linux-kernel - Re: [RFC PATCH 3/7] static_call: use helper to access non-exported key

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Date:   Tue, 9 Nov 2021 20:42:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH 3/7] static_call: use helper to access non-exported
 key

On Tue, Nov 09, 2021 at 07:54:23PM +0100, Ard Biesheuvel wrote:
> On Tue, 9 Nov 2021 at 19:53, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Tue, Nov 09, 2021 at 05:45:45PM +0100, Ard Biesheuvel wrote:
> > > @@ -196,13 +190,21 @@ extern long __static_call_return0(void);
> > >       EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name));                       \
> > >       EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
> > >
> > > +#define EXPORT_STATIC_CALL_GETKEY_HELPER(name)                               \
> > > +     struct static_call_key *STATIC_CALL_GETKEY(name)(void) {        \
> > > +             BUG_ON(!core_kernel_text(                               \
> > > +                     (unsigned long)__builtin_return_address(0)));   \
> > > +             return &STATIC_CALL_KEY(name);                          \
> > > +     }                                                               \
> > > +     EXPORT_SYMBOL_GPL(STATIC_CALL_GETKEY(name))
> >
> > So if I were a nevarious module, I would look up the above symbol from
> > kallsyms (it is exported and easily obtainable) and then simply
> > read the text to discover the key address and we're in business.
> >
> 
> Yeah I realised that. So would you prefer to have a
> .static_call_tramp_key section in each module and look up the keys in
> the module loader?

Think so... do you actually have a need for this?