Re: [PATCH v2 04/13] RISC-V: crypto: add Zvkned accelerated AES implementation

[Eric Biggers]

On Tue, Nov 28, 2023 at 12:22:26PM +0800, Jerry Shih wrote:
> On Nov 28, 2023, at 11:56, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> > On Mon, Nov 27, 2023 at 03:06:54PM +0800, Jerry Shih wrote:
> >> +int riscv64_aes_setkey(struct crypto_aes_ctx *ctx, const u8 *key,
> >> +		       unsigned int keylen)
> >> +{
> >> +	int ret;
> >> +
> >> +	ret = aes_check_keylen(keylen);
> >> +	if (ret < 0)
> >> +		return -EINVAL;
> >> +
> >> +	/*
> >> +	 * The RISC-V AES vector crypto key expanding doesn't support AES-192.
> >> +	 * Use the generic software key expanding for that case.
> >> +	 */
> >> +	if ((keylen == 16 || keylen == 32) && crypto_simd_usable()) {
> >> +		/*
> >> +		 * All zvkned-based functions use encryption expanding keys for both
> >> +		 * encryption and decryption.
> >> +		 */
> >> +		kernel_vector_begin();
> >> +		rv64i_zvkned_set_encrypt_key(key, keylen, ctx);
> >> +		kernel_vector_end();
> >> +	} else {
> >> +		ret = aes_expandkey(ctx, key, keylen);
> >> +	}
> > 
> > rv64i_zvkned_set_encrypt_key() does not initialize crypto_aes_ctx::key_dec.
> > So, decryption results will be incorrect if !crypto_simd_usable() later.
> 
> Will we have the situation that `crypto_simd_usable()` condition is not consistent
> during the aes_setkey(), aes_enc/dec()? If yes, all accelerated(or HW specific)
> crypto algorithms should do the same implementations as the sw fallback path
> since the `crypto_simd_usable()` will change back and forth.

Yes, the calls to one "crypto_cipher" can happen in different contexts.  For
example, crypto_simd_usable() can be true during setkey and false during
decrypt, or vice versa.

If the RISC-V decryption code wants to use the regular key schedule (key_enc)
instead of the "Equivalent Inverse Cipher key schedule" (key_dec), that's
perfectly fine, but setkey still needs to initialize key_dec in case the
fallback to aes_decrypt() gets taken.

> >> diff --git a/arch/riscv/crypto/aes-riscv64-zvkned.pl b/arch/riscv/crypto/aes-riscv64-zvkned.pl
> >> new file mode 100644
> >> index 000000000000..303e82d9f6f0
> >> --- /dev/null
> >> +++ b/arch/riscv/crypto/aes-riscv64-zvkned.pl
> > [...]
> >> +L_enc_128:
> > [...]
> >> +L_enc_192:
> > [...]
> >> +L_enc_256:
> > 
> > There's some severe source code duplication going on in the AES assembly, with
> > the three AES variants having separate source code.  You can just leave this
> > as-is since this is what was merged into OpenSSL and we are borrowing that for
> > now, but I do expect that we'll want to clean this up later.
> 
> Do we prefer the code with the branches instead of the specified implementation?
> We could make AES-128/192/256 together like:
> 
>     @{[vaesz_vs $V24, $V1]}
>     @{[vaesem_vs $V24, $V2]}
>     @{[vaesem_vs $V24, $V3]}
>     @{[vaesem_vs $V24, $V4]}
>     @{[vaesem_vs $V24, $V5]}
>     @{[vaesem_vs $V24, $V6]}
>     @{[vaesem_vs $V24, $V7]}
>     @{[vaesem_vs $V24, $V8]}
>     @{[vaesem_vs $V24, $V9]}
>     @{[vaesem_vs $V24, $V10]}
>     beq $ROUND, $ROUND_11, 1f
>     @{[vaesem_vs $V24, $V11]}
>     @{[vaesem_vs $V24, $V12]}
>     beq $ROUND, $ROUND_13, 1f
>     @{[vaesem_vs $V24, $V13]}
>     @{[vaesem_vs $V24, $V14]}
> 1:
>     @{[vaesef_vs $V24, $V15]}
> 
> But we will have the additional costs for the branches.
> 

That needs to be decided on a case by case basis depending on the performance
impact and how much binary code is saved.  On some architectures, separate
binary code for AES-{128,192,256} has been found to be worthwhile.  However,
that does *not* mean that they need to have separate source code.  Take a look
at how arch/x86/crypto/aes_ctrby8_avx-x86_64.S generates code for all the AES
variants using macros, for example.

Anyway, I don't think you should bother making too many changes to the "perlasm"
files.  If we decide to make major cleanups I think we should just replace them
with .S files (which already support macros).

- Eric