linux-kernel - Re: [RFC PATCH 2/2] kexec, KEYS: Make use of platform keyring for signature verify

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Date:   Tue, 15 Jan 2019 10:42:43 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Kairui Song <kasong@...hat.com>, linux-kernel@...r.kernel.org,
        dhowells@...hat.com, dwmw2@...radead.org,
        jwboyer@...oraproject.org, keyrings@...r.kernel.org,
        jmorris@...ei.org, serge@...lyn.com, bauerman@...ux.ibm.com,
        ebiggers@...gle.com, nayna@...ux.ibm.com,
        linux-integrity@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 2/2] kexec, KEYS: Make use of platform keyring for
 signature verify

On 01/14/19 at 11:10am, Mimi Zohar wrote:
> On Sun, 2019-01-13 at 09:39 +0800, Dave Young wrote:
> > Hi,
> > 
> > On 01/11/19 at 11:13am, Mimi Zohar wrote:
> > > On Fri, 2019-01-11 at 21:43 +0800, Dave Young wrote:
> > > [snip]
> > > 
> > > > Personally I would like to see platform key separated from integrity.
> > > > But for the kexec_file part I think it is good at least it works with
> > > > this fix.
> > > > 
> > > > Acked-by: Dave Young <dyoung@...hat.com>
> > > 
> > > The original "platform" keyring patches that Nayna posted multiple
> > > times were in the certs directory, but nobody commented/responded.  So
> > > she reworked the patches, moving them to the integrity directory and
> > > posted them (cc'ing the kexec mailing list).  It's a bit late to be
> > > asking to move it, isn't it?
> > 
> > Hmm, apologize for being late,  I did not get chance to have a look the
> > old series.  Since we have the needs now, it should be still fine
> > 
> > Maybe Kairui can check Nayna's old series, see if he can do something
> > again?
> 
> Whether the platform keyring is defined in certs/ or in integrity/ the
> keyring id needs to be accessible to the other, without making the
> keyring id global.  Moving where the platform keyring is defined is
> not the problem.

Agreed, but just feel kexec depends on IMA sounds not good.

> 
> Commit a210fd32a46b ("kexec: add call to LSM hook in original
> kexec_load syscall") introduced a new LSM hook.  Assuming
> CONFIG_KEXEC_VERIFY_SIG is enabled, with commit b5ca117365d9 ("ima:
> prevent kexec_load syscall based on runtime secureboot flag") we can
> now block the kexec_load syscall.  Without being able to block the
> kexec_load syscall, verifying the kexec image signature via the
> kexec_file_load syscall is kind of pointless.
> 
> Unless you're planning on writing an LSM to prevent the kexec_load
> syscall, I assume you'll want to enable integrity anyway.

User can disable kexec_load in kernel config, and only allow
kexec_file_load.  But yes, this can be improved separately in case no
IMA enabled.

For the time being we can leave with it and fix like this series do.

> 
> Mimi
> 

Thanks
Dave