Re: [PATCH 06/12] RISC-V: crypto: add accelerated AES-CBC/CTR/ECB/XTS implementations

[Jerry Shih]

On Nov 9, 2023, at 16:05, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> On Thu, Oct 26, 2023 at 02:36:38AM +0800, Jerry Shih wrote:
>> +# prepare input data(v24), iv(v28), bit-reversed-iv(v16), bit-reversed-iv-multiplier(v20)
>> +sub init_first_round {
>> ....
>> +    # Prepare GF(2^128) multiplier [1, x, x^2, x^3, ...] in v8.
>> +    slli $T0, $LEN32, 2
>> +    @{[vsetvli "zero", $T0, "e32", "m1", "ta", "ma"]}
>> +    # v2: [`1`, `1`, `1`, `1`, ...]
>> +    @{[vmv_v_i $V2, 1]}
>> +    # v3: [`0`, `1`, `2`, `3`, ...]
>> +    @{[vid_v $V3]}
>> +    @{[vsetvli "zero", $T0, "e64", "m2", "ta", "ma"]}
>> +    # v4: [`1`, 0, `1`, 0, `1`, 0, `1`, 0, ...]
>> +    @{[vzext_vf2 $V4, $V2]}
>> +    # v6: [`0`, 0, `1`, 0, `2`, 0, `3`, 0, ...]
>> +    @{[vzext_vf2 $V6, $V3]}
>> +    slli $T0, $LEN32, 1
>> +    @{[vsetvli "zero", $T0, "e32", "m2", "ta", "ma"]}
>> +    # v8: [1<<0=1, 0, 0, 0, 1<<1=x, 0, 0, 0, 1<<2=x^2, 0, 0, 0, ...]
>> +    @{[vwsll_vv $V8, $V4, $V6]}
> 
> This code assumes that '1 << i' fits in 64 bits, for 0 <= i < vl.
> 
> I think that works out to an implicit assumption that VLEN <= 2048.  I.e.,
> AES-XTS encryption/decryption would produce the wrong result on RISC-V
> implementations with VLEN > 2048.
> 
> Perhaps it should be explicitly checked that VLEN <= 2048?
> 
> - Eric

Yes, we could just have the simple checking like:

  riscv_vector_vlen() >= 128 || riscv_vector_vlen() <=2048

We could also truncate the VL inside for VLEN>2048 case.
Let me think more about these two approaches. 

-Jerry