Re: [PATCH v3] mm: Add kvfree_sensitive() for freeing sensitive data objects

[Joe Perches]

On Tue, 2020-04-07 at 16:03 -0400, Waiman Long wrote:
> For kvmalloc'ed data object that contains sensitive information like
> cryptographic key, we need to make sure that the buffer is always
> cleared before freeing it. Using memset() alone for buffer clearing may
> not provide certainty as the compiler may compile it away. To be sure,
> the special memzero_explicit() has to be used.
> 
> This patch introduces a new kvfree_sensitive() for freeing those
> sensitive data objects allocated by kvmalloc(). The relevnat places
> where kvfree_sensitive() can be used are modified to use it.
[]
> diff --git a/include/linux/mm.h b/include/linux/mm.h
[]
> @@ -757,6 +757,7 @@ static inline void *kvcalloc(size_t n, size_t size, gfp_t flags)
>  }
>  
>  extern void kvfree(const void *addr);
> +extern void kvfree_sensitive(const void *addr, size_t len);

Why should size_t len be required?

Why not do what kzfree does and memset
the entire allocation? (area->size)