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

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Message-ID: <CABi2SkV9=LPYfzO9eWZmTxrie_pqLEDmv0pcYHwtRcL4Teuzfw@mail.gmail.com>
Date: Mon, 2 Dec 2024 12:05:02 -0800
From: Jeff Xu <jeffxu@...omium.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org, keescook@...omium.org, 
	jannh@...gle.com, torvalds@...ux-foundation.org, 
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	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v4 1/1] exec: seal system mappings

On Mon, Dec 2, 2024 at 9:57 AM Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> 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.
>
mseal.seal_system_mappings seems to contain duplicate info.

If the norm is against prefix in kernel cmd line, I will drop the prefix and use
mseal_system_mappings

> >
> > Thanks for reviewing
> >
> > -Jeff