Re: [PATCH v4 24/24] integrity/powerpc: Support loading keys from pseries secvar

[Russell Currey <ruscur@russell.cc>]

On Tue, 2023-01-24 at 10:14 -0500, Mimi Zohar wrote:
> On Fri, 2023-01-20 at 18:43 +1100, Andrew Donnellan wrote:
> > From: Russell Currey <ruscur@russell.cc>
> > 
> > The secvar object format is only in the device tree under powernv.
> > We now have an API call to retrieve it in a generic way, so we
> > should
> > use that instead of having to handle the DT here.
> > 
> > Add support for pseries secvar, with the "ibm,plpks-sb-v1" format.
> > The object format is expected to be the same, so there shouldn't be
> > any
> > functional differences between objects retrieved from powernv and
> > pseries.
> > 
> > Signed-off-by: Russell Currey <ruscur@russell.cc>
> > Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
> > 
> > ---
> > 
> > v3: New patch
> > 
> > v4: Pass format buffer size (stefanb, npiggin)
> > ---
> >  .../integrity/platform_certs/load_powerpc.c     | 17 ++++++++++---
> > ----
> >  1 file changed, 10 insertions(+), 7 deletions(-)
> > 
> > diff --git a/security/integrity/platform_certs/load_powerpc.c
> > b/security/integrity/platform_certs/load_powerpc.c
> > index dee51606d5f4..d4ce91bf3fec 100644
> > --- a/security/integrity/platform_certs/load_powerpc.c
> > +++ b/security/integrity/platform_certs/load_powerpc.c
> > @@ -10,7 +10,6 @@
> >  #include <linux/cred.h>
> >  #include <linux/err.h>
> >  #include <linux/slab.h>
> > -#include <linux/of.h>
> >  #include <asm/secure_boot.h>
> >  #include <asm/secvar.h>
> >  #include "keyring_handler.h"
> > @@ -59,16 +58,22 @@ static int __init load_powerpc_certs(void)
> >         void *db = NULL, *dbx = NULL;
> >         u64 dbsize = 0, dbxsize = 0;
> >         int rc = 0;
> > -       struct device_node *node;
> > +       ssize_t len;
> > +       char buf[32];
> >  
> >         if (!secvar_ops)
> >                 return -ENODEV;
> >  
> > -       /* The following only applies for the edk2-compat backend.
> > */
> > -       node = of_find_compatible_node(NULL, NULL, "ibm,edk2-
> > compat-v1");
> > -       if (!node)
> > +       len = secvar_ops->format(buf, 32);
> 
> "powerpc/secvar: Handle format string in the consumer"  defines
> opal_secvar_format() for the object format "ibm,secvar-backend". 
> Here
> shouldn't it being returning the format for "ibm,edk2-compat-v1"?
> 

They end up with the same value.  The DT structure on powernv looks
like this:

/proc/device-tree/ibm,opal/secvar:
name             "secvar"
compatible       "ibm,secvar-backend"
		 "ibm,edk2-compat-v1"
format           "ibm,edk2-compat-v1"
max-var-key-len  00000000 00000400
phandle          0000805a (32858)
max-var-size     00000000 00002000

The existing code is checking for a node compatible with "ibm,edk2-
compat-v1", which would match the node above.  opal_secvar_format()
checks for a node compatible with "ibm,secvar-backend" (again, matching
above) and then returns the contents of the "format" string, which is
"ibm,edk2-compat-v1".

Ultimately it's two different ways of doing the same thing, but this
way load_powerpc_certs() doesn't have to interact with the device tree.

- Russell


> Mimi
> 
> > +       if (len <= 0)
> >                 return -ENODEV;
> >  
> > +       // Check for known secure boot implementations from OPAL or
> > PLPKS
> > +       if (strcmp("ibm,edk2-compat-v1", buf) && strcmp("ibm,plpks-
> > sb-v1", buf)) {
> > +               pr_err("Unsupported secvar implementation \"%s\",
> > not loading certs\n", buf);
> > +               return -ENODEV;
> > +       }
> > +
> >         /*
> >          * Get db, and dbx. They might not exist, so it isn't an
> > error if we
> >          * can't get them.
> > @@ -103,8 +108,6 @@ static int __init load_powerpc_certs(void)
> >                 kfree(dbx);
> >         }
> >  
> > -       of_node_put(node);
> > -
> >         return rc;
> >  }
> >  late_initcall(load_powerpc_certs);
> 
>