linux-kernel - Re: [RFC PATCH v2 02/13] ima: always create runtime_measurements sysfs file for ima

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Message-ID: <35d199c2a09e9215aad715c97a6702dd04be4a98.camel@linux.ibm.com>
Date: Mon, 24 Mar 2025 10:31:47 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Nicolai Stange <nstange@...e.de>,
        Roberto Sassu
 <roberto.sassu@...wei.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc: Eric Snowberg <eric.snowberg@...cle.com>,
        Jarkko Sakkinen
 <jarkko@...nel.org>,
        James Bottomley
 <James.Bottomley@...senPartnership.com>,
        linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 02/13] ima: always create runtime_measurements
 sysfs file for ima_hash

On Sun, 2025-03-23 at 15:09 +0100, Nicolai Stange wrote:
> runtime_measurements_<hash-algo> sysfs files are getting created for
> each PCR bank + for SHA-1.
> 
> Now that runtime_measurements_<hash-algo> sysfs file creation is being
> skipped for unsupported hash algorithms, it will become possible that no
> such file would be provided at all once SHA-1 is made optional in a
> later patch.
> 
> Always create the file for the 'ima_hash' algorithm, even if it's not
> associated with any of the PCR banks. As IMA initialization will
> continue to fail if the ima_hash algorithm is not available to the
> kernel, this guarantees that at least one such file will always be
> there.
> 
> Signed-off-by: Nicolai Stange <nstange@...e.de>
> ---
>  security/integrity/ima/ima_fs.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index a8df2fe5f4cb..f030ff7f56da 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -436,10 +436,8 @@ static int __init create_securityfs_measurement_lists(void)
>  	u16 algo;
>  	int i;
>  
> -	securityfs_measurement_list_count = NR_BANKS(ima_tpm_chip);
> -
> -	if (ima_sha1_idx >= NR_BANKS(ima_tpm_chip))
> -		securityfs_measurement_list_count++;
> +	securityfs_measurement_list_count =
> +		NR_BANKS(ima_tpm_chip) + ima_extra_slots;
>  
>  	ascii_securityfs_measurement_lists =
>  	    kcalloc(securityfs_measurement_list_count, sizeof(struct dentry *),

"ima_hash" is the default file hash algorithm.  Re-using it as the default
complete measurement list assumes that the subsequent kexec'ed kernels configure
and define it as the default file hash algorithm as well, which might not be the
case.  Drop this patch.

Defer allocating the "extra" non-sha1 bank.  A subsequent patch will select
SHA256.  Based on the chosen algorithm, define the "extra" non-sha1 bank.

thanks,

Mimi