linux-kernel - Re: [PATCH 1/3] powerpc/pseries: Correct secvar format representation for static key management

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Message-ID: <e80c83a1-77db-452e-8a5d-d435e61bd544@linux.ibm.com>
Date: Wed, 7 May 2025 21:18:44 +0530
From: Srish Srinivasan <ssrish@...ux.ibm.com>
To: Andrew Donnellan <ajd@...ux.ibm.com>, linux-integrity@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Cc: maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
        christophe.leroy@...roup.eu, naveen@...nel.org, zohar@...ux.ibm.com,
        nayna@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] powerpc/pseries: Correct secvar format representation
 for static key management


On 5/7/25 11:47 AM, Andrew Donnellan wrote:
> On Wed, 2025-05-07 at 00:29 +0530, Srish Srinivasan wrote:
>>>> +	rc = plpks_read_fw_var(&var);
>>>> +	if (rc) {
>>>> +		pr_info("Error %ld reading SB_VERSION from
>>>> firmware\n", rc);
>>> We need to check for -ENOENT, otherwise this message is going to be
>>> printed every time you boot a machine in static mode.
>> Yes, I agree with your concern. I just want to add that, as per my
>> understanding, we need to check for both -ENOENT and -EPERM,
>> as explained below:
>>
>> As per H_PKS_READ_OBJECT semantics described in the PAPR v10.60
>> (https://files.openpower.foundation/s/XFgfMaqLMD5Bcm8),
>>
>> * If the object is not world readable, verify that the consumer
>> password
>> matches the stored value in the hypervisor. Else return H_AUTHORITY.
>> * Verify if the object exists, else return H_NOT_FOUND.
>> * Verify if the policy for the object is met, else return
>> H_AUTHORITY.
>>
>> So, the hypervisor returns H_NOT_FOUND only for the authenticated
>> consumer. For unauthenticated consumers, which is the case here,
>> it would return H_AUTHORITY.
> We expect SB_VERSION to always be world-readable, I think? In which
> case it shouldn't return H_AUTHORITY / -EPERM, ever, and if it does
> that's an error which should be handled as an error. Or am I
> misinterpreting the spec here?

Yes, SB_VERSION is world-readable and should not return H_AUTHORITY in 
the case of dynamic key management mode. However, in
the case of static key management mode, when SB_VERSION does not exist, 
the hypervisor tries to authenticate the consumer. If the
authentication is successful, H_NOT_FOUND is returned, else H_AUTHORITY 
is returned. The intention behind authenticating the
consumer when the object is not found is to ensure that a 
non-authenticated consumer is unable to conclude on the absence of
the object. Here, when the kernel tries to read the non-existent 
SB_VERSION, it fails the authentication check and therefore,
gets the H_AUTHORITY error code.

>
>