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

Peter Zijlstra
2021-11-09T18:53:18Z

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.