linux-hardening - Re: [PATCH] powerpc/rtas: Replace one-element arrays with flexible arrays

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Date:   Thu, 20 Apr 2023 17:46:44 +1000
From:   Andrew Donnellan <ajd@...ux.ibm.com>
To:     Nathan Lynch <nathanl@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org
Cc:     Leonardo Bras <leobras.c@...il.com>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] powerpc/rtas: Replace one-element arrays with flexible
 arrays

On Fri, 2023-01-27 at 07:10 -0600, Nathan Lynch wrote:
> > > > I see at least one place that consults the size of one of these
> > > > structs,
> > > > in get_pseries_errorlog():
> > > > 
> > > >         /* Check that we understand the format */
> > > >         if (ext_log_length < sizeof(struct
> > > > rtas_ext_event_log_v6)
> > > > ||
> > > > ...
> > > > 
> > > > Don't all such sites need to be audited/adjusted for changes
> > > > like
> > > > this?

I did actually see that site, and concluded that for the purposes of
that particular check, removing a single extra byte is irrelevant
(maybe it makes the check more strictly correct, what if the vendor_log
is actually of length 0?)

Doing a binary diff, as Kees suggests, over the object files in
arch/powerpc:

- there's no difference at all caused by changing
rtas_ext_event_log_v6.vendor_log, which kind of surprises me given the
above.

- changing rtas_error_log.buffer does seem to change some code
generation in arch/powerpc/platforms/pseries/ras.o, I can't quite see
why.

Andrew

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