Re: [PATCH 1/4] crypto: nintendo-aes - add a new AES driver

[Emmanuel Gil Peyrot]

On Wed, Sep 22, 2021 at 12:10:41PM +0200, Ard Biesheuvel wrote:
> On Tue, 21 Sept 2021 at 23:49, Emmanuel Gil Peyrot
> <linkmauve@xxxxxxxxxxxx> wrote:
> >
> > This engine implements AES in CBC mode, using 128-bit keys only.  It is
> > present on both the Wii and the Wii U, and is apparently identical in
> > both consoles.
> >
> > The hardware is capable of firing an interrupt when the operation is
> > done, but this driver currently uses a busy loop, I’m not too sure
> > whether it would be preferable to switch, nor how to achieve that.
> >
> > It also supports a mode where no operation is done, and thus could be
> > used as a DMA copy engine, but I don’t know how to expose that to the
> > kernel or whether it would even be useful.
> >
> > In my testing, on a Wii U, this driver reaches 80.7 MiB/s, while the
> > aes-generic driver only reaches 30.9 MiB/s, so it is a quite welcome
> > speedup.
> >
> > This driver was written based on reversed documentation, see:
> > https://wiibrew.org/wiki/Hardware/AES
> >
> > Signed-off-by: Emmanuel Gil Peyrot <linkmauve@xxxxxxxxxxxx>
> > Tested-by: Emmanuel Gil Peyrot <linkmauve@xxxxxxxxxxxx>  # on Wii U
> 
> This is redundant - everybody should test the code they submit.

Indeed, except for the comment, as I haven’t been able to test on the
Wii just yet and that’s kind of a call for doing exactly that. :)

> 
> ...
> > +       /* TODO: figure out how to use interrupts here, this will probably
> > +        * lower throughput but let the CPU do other things while the AES
> > +        * engine is doing its work. */
> 
> So is it worthwhile like this? How much faster is it to use this
> accelerator rather than the CPU?

As I mentioned above, on my hardware it reaches 80.7 MiB/s using this
busy loop instead of 30.9 MiB/s using aes-generic, measured using
`cryptsetup benchmark --cipher=aes --key-size=128`.  I expect the
difference would be even more pronounced on the Wii, with its CPU being
clocked lower.

I will give a try at using the interrupt, but I fully expect a lower
throughput alongside a lower CPU usage (for large requests).

> 
> > +       do {
> > +               status = ioread32be(base + AES_CTRL);
> > +               cpu_relax();
> > +       } while ((status & AES_CTRL_EXEC) && --counter);
> > +
> > +       /* Do we ever get called with dst ≠ src?  If so we have to invalidate
> > +        * dst in addition to the earlier flush of src. */
> > +       if (unlikely(dst != src)) {
> > +               for (i = 0; i < len; i += 32)
> > +                       __asm__("dcbi 0, %0" : : "r" (dst + i));
> > +               __asm__("sync" : : : "memory");
> > +       }
> > +
> > +       return counter ? 0 : 1;
> > +}
> > +
> > +static void
> > +nintendo_aes_crypt(const void *src, void *dst, u32 len, u8 *iv, int dir,
> > +                  bool firstchunk)
> > +{
> > +       u32 flags = 0;
> > +       unsigned long iflags;
> > +       int ret;
> > +
> > +       flags |= AES_CTRL_EXEC_INIT /* | AES_CTRL_IRQ */ | AES_CTRL_ENA;
> > +
> > +       if (dir == AES_DIR_DECRYPT)
> > +               flags |= AES_CTRL_DEC;
> > +
> > +       if (!firstchunk)
> > +               flags |= AES_CTRL_IV;
> > +
> > +       /* Start the critical section */
> > +       spin_lock_irqsave(&lock, iflags);
> > +
> > +       if (firstchunk)
> > +               writefield(AES_IV, iv);
> > +
> > +       ret = do_crypt(src, dst, len, flags);
> > +       BUG_ON(ret);
> > +
> > +       spin_unlock_irqrestore(&lock, iflags);
> > +}
> > +
> > +static int nintendo_setkey_skcipher(struct crypto_skcipher *tfm, const u8 *key,
> > +                                   unsigned int len)
> > +{
> > +       /* The hardware only supports AES-128 */
> > +       if (len != AES_KEYSIZE_128)
> > +               return -EINVAL;
> > +
> > +       writefield(AES_KEY, key);
> > +       return 0;
> > +}
> > +
> > +static int nintendo_skcipher_crypt(struct skcipher_request *req, int dir)
> > +{
> > +       struct skcipher_walk walk;
> > +       unsigned int nbytes;
> > +       int err;
> > +       char ivbuf[AES_BLOCK_SIZE];
> > +       unsigned int ivsize;
> > +
> > +       bool firstchunk = true;
> > +
> > +       /* Reset the engine */
> > +       iowrite32be(0, base + AES_CTRL);
> > +
> > +       err = skcipher_walk_virt(&walk, req, false);
> > +       ivsize = min(sizeof(ivbuf), walk.ivsize);
> > +
> > +       while ((nbytes = walk.nbytes) != 0) {
> > +               unsigned int chunkbytes = round_down(nbytes, AES_BLOCK_SIZE);
> > +               unsigned int ret = nbytes % AES_BLOCK_SIZE;
> > +
> > +               if (walk.total == chunkbytes && dir == AES_DIR_DECRYPT) {
> > +                       /* If this is the last chunk and we're decrypting, take
> > +                        * note of the IV (which is the last ciphertext block)
> > +                        */
> > +                       memcpy(ivbuf, walk.src.virt.addr + walk.total - ivsize,
> > +                              ivsize);
> > +               }
> > +
> > +               nintendo_aes_crypt(walk.src.virt.addr, walk.dst.virt.addr,
> > +                                  chunkbytes, walk.iv, dir, firstchunk);
> > +
> > +               if (walk.total == chunkbytes && dir == AES_DIR_ENCRYPT) {
> > +                       /* If this is the last chunk and we're encrypting, take
> > +                        * note of the IV (which is the last ciphertext block)
> > +                        */
> > +                       memcpy(walk.iv,
> > +                              walk.dst.virt.addr + walk.total - ivsize,
> > +                              ivsize);
> > +               } else if (walk.total == chunkbytes && dir == AES_DIR_DECRYPT) {
> > +                       memcpy(walk.iv, ivbuf, ivsize);
> > +               }
> > +
> > +               err = skcipher_walk_done(&walk, ret);
> > +               firstchunk = false;
> > +       }
> > +
> > +       return err;
> > +}
> > +
> > +static int nintendo_cbc_encrypt(struct skcipher_request *req)
> > +{
> > +       return nintendo_skcipher_crypt(req, AES_DIR_ENCRYPT);
> > +}
> > +
> > +static int nintendo_cbc_decrypt(struct skcipher_request *req)
> > +{
> > +       return nintendo_skcipher_crypt(req, AES_DIR_DECRYPT);
> > +}
> > +
> > +static struct skcipher_alg nintendo_alg = {
> > +       .base.cra_name          = "cbc(aes)",
> > +       .base.cra_driver_name   = "cbc-aes-nintendo",
> > +       .base.cra_priority      = 400,
> > +       .base.cra_flags         = CRYPTO_ALG_KERN_DRIVER_ONLY,
> > +       .base.cra_blocksize     = AES_BLOCK_SIZE,
> > +       .base.cra_alignmask     = 15,
> > +       .base.cra_module        = THIS_MODULE,
> > +       .setkey                 = nintendo_setkey_skcipher,
> > +       .encrypt                = nintendo_cbc_encrypt,
> > +       .decrypt                = nintendo_cbc_decrypt,
> > +       .min_keysize            = AES_KEYSIZE_128,
> > +       .max_keysize            = AES_KEYSIZE_128,
> > +       .ivsize                 = AES_BLOCK_SIZE,
> > +};
> > +
> > +static int nintendo_aes_remove(struct platform_device *pdev)
> > +{
> > +       struct device *dev = &pdev->dev;
> > +
> > +       crypto_unregister_skcipher(&nintendo_alg);
> > +       devm_iounmap(dev, base);
> > +       base = NULL;
> > +
> > +       return 0;
> > +}
> > +
> > +static int nintendo_aes_probe(struct platform_device *pdev)
> > +{
> > +       struct device *dev = &pdev->dev;
> > +       struct resource *res;
> > +       int ret;
> > +
> > +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +       base = devm_ioremap_resource(dev, res);
> > +       if (IS_ERR(base))
> > +               return PTR_ERR(base);
> > +
> > +       spin_lock_init(&lock);
> > +
> > +       ret = crypto_register_skcipher(&nintendo_alg);
> > +       if (ret)
> > +               goto eiomap;
> > +
> > +       dev_notice(dev, "Nintendo Wii and Wii U AES engine enabled\n");
> > +       return 0;
> > +
> > + eiomap:
> > +       devm_iounmap(dev, base);
> > +
> > +       dev_err(dev, "Nintendo Wii and Wii U AES initialization failed\n");
> > +       return ret;
> > +}
> > +
> > +static const struct of_device_id nintendo_aes_of_match[] = {
> > +       { .compatible = "nintendo,hollywood-aes", },
> > +       { .compatible = "nintendo,latte-aes", },
> > +       {/* sentinel */},
> > +};
> > +MODULE_DEVICE_TABLE(of, nintendo_aes_of_match);
> > +
> > +static struct platform_driver nintendo_aes_driver = {
> > +       .driver = {
> > +               .name = "nintendo-aes",
> > +               .of_match_table = nintendo_aes_of_match,
> > +       },
> > +       .probe = nintendo_aes_probe,
> > +       .remove = nintendo_aes_remove,
> > +};
> > +
> > +module_platform_driver(nintendo_aes_driver);
> > +
> > +MODULE_AUTHOR("Emmanuel Gil Peyrot <linkmauve@xxxxxxxxxxxx>");
> > +MODULE_DESCRIPTION("Nintendo Wii and Wii U Hardware AES driver");
> > +MODULE_LICENSE("GPL");
> > --
> > 2.33.0
> >

-- 
Emmanuel Gil Peyrot

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