Re: [PATCH 1/3] keys: add KEY_SPEC_DM_VERITY_KEYRING

[Andrew Halaney <andrew@amutable.com>]

On Fri, Sep 25, 2026 at 11:39:28AM +0300, Jarkko Sakkinen wrote:
> On Fri, Sep 18, 2026 at 02:59:49PM -0500, Andrew Halaney wrote:
> > On Fri, Sep 18, 2026 at 09:05:26AM +0100, David Howells wrote:
> > > Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > > 
> > > > This is great for discussion but what we want for the commit message
> > > > is just motivation and resolution.
> > > 
> > > Actually, I think it's useful that Andrew wrote up the issues in the commit
> > > message - and I think it shows part of the motivation.  The 'writing a fake
> > > /proc/keys line in the description' is something I hadn't considered.
> > 
> > I'll defer to what you all want in the message here, I found it valuable
> > but I trend on the side of overly verbose admittedly!
> > 
> > > 
> > > > I don't think we need all this just to say that /proc/keys in a racy
> > > > query mechanism for production, which is an issue for dm-verity, given
> > > > that nothing else is available.
> > > 
> > > I think at some point, we will need a system call to search all for all
> > > accessible keys matching certain criteria by actually walking the key
> > > database.  The problem there is that there may be multiple hits, so we may
> > > need something like:
> > > 
> > > 	int count = find_key(key_serial_t start_id,
> > > 			     const char *type, const char *desc_prefix,
> > > 			     key_serial_t *results, size_t results_size,
> > > 			     unsigned int flags);
> > > 
> > > Allowing you to do:
> > > 
> > > 	key_serial_t dm_key;
> > > 	int n = find_key(0, "keyring", ".dm_verity", &dm_key, 1,
> > > 			 FIND_KEY_EXACT_DESC);
> > > 
> > > This wouldn't be as fast as a direct lookup since it would have to walk the
> > > key tree, doing name comparisons and perm checks on each key of the type.
> > > 
> > > > And secondly special keys are meant for implicit keyrings so isn't
> > > > that all there's to it?
> > > 
> > > I have no particular objection to setting aside a block of negative key IDs
> > > for special keyrings that need to be accessed a lot - though I would make
> > > common reg/unreg functions that take the ID to be registered and, say, set the
> > > block at -257..-512.  Moving the BFP keyring to -257 and DM to -258.
> > 
> > To be clear are you suggesting I do that for v2 here? Happy to make the
> > change and add some reuse to the registration functions, etc. I'm
> > guessing its fine to change the bpf id since its still only in -next?
> > 
> > The only awkward bit with making that more generic is that dm-verity
> > isn't __ro_after_init since its coming from a module possibly, and
> > because of the module usage I also protected it with a spinlock in case
> > someone's accessing it while you unload the module. Could just use one
> > spinlock for the whole generic array, and drop the __ro_after_init I
> > suppose.
> > 
> > Let me know if I'm not following properly!
> 
> I just read David's response and I think he made fair arguments,
> and patches look fine to me.
> 
> David, did you have anything? I could pick these.
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> 

Gentle ping :)

Are we happy with these to get picked up?

Thanks,
Andrew