linux-kernel - Re: [PATCH 4/5] selinux: declare data arrays const

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Message-ID: <CAHC9VhSKZes9g_GHMKJdhd_BEt7GT4FKOLeMJ=o=FU8TtOZ-gg@mail.gmail.com>
Date:   Tue, 22 Feb 2022 18:16:33 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Christian Göttsche <cgzones@...glemail.com>,
        selinux@...r.kernel.org,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Jeremy Kerr <jk@...econstruct.com.au>,
        "David S. Miller" <davem@...emloft.net>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Yang Li <yang.lee@...ux.alibaba.com>,
        Austin Kim <austin.kim@....com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH 4/5] selinux: declare data arrays const

On Fri, Feb 18, 2022 at 12:24 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> On Fri, Feb 18, 2022 at 8:13 AM Paul Moore <paul@...l-moore.com> wrote:
> > On Thu, Feb 17, 2022 at 9:21 AM Christian Göttsche
> > <cgzones@...glemail.com> wrote:
> > >
> > > diff --git a/security/selinux/include/initial_sid_to_string.h b/security/selinux/include/initial_sid_to_string.h
> > > index 5d332aeb8b6c..915283cd89bd 100644
> > > --- a/security/selinux/include/initial_sid_to_string.h
> > > +++ b/security/selinux/include/initial_sid_to_string.h
> > > @@ -1,5 +1,12 @@
> > >  /* SPDX-License-Identifier: GPL-2.0 */
> > > -static const char *initial_sid_to_string[] =
> > > +
> > > +#ifdef __SELINUX_GENHEADERS__
> > > +# define const_qual
> > > +#else
> > > +# define const_qual const
> > > +#endif
> > > +
> > > +static const char *const_qual initial_sid_to_string[] =
> > >  {
> > >         NULL,
> > >         "kernel",
> >
> > Thanks for this Christian.  I generally like when we can const'ify
> > things like this, but I'm not excited about the const_qual hack on
> > core SELinux kernel code to satisfy genheaders.c.  I understand why it
> > is needed, but I would rather clutter the genheaders.c code than the
> > core SELinux kernel code.  If we can't cast away the const'ification
> > in genheaders.c could we simply allocate duplicate arrays in
> > genheaders.c and store the transformed strings into the new arrays?
>
> Note: casting off const is UB. I've had to fix multiple bugs where
> clang will drop writes to variables declared const but had const'ness
> casted away.

Then let's just memcpy the array in genheaders.c.  I'm okay with
genheaders being a little ugly if it helps keep the core code cleaner.

-- 
paul-moore.com