[PATCH v3 08/12] asm-generic: Refactor dereference_[kernel]_function_descriptor()

[Christophe Leroy]

Le 11/02/2022 à 01:56, Kees Cook a écrit :
> On Thu, Feb 10, 2022 at 09:30:43PM +1100, Michael Ellerman wrote:
>> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
>>> diff --git a/kernel/extable.c b/kernel/extable.c
>>> index b0ea5eb0c3b4..1ef13789bea9 100644
>>> --- a/kernel/extable.c
>>> +++ b/kernel/extable.c
>>> @@ -159,12 +160,32 @@ int kernel_text_address(unsigned long addr)
>>>   }
>>>   
>>>   /*
>>> - * On some architectures (PPC64, IA64) function pointers
>>> + * On some architectures (PPC64, IA64, PARISC) function pointers
>>>    * are actually only tokens to some data that then holds the
>>>    * real function address. As a result, to find if a function
>>>    * pointer is part of the kernel text, we need to do some
>>>    * special dereferencing first.
>>>    */
>>> +#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
>>> +void *dereference_function_descriptor(void *ptr)
>>> +{
>>> +	func_desc_t *desc = ptr;
>>> +	void *p;
>>> +
>>> +	if (!get_kernel_nofault(p, (void *)&desc->addr))
>>> +		ptr = p;
>>> +	return ptr;
>>> +}
>>
>> This needs an EXPORT_SYMBOL_GPL(), otherwise the build breaks after
>> patch 10 with CONFIG_LKDTM=m.
> 
> Oh good catch!
> 
> (There have been a few cases of LKDTM=m being the only thing needed a
> symbol, so I've pondered giving it a namespace or constructing a little
> ifdef wrapper... but this seems ok to export...)
> 

powerpc and ia64 had it as a static inline, but parisc had it as a plain 
function and didn't export it. So I guess the export is not required at 
this point. I will export it in patch 10 when it becomes necessary.

Christophe