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

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Date:   Thu, 6 Dec 2018 17:09:16 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Nayna Jain <nayna@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, zohar@...ux.ibm.com,
        dhowells@...hat.com, jforbes@...hat.com,
        seth.forshee@...onical.com, kexec@...ts.infradead.org,
        keyrings@...r.kernel.org, vgoyal@...hat.com, ebiederm@...ssion.com,
        mpe@...erman.id.au
Subject: Re: [PATCH 7/7] ima: Support platform keyring for kernel appraisal

On Sun, Nov 25, 2018 at 08:45:00PM +0530, Nayna Jain wrote:
> 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@...ux.ibm.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>

The overall set seems sensible to me, and I see no errors here,

Acked-by: Serge Hallyn <serge@...lyn.com>

I do think that replacing the 'rc' with xattr_len in the previous line might
help future readers save a few cycles.

> ---
>  security/integrity/ima/ima_appraise.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index deec1804a00a..9c13585e7d3e 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -294,7 +294,16 @@ int ima_appraise_measurement(enum ima_hooks func,
>  					     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 (rc) {
>  			cause = "invalid-signature";
>  			status = INTEGRITY_FAIL;
>  		} else {
> -- 
> 2.13.6
>