linux-kernel - Re: [PATCH v2] KEYS: Make use of platform keyring for module signature verify

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Date:   Thu, 25 Apr 2019 07:55:50 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Robert Holmes <robeholmes@...il.com>, jeyu@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] KEYS: Make use of platform keyring for module
 signature verify

On Wed, 2019-04-24 at 14:33 +0000, Robert Holmes wrote:
> This patch completes commit 278311e417be ("kexec, KEYS: Make use of
> platform keyring for signature verify") which, while adding the
> platform keyring for bzImage verification, neglected to also add
> this keyring for module verification.
> 
> As such, kernel modules signed with keys from the MokList variable
> were not successfully verified.

Using the platform keyring keys for verifying kernel modules was not
neglected, but rather intentional.  This patch description should
clearly explain the reason for needing to verify kernel module
signatures based on the pre-boot keys.  (Hint: verifying kernel
modules based on the pre-boot keys was previously rejected.)

Mimi

> 
> Signed-off-by: Robert Holmes <robeholmes@...il.com>
> Cc: linux-integrity@...r.kernel.org
> Cc: keyrings@...r.kernel.org
> Cc: stable@...r.kernel.org
> ---
>  kernel/module_signing.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/module_signing.c b/kernel/module_signing.c
> index 6b9a926fd86b..cf94220e9154 100644
> --- a/kernel/module_signing.c
> +++ b/kernel/module_signing.c
> @@ -49,6 +49,7 @@ int mod_verify_sig(const void *mod, struct load_info *info)
>  {
>  	struct module_signature ms;
>  	size_t sig_len, modlen = info->len;
> +	int ret;
> 
>  	pr_devel("==>%s(,%zu)\n", __func__, modlen);
> 
> @@ -82,8 +83,15 @@ int mod_verify_sig(const void *mod, struct load_info *info)
>  		return -EBADMSG;
>  	}
> 
> -	return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
> -				      VERIFY_USE_SECONDARY_KEYRING,
> -				      VERIFYING_MODULE_SIGNATURE,
> -				      NULL, NULL);
> +	ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
> +				     VERIFY_USE_SECONDARY_KEYRING,
> +				     VERIFYING_MODULE_SIGNATURE,
> +				     NULL, NULL);
> +	if (ret == -ENOKEY && IS_ENABLED(CONFIG_INTEGRITY_PLATFORM_KEYRING)) {
> +		ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
> +					     VERIFY_USE_PLATFORM_KEYRING,
> +					     VERIFYING_MODULE_SIGNATURE,
> +					     NULL, NULL);
> +	}
> +	return ret;
>  }