Re: [PATCH v2 7/7] ima: Support platform keyring for kernel appraisal

[Thiago Jung Bauermann]

Hello,

Nayna Jain <nayna@xxxxxxxxxxxxx> writes:

> On secure boot enabled systems, the bootloader verifies the kernel
> image and possibly the initramfs signatures based on a set of keys. A
> soft reboot(kexec) of the system, with the same kernel image and
> initramfs, requires access to the original keys to verify the
> signatures.
>
> This patch allows IMA-appraisal access to those original keys, now
> loaded on the platform keyring, needed for verifying the kernel image
> and initramfs signatures.
>
> Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxx>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
> - replace 'rc' with 'xattr_len' when calling integrity_digsig_verify()
> with INTEGRITY_KEYRING_IMA for readability
> Suggested-by: Serge Hallyn <serge@xxxxxxxxxx>
> ---
> Changelog:
>
> v2:
> - replace 'rc' with 'xattr_len' when calling integrity_digsig_verify()
> with INTEGRITY_KEYRING_IMA for readability
>
>  security/integrity/ima/ima_appraise.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index deec1804a00a..e8f520450895 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -289,12 +289,21 @@ int ima_appraise_measurement(enum ima_hooks func,
>  	case EVM_IMA_XATTR_DIGSIG:
>  		set_bit(IMA_DIGSIG, &iint->atomic_flags);
>  		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
> -					     (const char *)xattr_value, rc,
> +					     (const char *)xattr_value,
> +					     xattr_len,
>  					     iint->ima_hash->digest,
>  					     iint->ima_hash->length);
>  		if (rc == -EOPNOTSUPP) {
>  			status = INTEGRITY_UNKNOWN;
> -		} else if (rc) {
> +			break;
> +		}
> +		if (rc && func == KEXEC_KERNEL_CHECK)
> +			rc = integrity_digsig_verify(INTEGRITY_KEYRING_PLATFORM,
> +						     (const char *)xattr_value,
> +						     xattr_len,
> +						     iint->ima_hash->digest,
> +						     iint->ima_hash->length);

If CONFIG_INTEGRITY_PLATFORM_KEYRING=n the second call to
integrity_digsig_verify() above will always fail, and the audit message
of failed signature verifications for KEXEC_KERNEL will always log the
same rc value, which is whatever request_key() returns when asked to
look for an inexistent keyring.

Here is a patch which only performs the second try if the platform
keyring is enabled.