[llvmlinux] VLAIS cleanup

[PaX Team]

On 24 Mar 2014 at 15:45, Renato Golin wrote:

> function_whatever(arguments) {
>   struct {
>     struct shash_desc desc;
>     char ctx[crypto_shash_descsize(lmk->hash_tfm)];
>   } sdesc;
>   ...
>   // sometimes...
>   ctx = ...;
> 
>   // always
>   whatever = another_function(&sdesc.desc, ...);
> 
>   // sometimes, less often
>   return ctx;
> }
> 
> I'm not a kernel expert, but I couldn't find any of those functions
> receiving the address of the first member modifying anything past the
> sizeof(desc), which is the only way it could be using the ctx member
> without clearly stated in the code.

note the last field in struct shash_desc: void *__ctx[] CRYPTO_MINALIGN_ATTR;

what the various callbacks in shash_alg structs do is that they call shash_desc_ctx()
to convert the shash_desc ptr into the ctx ptr: return desc->__ctx;