Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN

[Ard Biesheuvel]

On Fri, 15 Apr 2022 at 09:52, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, Apr 15, 2022 at 09:49:12AM +0200, Ard Biesheuvel wrote:
> >
> > I'm not sure I understand what would go wrong if that assumption no
> > longer holds.
>
> It's very simple, we don't do anything to the pointer returned
> by kmalloc before returning it as a tfm or other object with
> an alignment of CRYPTO_MINALIGN.  IOW if kmalloc starts returning
> pointers that are not aligned to CRYPTO_MINALIGN then we'd be
> lying to the compiler.
>

I guess that should be fixable. GIven that this is about padding
rather than alignment, we could do something like

struct crypto_request {
  union {
      struct {
        ... fields ...
      };
      u8 __padding[ARCH_DMA_MINALIGN];
   };
    void __ctx[]  __align(CRYPTO_MINALIGN);
};

And then hopefully, we can get rid of the padding once we fix drivers
doing non-cache coherent inbound DMA into those structures.