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

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Message-ID: <0c0daff7b3674d2520e0fe24af4afcac49b53049.camel@linux.ibm.com>
Date: Mon, 12 May 2025 19:51:00 +1000
From: Andrew Donnellan <ajd@...ux.ibm.com>
To: Srish Srinivasan <ssrish@...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 Wed, 2025-05-07 at 21:18 +0530, Srish Srinivasan wrote:
> > 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.

Ah, I see my confusion: if the object *doesn't exist*, then it
obviously can't be a world-readable object, thus triggering the
password verification. In which case, we do need to catch -EPERM.

Thanks for correcting me!

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@...ux.ibm.com   IBM Australia Limited