files signed with appended signature. @@ -153,9 +153,27 @@ Description: appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512 - Example of 'measure' rule requiring fs-verity's digests on a - particular filesystem with indication of type of digest in - the measurement list. + Example of a 'measure' rule requiring fs-verity's digests + with indication of type of digest in the measurement list. measure func=FILE_CHECK digest_type=verity \ - fsuuid=... template=ima-ngv2 + template=ima-ngv2 + + Example of 'measure' and 'appraise' rules requiring fs-verity + signatures (version 3) stored in security.ima xattr. + + The 'measure' rule specifies the 'ima-sig' template option, + which includes the file signature in the measurement list. + + measure func=BPRM_CHECK digest_type=verity \ + template=ima-sig + + The 'appraise' rule specifies the type and signature version + (sigv3) required. + + appraise func=BPRM_CHECK digest_type=verity \ + appraise_type=sigv3 + + All of these policy rules could, for example, be constrained + either based on a filesystem's UUID (fsuuid) or based on LSM + labels. diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst index 1e3fe986764e..fe9bc2595fa2 100644 --- a/Documentation/security/IMA-templates.rst +++ b/Documentation/security/IMA-templates.rst @@ -72,8 +72,8 @@ descriptors by adding their identifier to the format string - 'd-type': differentiate between fs-verity's Merkle tree based file hash from a regular IMA file hash measurement. - 'n-ng': the name of the event, without size limitations; - - 'sig': the file signature, or the EVM portable signature if the file - signature is not found; + - 'sig': the file signature, based on either the file's/fsverity's digest[1], + or the EVM portable signature if the file signature is not found; - 'modsig' the appended file signature; - 'buf': the buffer data that was used to generate the hash without size limitations; - 'evmsig': the EVM portable signature; diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index c2b429c141a7..71e27dba01ab 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -13,7 +13,9 @@ #include <linux/magic.h> #include <linux/ima.h> #include <linux/evm.h> +#include <linux/fsverity.h> #include <keys/system_keyring.h> +#include <uapi/linux/fsverity.h> #include "ima.h" @@ -183,13 +185,18 @@ enum hash_algo ima_get_hash_algo(const struct evm_ima_xattr_data *xattr_value, return ima_hash_algo; switch (xattr_value->type) { + case IMA_VERITY_DIGSIG: + sig = (typeof(sig))xattr_value; + if (sig->version != 3 || xattr_len <= sizeof(*sig) || + sig->hash_algo >= HASH_ALGO__LAST) + return ima_hash_algo; + return sig->hash_algo; case EVM_IMA_XATTR_DIGSIG: sig = (typeof(sig))xattr_value; if (sig->version != 2 || xattr_len <= sizeof(*sig) || sig->hash_algo >= HASH_ALGO__LAST) return ima_hash_algo; return sig->hash_algo; - break; case IMA_XATTR_DIGEST_NG: /* first byte contains algorithm id */ ret = xattr_value->data[0]; @@ -235,15 +242,22 @@ int ima_read_xattr(struct dentry *dentry, * IMA signature version 3 disambiguates the data that is signed by * indirectly signing the hash of the ima_file_id structure data. * + * Signing the ima_file_id struct is currently only supported for + * IMA_VERITY_DIGSIG type xattrs. + * * Return 0 on success, error code otherwise. */ static int calc_file_id_hash(enum evm_ima_xattr_type type, enum hash_algo algo, const u8 *digest, struct ima_digest_data *hash) { - struct ima_file_id file_id = {.hash_algorithm = algo}; + struct ima_file_id file_id = { + .hash_type = IMA_VERITY_DIGSIG, .hash_algorithm = algo}; uint unused = HASH_MAX_DIGESTSIZE - hash_digest_size[algo]; + if (type != IMA_VERITY_DIGSIG) + return -EINVAL; + memcpy(file_id.hash, digest, hash_digest_size[algo]); hash->algo = algo; @@ -263,6 +277,7 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint, struct evm_ima_xattr_data *xattr_value, int xattr_len, enum integrity_status *status, const char **cause) { + struct ima_max_digest_data hash; struct signature_v2_hdr *sig; int rc = -EINVAL, hash_start = 0; @@ -274,7 +289,10 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint, case IMA_XATTR_DIGEST: if (*status != INTEGRITY_PASS_IMMUTABLE) { if (iint->flags & IMA_DIGSIG_REQUIRED) { - *cause = "IMA-signature-required"; + if (iint->flags & IMA_VERITY_REQUIRED) + *cause = "verity-signature-required"; + else + *cause = "IMA-signature-required"; *status = INTEGRITY_FAIL; break; } @@ -303,6 +321,12 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint, case EVM_IMA_XATTR_DIGSIG: set_bit(IMA_DIGSIG, &iint->atomic_flags); + if (iint->flags & (IMA_DIGSIG_REQUIRED | IMA_VERITY_REQUIRED)) { + *cause = "verity-signature-required"; + *status = INTEGRITY_FAIL; + break; + } + sig = (typeof(sig))xattr_value; if (sig->version != 2) { *cause = "invalid-signature-version"; @@ -331,6 +355,44 @@ static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint, } else { *status = INTEGRITY_PASS; } + break; + case IMA_VERITY_DIGSIG: + set_bit(IMA_DIGSIG, &iint->atomic_flags); + + if (iint->flags & IMA_DIGSIG_REQUIRED) { + if (!(iint->flags & IMA_VERITY_REQUIRED)) { + *cause = "IMA-signature-required"; + *status = INTEGRITY_FAIL; + break; + } + } + + sig = (typeof(sig))xattr_value; + if (sig->version != 3) { + *cause = "invalid-signature-version"; + *status = INTEGRITY_FAIL; + break; + } + + rc = calc_file_id_hash(IMA_VERITY_DIGSIG, iint->ima_hash->algo, + iint->ima_hash->digest, &hash.hdr); + if (rc) { + *cause = "sigv3-hashing-error"; + *status = INTEGRITY_FAIL; + break; + } + + rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA, + (const char *)xattr_value, + xattr_len, hash.digest, + hash.hdr.length); + if (rc) { + *cause = "invalid-verity-signature"; + *status = INTEGRITY_FAIL; + } else { + *status = INTEGRITY_PASS; + } + break; default: *status = INTEGRITY_UNKNOWN; @@ -431,8 +493,15 @@ int ima_appraise_measurement(enum ima_hooks func, if (rc && rc != -ENODATA) goto out; - cause = iint->flags & IMA_DIGSIG_REQUIRED ? - "IMA-signature-required" : "missing-hash"; + if (iint->flags & IMA_DIGSIG_REQUIRED) { + if (iint->flags & IMA_VERITY_REQUIRED) + cause = "verity-signature-required"; + else + cause = "IMA-signature-required"; + } else { + cause = "missing-hash"; + } + status = INTEGRITY_NOLABEL; if (file->f_mode & FMODE_CREATED) iint->flags |= IMA_NEW_FILE; diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index 28aca1f9633b..d3006cc22ab1 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -1311,6 +1311,12 @@ static bool ima_validate_rule(struct ima_rule_entry *entry) !(entry->flags & IMA_MODSIG_ALLOWED)) return false; + /* Ensure APPRAISE verity file implies a v3 signature */ + if (entry->action == APPRAISE && + (entry->flags & IMA_VERITY_REQUIRED) && + !(entry->flags & IMA_DIGSIG_REQUIRED)) + return false; + return true; } @@ -1735,14 +1741,24 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) break; case Opt_appraise_type: ima_log_string(ab, "appraise_type", args[0].from); - if ((strcmp(args[0].from, "imasig")) == 0) + if ((strcmp(args[0].from, "imasig")) == 0) { entry->flags |= IMA_DIGSIG_REQUIRED; - else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) && - strcmp(args[0].from, "imasig|modsig") == 0) + } else if (strcmp(args[0].from, "sigv3") == 0) { + /* + * Only fsverity supports sigv3 for now. + * No need to define a new flag. + */ + if (entry->flags & IMA_VERITY_REQUIRED) + entry->flags |= IMA_DIGSIG_REQUIRED; + else + result = -EINVAL; + } else if (IS_ENABLED(CONFIG_IMA_APPRAISE_MODSIG) && + strcmp(args[0].from, "imasig|modsig") == 0) { entry->flags |= IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED; - else + } else { result = -EINVAL; + } break; case Opt_appraise_flag: ima_log_string(ab, "appraise_flag", args[0].from); @@ -2186,6 +2202,8 @@ int ima_policy_show(struct seq_file *m, void *v) if (entry->flags & IMA_DIGSIG_REQUIRED) { if (entry->flags & IMA_MODSIG_ALLOWED) seq_puts(m, "appraise_type=imasig|modsig "); + else if (entry->flags & IMA_VERITY_REQUIRED) + seq_puts(m, "appraise_type=sigv3 "); else seq_puts(m, "appraise_type=imasig "); } diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c index d370fca04de4..ecbe61c53d40 100644 --- a/security/integrity/ima/ima_template_lib.c +++ b/security/integrity/ima/ima_template_lib.c @@ -495,7 +495,8 @@ int ima_eventsig_init(struct ima_event_data *event_data, { struct evm_ima_xattr_data *xattr_value = event_data->xattr_value; - if ((!xattr_value) || (xattr_value->type != EVM_IMA_XATTR_DIGSIG)) + if (!xattr_value || + !(xattr_value->type & (EVM_IMA_XATTR_DIGSIG | IMA_VERITY_DIGSIG))) return ima_eventevmsig_init(event_data, field_data); return ima_write_template_field_data(xattr_value, event_data->xattr_len, diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index bd38bd451b19..b3267384c028 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -80,6 +80,7 @@ enum evm_ima_xattr_type { EVM_IMA_XATTR_DIGSIG, IMA_XATTR_DIGEST_NG, EVM_XATTR_PORTABLE_DIGSIG, + IMA_VERITY_DIGSIG, IMA_XATTR_LAST }; @@ -140,7 +141,9 @@ struct signature_v2_hdr { /* * IMA signature version 3 disambiguates the data that is signed, by - * indirectly signing the hash of the ima_file_id structure data. + * indirectly signing the hash of the ima_file_id structure data, + * containing either the fsverity_descriptor struct digest or, in the + * future, the regular IMA file hash. * * (The hash of the ima_file_id structure is only of the portion used.) */ -- 2.27.0
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