Re: [RFC PATCH 1/1] KEYS, integrity: Link .platform keyring to .secondary_trusted_keys

[Mimi Zohar]

[Cc'ing the LSM and integrity mailing lists]

Repeating my comment on PATCH 0/1 here with the expanded set of
mailing lists.

The builtin and secondary keyrings have a signature change of trust
rooted in the signed kernel image.ÂÂAdding the pre-boot keys to the
secondary keyring breaks that signature chain of trust.

Please do NOT add the pre-boot "platform" keys to the secondary
keyring.

Mimi


On Tue, 2019-01-08 at 16:12 +0800, Kairui Song wrote:
> Currently kexec may need to verify the kerne image, and the kernel image
> could be signed with third part keys which are provided by paltform or
> firmware (eg. stored in MokListRT EFI variable). And the same time,
> kexec_file_load will only verify the image agains .builtin_trusted_keys
> or .secondary_trusted_keys according to configuration, but there is no
> way for kexec_file_load to verify the image against any third part keys
> mentioned above.
> 
> In ea93102f3224 ('integrity: Define a trusted platform keyring') a
> .platform keyring is introduced to store the keys provided by platform
> or firmware. And with a few following commits including 15ea0e1e3e185
> ('efi: Import certificates from UEFI Secure Boot'), now keys required to
> verify the image is being imported to .paltform keyring, and later
> IMA-appraisal could access the keyring and verify the image.
> 
> This patch links the .platform keyring to .secondary_trusted_keys so
> kexec_file_load could also leverage the .platform keyring to verify the
> kernel image.
> 
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxx>
> ---
>  certs/system_keyring.c          | 30 ++++++++++++++++++++++++++++++
>  include/keys/platform_keyring.h | 12 ++++++++++++
>  security/integrity/digsig.c     |  7 +++++++
>  3 files changed, 49 insertions(+)
>  create mode 100644 include/keys/platform_keyring.h
> 
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index 81728717523d..dcef0259e149 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -18,12 +18,14 @@
>  #include <linux/verification.h>
>  #include <keys/asymmetric-type.h>
>  #include <keys/system_keyring.h>
> +#include <keys/platform_keyring.h>
>  #include <crypto/pkcs7.h>
>  
>  static struct key *builtin_trusted_keys;
>  #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
>  static struct key *secondary_trusted_keys;
>  #endif
> +static struct key *platform_keys = NULL;
>  
>  extern __initconst const u8 system_certificate_list[];
>  extern __initconst const unsigned long system_certificate_list_size;
> @@ -67,6 +69,12 @@ int restrict_link_by_builtin_and_secondary_trusted(
>  		/* Allow the builtin keyring to be added to the secondary */
>  		return 0;
>  
> +	if (type == &key_type_keyring &&
> +	    dest_keyring == secondary_trusted_keys &&
> +	    payload == &platform_keys->payload)
> +		/* Allow the platform keyring to be added to the secondary */
> +		return 0;
> +
>  	return restrict_link_by_signature(dest_keyring, type, payload,
>  					  secondary_trusted_keys);
>  }
> @@ -188,6 +196,28 @@ static __init int load_system_certificate_list(void)
>  }
>  late_initcall(load_system_certificate_list);
>  
> +#if defined(CONFIG_INTEGRITY_PLATFORM_KEYRING) && defined(CONFIG_SECONDARY_TRUSTED_KEYRING)
> +
> +/*
> + * Link .platform keyring to .secondary_trusted_key keyring
> + */
> +static __init int load_platform_certificate_list(void)
> +{
> +	int ret = 0;
> +	platform_keys = integrity_get_platform_keyring();
> +	if (!platform_keys) {
> +		return 0;
> +	}
> +	ret = key_link(secondary_trusted_keys, platform_keys);
> +	if (ret < 0) {
> +		pr_err("Failed to link platform keyring: %d", ret);
> +	}
> +	return 0;
> +}
> +late_initcall(load_platform_certificate_list);
> +
> +#endif
> +
>  #ifdef CONFIG_SYSTEM_DATA_VERIFICATION
>  
>  /**
> diff --git a/include/keys/platform_keyring.h b/include/keys/platform_keyring.h
> new file mode 100644
> index 000000000000..4f92ed6c0b42
> --- /dev/null
> +++ b/include/keys/platform_keyring.h
> @@ -0,0 +1,12 @@
> +#ifndef _KEYS_PLATFORM_KEYRING_H
> +#define _KEYS_PLATFORM_KEYRING_H
> +
> +#include <linux/key.h>
> +
> +#ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
> +
> +extern const struct key* __init integrity_get_platform_keyring(void);
> +
> +#endif /* CONFIG_INTEGRITY_PLATFORM_KEYRING */
> +
> +#endif /* _KEYS_SYSTEM_KEYRING_H */
> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
> index f45d6edecf99..397758d4f12d 100644
> --- a/security/integrity/digsig.c
> +++ b/security/integrity/digsig.c
> @@ -176,3 +176,10 @@ int __init integrity_load_cert(const unsigned int id, const char *source,
>  	pr_info("Loading X.509 certificate: %s\n", source);
>  	return integrity_add_key(id, data, len, perm);
>  }
> +
> +#ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
> +struct key* __init integrity_get_platform_keyring(void)
> +{
> +	return keyring[INTEGRITY_KEYRING_PLATFORM];
> +}
> +#endif