Hi Jarkko,
On Sun, Aug 28, 2022 at 06:34:26AM +0300, Jarkko Sakkinen wrote:
> On Thu, Aug 25, 2022 at 10:23:12PM +0800, Lee, Chun-Yi wrote:
> > This patch adds the logic for checking the CodeSigning extended
> > key usage when verifying signature of kernel module or
> > kexec PE binary in PKCS#7.
>
> Pretty much the same feedback as for 1/4.
>
I will also change this description.
Thanks
Joey Lee
> >
> > Signed-off-by: "Lee, Chun-Yi" <jlee@xxxxxxxx>
> > ---
> > certs/blacklist.c | 5 ++--
> > certs/system_keyring.c | 4 +--
> > crypto/asymmetric_keys/Kconfig | 9 ++++++
> > crypto/asymmetric_keys/pkcs7_trust.c | 43 ++++++++++++++++++++++++++--
> > crypto/asymmetric_keys/selftest.c | 2 +-
> > include/crypto/pkcs7.h | 4 ++-
> > include/keys/system_keyring.h | 7 +++--
> > 7 files changed, 63 insertions(+), 11 deletions(-)
> >
> > diff --git a/certs/blacklist.c b/certs/blacklist.c
> > index 41f10601cc72..fa41454055be 100644
> > --- a/certs/blacklist.c
> > +++ b/certs/blacklist.c
> > @@ -282,11 +282,12 @@ int add_key_to_revocation_list(const char *data, size_t size)
> > * 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 is_key_on_revocation_list(struct pkcs7_message *pkcs7,
> > + enum key_being_used_for usage)
> > {
> > int ret;
> >
> > - ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
> > + ret = pkcs7_validate_trust(pkcs7, blacklist_keyring, usage, false);
> >
> > if (ret == 0)
> > return -EKEYREJECTED;
> > diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> > index 5042cc54fa5e..66737bfb26de 100644
> > --- a/certs/system_keyring.c
> > +++ b/certs/system_keyring.c
> > @@ -263,13 +263,13 @@ int verify_pkcs7_message_sig(const void *data, size_t len,
> > goto error;
> > }
> >
> > - ret = is_key_on_revocation_list(pkcs7);
> > + ret = is_key_on_revocation_list(pkcs7, usage);
> > if (ret != -ENOKEY) {
> > pr_devel("PKCS#7 platform key is on revocation list\n");
> > goto error;
> > }
> > }
> > - ret = pkcs7_validate_trust(pkcs7, trusted_keys);
> > + ret = pkcs7_validate_trust(pkcs7, trusted_keys, usage, true);
> > if (ret < 0) {
> > if (ret == -ENOKEY)
> > pr_devel("PKCS#7 signature not signed with a trusted key\n");
> > diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
> > index 3df3fe4ed95f..189536bd0f9a 100644
> > --- a/crypto/asymmetric_keys/Kconfig
> > +++ b/crypto/asymmetric_keys/Kconfig
> > @@ -85,4 +85,13 @@ config FIPS_SIGNATURE_SELFTEST
> > depends on ASYMMETRIC_KEY_TYPE
> > depends on PKCS7_MESSAGE_PARSER
> >
> > +config CHECK_CODESIGN_EKU
> > + bool "Check codeSigning extended key usage"
> > + depends on PKCS7_MESSAGE_PARSER=y
> > + depends on SYSTEM_DATA_VERIFICATION
> > + help
> > + This option provides support for checking the codeSigning extended
> > + key usage when verifying the signature in PKCS#7. It affects kernel
> > + module verification and kexec PE binary verification.
> > +
> > endif # ASYMMETRIC_KEY_TYPE
> > diff --git a/crypto/asymmetric_keys/pkcs7_trust.c b/crypto/asymmetric_keys/pkcs7_trust.c
> > index 9a87c34ed173..087d3761d9a8 100644
> > --- a/crypto/asymmetric_keys/pkcs7_trust.c
> > +++ b/crypto/asymmetric_keys/pkcs7_trust.c
> > @@ -16,12 +16,40 @@
> > #include <crypto/public_key.h>
> > #include "pkcs7_parser.h"
> >
> > +#ifdef CONFIG_CHECK_CODESIGN_EKU
> > +static bool check_eku_by_usage(struct key *key, enum key_being_used_for usage)
> > +{
> > + struct public_key *public_key = key->payload.data[asym_crypto];
> > + bool ret = true;
> > +
> > + switch (usage) {
> > + case VERIFYING_MODULE_SIGNATURE:
> > + case VERIFYING_KEXEC_PE_SIGNATURE:
> > + ret = !!(public_key->ext_key_usage & EKU_codeSigning);
> > + if (!ret)
> > + pr_warn("The signer '%s' key is not CodeSigning\n",
> > + key->description);
> > + break;
> > + default:
> > + break;
> > + }
> > + return ret;
> > +}
> > +#else
> > +static bool check_eku_by_usage(struct key *key, enum key_being_used_for usage)
> > +{
> > + return true;
> > +}
> > +#endif
> > +
> > /*
> > * Check the trust on one PKCS#7 SignedInfo block.
> > */
> > static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > struct pkcs7_signed_info *sinfo,
> > - struct key *trust_keyring)
> > + struct key *trust_keyring,
> > + enum key_being_used_for usage,
> > + bool check_eku)
> > {
> > struct public_key_signature *sig = sinfo->sig;
> > struct x509_certificate *x509, *last = NULL, *p;
> > @@ -112,6 +140,10 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > return -ENOKEY;
> >
> > matched:
> > + if (check_eku && !check_eku_by_usage(key, usage)) {
> > + key_put(key);
> > + return -ENOKEY;
> > + }
>
> Why you don't just open code this to those rare call
> sites where it is needed?
>
> I counted that there is exactly one call site.
>
> > ret = verify_signature(key, sig);
> > key_put(key);
> > if (ret < 0) {
> > @@ -135,6 +167,8 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > * pkcs7_validate_trust - Validate PKCS#7 trust chain
> > * @pkcs7: The PKCS#7 certificate to validate
> > * @trust_keyring: Signing certificates to use as starting points
> > + * @usage: The use to which the key is being put.
> > + * @check_eku: Check EKU (Extended Key Usage)
> > *
> > * Validate that the certificate chain inside the PKCS#7 message intersects
> > * keys we already know and trust.
> > @@ -156,7 +190,9 @@ static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
> > * May also return -ENOMEM.
> > */
> > int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
> > - struct key *trust_keyring)
> > + struct key *trust_keyring,
> > + enum key_being_used_for usage,
> > + bool check_eku)
> > {
> > struct pkcs7_signed_info *sinfo;
> > struct x509_certificate *p;
> > @@ -167,7 +203,8 @@ int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
> > p->seen = false;
> >
> > for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
> > - ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
> > + ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring,
> > + usage, check_eku);
> > switch (ret) {
> > case -ENOKEY:
> > continue;
> > diff --git a/crypto/asymmetric_keys/selftest.c b/crypto/asymmetric_keys/selftest.c
> > index fa0bf7f24284..756e9f224d8a 100644
> > --- a/crypto/asymmetric_keys/selftest.c
> > +++ b/crypto/asymmetric_keys/selftest.c
> > @@ -212,7 +212,7 @@ int __init fips_signature_selftest(void)
> > if (ret < 0)
> > panic("Certs selftest %d: pkcs7_verify() = %d\n", i, ret);
> >
> > - ret = pkcs7_validate_trust(pkcs7, keyring);
> > + ret = pkcs7_validate_trust(pkcs7, keyring, VERIFYING_MODULE_SIGNATURE, false);
> > if (ret < 0)
> > panic("Certs selftest %d: pkcs7_validate_trust() = %d\n", i, ret);
> >
> > diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
> > index 38ec7f5f9041..5d87b8a02f79 100644
> > --- a/include/crypto/pkcs7.h
> > +++ b/include/crypto/pkcs7.h
> > @@ -30,7 +30,9 @@ extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
> > * pkcs7_trust.c
> > */
> > extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
> > - struct key *trust_keyring);
> > + struct key *trust_keyring,
> > + enum key_being_used_for usage,
> > + bool check_eku);
> >
> > /*
> > * pkcs7_verify.c
> > diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> > index 91e080efb918..bb33b527240e 100644
> > --- a/include/keys/system_keyring.h
> > +++ b/include/keys/system_keyring.h
> > @@ -9,6 +9,7 @@
> > #define _KEYS_SYSTEM_KEYRING_H
> >
> > #include <linux/key.h>
> > +#include <keys/asymmetric-type.h>
> >
> > enum blacklist_hash_type {
> > /* TBSCertificate hash */
> > @@ -81,13 +82,15 @@ static inline int is_binary_blacklisted(const u8 *hash, size_t hash_len)
> >
> > #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);
> > +extern int is_key_on_revocation_list(struct pkcs7_message *pkcs7,
> > + enum key_being_used_for usage);
> > #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)
> > +static inline int is_key_on_revocation_list(struct pkcs7_message *pkcs7,
> > + enum key_being_used_for usage)
> > {
> > return -ENOKEY;
> > }
> > --
> > 2.26.2
> >
>
> BR, Jarkko
