Re: [PATCH v2 1/3] arm64: crypto/aes-ce-ccm: Cleanup hwcap check

[Suzuki K Poulose]

On 01/11/16 14:03, Ard Biesheuvel wrote:
> Hi Suzuki,
>
> On 31 October 2016 at 16:03, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > Use the module_cpu_feature_match to make sure the system has
> > HWCAP_AES to use the module.
> >
> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> >  arch/arm64/crypto/aes-ce-ccm-glue.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/crypto/aes-ce-ccm-glue.c b/arch/arm64/crypto/aes-ce-ccm-glue.c
> > index f4bf2f2..fa82eaa 100644
> > --- a/arch/arm64/crypto/aes-ce-ccm-glue.c
> > +++ b/arch/arm64/crypto/aes-ce-ccm-glue.c
...
> > -module_init(aes_mod_init);
> > +module_cpu_feature_match(AES, aes_mod_init);
>
> I don't think this change is correct. This will result in the AES
> instruction dependency to be exposed via the module alias, causing the
> module to be loaded automatically as soon as udev detects that the CPU
> implements those instructions. For plain AES, that makes sense, but
> AES in CCM mode is specific to CCMP (WPA2) on mac80211 controllers
> that have no hardware AES support, and to IPsec VPN. For this reason,
> the algo type is exposed via the module alias instead (i.e,
> 'ccm(aes)'), which will result in the module being loaded as soon as
> the crypto algo manager instantiates the transform. On CPUs that don't
> implement the AES instructions, this will fail, and it will fall back
> to the generic CCM driver instead.

Ah, thanks for the explanation. I will drop it.

Cheers
Suzuki