linux-hardening - Re: [PATCH v4 1/1] exec: seal system mappings

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Message-ID: <37817840-66d5-4208-b5d4-5f941ea6b95f@lucifer.local>
Date: Mon, 2 Dec 2024 17:57:32 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jeff Xu <jeffxu@...omium.org>
Cc: Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
        keescook@...omium.org, jannh@...gle.com, torvalds@...ux-foundation.org,
        adhemerval.zanella@...aro.org, oleg@...hat.com,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
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Subject: Re: [PATCH v4 1/1] exec: seal system mappings

On Mon, Dec 02, 2024 at 09:22:33AM -0800, Jeff Xu wrote:
> On Mon, Nov 25, 2024 at 12:40 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Mon, Nov 25, 2024 at 08:20:21PM +0000, jeffxu@...omium.org wrote:
> > > +/*
> > > + * Kernel cmdline override for CONFIG_SEAL_SYSTEM_MAPPINGS
> > > + */
> > > +enum seal_system_mappings_type {
> > > +     SEAL_SYSTEM_MAPPINGS_DISABLED,
> > > +     SEAL_SYSTEM_MAPPINGS_ENABLED
> > > +};
> > > +
> > > +static enum seal_system_mappings_type seal_system_mappings_v __ro_after_init =
> > > +     IS_ENABLED(CONFIG_SEAL_SYSTEM_MAPPINGS) ? SEAL_SYSTEM_MAPPINGS_ENABLED :
> > > +     SEAL_SYSTEM_MAPPINGS_DISABLED;
> > > +
> > > +static const struct constant_table value_table_sys_mapping[] __initconst = {
> > > +     { "no", SEAL_SYSTEM_MAPPINGS_DISABLED},
> > > +     { "yes", SEAL_SYSTEM_MAPPINGS_ENABLED},
> > > +     { }
> > > +};
> > > +
> > > +static int __init early_seal_system_mappings_override(char *buf)
> > > +{
> > > +     if (!buf)
> > > +             return -EINVAL;
> > > +
> > > +     seal_system_mappings_v = lookup_constant(value_table_sys_mapping,
> > > +                     buf, seal_system_mappings_v);
> > > +     return 0;
> > > +}
> > > +
> > > +early_param("exec.seal_system_mappings", early_seal_system_mappings_override);
> >
> > Are you paid by the line?
> > This all seems ridiculously overcomplicated.
> > Look at (first example I found) kgdbwait:
> >
> The example you provided doesn't seem to support the kernel cmd-line ?
>
> > static int __init opt_kgdb_wait(char *str)
> > {
> >         kgdb_break_asap = 1;
> >
> >         kdb_init(KDB_INIT_EARLY);
> >         if (kgdb_io_module_registered &&
> >             IS_ENABLED(CONFIG_ARCH_HAS_EARLY_DEBUG))
> >                 kgdb_initial_breakpoint();
> >
> >         return 0;
> > }
> > early_param("kgdbwait", opt_kgdb_wait);
> >
> There is an existing pattern of supporting kernel cmd line + KCONFIG
> which I followed [1],
> IMO, this fits this user-case really well, if you have a better
> example, I'm happy to look.
>
> [1] https://lore.kernel.org/lkml/20240802080225.89408-1-adrian.ratiu@collabora.com/
>
> > I don't understand why you've created a new 'exec' namespace, and why
> > this feature fits in 'exec'.  That seems like an implementation detail.
> > I'd lose the "exec." prefix.
>
> I would prefer some prefix to group these types of features.
> vdso/vvar are sealed during the execve() call, so I choose "exec".
> The next work I'm planning is sealing the NX stack, it would start
> with the same prefix.
>
>  If exec is not an intuitive prefix, I'm also happy with "process." prefix.

If we HAVE to have a prefix, I'd prefer "mseal.". 'Seal' is horribly
overloaded and I'd prefer to group these operations together.

>
> Thanks for reviewing
>
> -Jeff