Re: [PATCH 3/3] integrity: Load keys from TPM NV onto IMA keyring

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/25/21 3:32 PM, Patrick Uiterwijk wrote:
> Allows users to enroll their own public key stored in a specific TPM2
> NV Index, requiring the absence of the Platform Create and Platform
> Write attributes on the NV Index, to be loaded on the IMA keyring.
>
> Provides a method for users to load keys without the need to recompile
> the kernel or change the kernel binary, which would require a resign of
> the kernel image.
>
> Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>
> ---
>   security/integrity/ima/Kconfig    | 22 +++++++++++++
>   security/integrity/ima/ima_init.c | 53 +++++++++++++++++++++++++++++++
>   2 files changed, 75 insertions(+)
>
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 12e9250c1bec..28424b930c81 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -291,6 +291,28 @@ config IMA_BLACKLIST_KEYRING
>   	   the search is successful the requested operation is rejected and
>   	   an error is returned to the caller.
>   
> +config IMA_LOAD_CERT_NVINDEX
> +	bool "Load certificate from TPM nvindex into '.ima' trusted keyring"
> +	depends on IMA_TRUSTED_KEYRING && TCG_TPM
> +	default n
> +	help
> +	   File signature verification is based on the public keys
> +	   loaded on the .ima trusted keyring. These public keys are
> +	   X509 certificates signed by a trusted key on the
> +	   .system keyring.  This option enables X509 certificate
> +	   loading by the kernel onto the '.ima' trusted keyring
> +	   from a TPM nvindex, bypassing the builtin keyring check.
> +
> +config IMA_LOAD_CERT_NVINDEX_INDEX
> +	hex "The TPM NV Index to load into the '.ima' trusted keyring"
> +	depends on IMA_LOAD_CERT_NVINDEX
> +	default 0x184b520
> +	help
> +	   Defines the index of the NV Index that gets loaded into the
> +	   '.ima' keyring.
> +	   The default is the "0x18" prefix for a non-TCG specified NV Index,
> +	   suffixed with ASCII for "KR" (keyring) and then 0
> +
>   config IMA_LOAD_X509
>   	bool "Load X509 certificate onto the '.ima' trusted keyring"
>   	depends on IMA_TRUSTED_KEYRING
> diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
> index 6e8742916d1d..ea0949e8df12 100644
> --- a/security/integrity/ima/ima_init.c
> +++ b/security/integrity/ima/ima_init.c
> @@ -112,6 +112,55 @@ void __init ima_load_x509(void)
>   }
>   #endif
>   
> +#ifndef CONFIG_IMA_LOAD_CERT_NVINDEX
> +int __init ima_load_key_nvindex(void)
> +{
> +	return 0;
> +}
> +#else
> +int __init ima_load_key_nvindex(void)
> +{
> +	void *cert_buffer;
> +	int rc;
> +	key_perm_t perm;
> +	u32 nvindex_attributes = 0;
> +
> +	rc = tpm_nv_read(tpm_default_chip(),


You should do chip = tpm_default_chip() so that later on you can do 
put_device(&chip->dev).


> +				CONFIG_IMA_LOAD_CERT_NVINDEX_INDEX,
> +				&nvindex_attributes, &cert_buffer);
> +	if (rc < 0) {
> +		if (rc == -ENODEV)  /* No TPM2 */
> +			rc = 0;
> +		if (rc == -ENOENT)  /* No certificate in NV Index */
> +			rc = 0;
> +		goto out;
> +	}
> +
> +	pr_info("Loading IMA key from TPM NV Index 0x%x", CONFIG_IMA_LOAD_CERT_NVINDEX_INDEX);
> +
> +	if (nvindex_attributes & TPM2_ATTR_NV_PLATFORMCREATE) {
> +		pr_err("NV Index has the Platform Create attribute");
> +		rc = -EACCES;
> +		goto out_free;
> +	}
> +	if (nvindex_attributes & TPM2_ATTR_NV_PPWRITE) {
> +		pr_err("NV Index has the Platform Write attribute");
> +		rc = -EACCES;
> +		goto out_free;
> +	}
> +
> +	perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW | KEY_USR_READ;
> +	rc = integrity_load_cert(INTEGRITY_KEYRING_IMA, "TPM NV Index",
> +				 cert_buffer, rc, perm,
> +				 KEY_ALLOC_BYPASS_RESTRICTION);
> +
> +out_free:
> +	kvfree(cert_buffer);


kfree?


> +out:
> +	return rc;
> +}
> +#endif
> +
>   int __init ima_init(void)
>   {
>   	int rc;
> @@ -124,6 +173,10 @@ int __init ima_init(void)
>   	if (rc)
>   		return rc;
>   
> +	rc = ima_load_key_nvindex();
> +	if (rc)
> +		pr_info("Failed to load IMA key from TPM NV Index (%d)", rc);
> +
>   	rc = ima_init_crypto();
>   	if (rc)
>   		return rc;