[PATCH 5/5] arm64: add Crypto Extensions based synchronous core AES cipher

On 30 January 2014 19:56, Will Deacon [off-list ref] wrote:

Hi Ard,

On Wed, Jan 29, 2014 at 04:50:46PM +0000, Ard Biesheuvel wrote:

quoted

diff --git a/arch/arm64/crypto/aes-ce-cipher.c b/arch/arm64/crypto/aes-ce-cipher.c
new file mode 100644
index 000000000000..b5a5d5d6e4b8
--- /dev/null
+++ b/arch/arm64/crypto/aes-ce-cipher.c

@@ -0,0 +1,103 @@
+/*
+ * linux/arch/arm64/crypto/aes-ce-cipher.c
+ *
+ * Copyright (C) 2013 Linaro Ltd <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <asm/neon.h>
+#include <crypto/aes.h>
+#include <linux/crypto.h>
+#include <linux/module.h>
+#include <linux/cpufeature.h>
+
+MODULE_DESCRIPTION("Synchronous AES cipher using ARMv8 Crypto Extensions");
+MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
+MODULE_LICENSE("GPL");
+
+static void aes_cipher_encrypt(struct crypto_tfm *tfm, u8 dst[], u8 const src[])
+{
+     struct crypto_aes_ctx *ctx = crypto_tfm_ctx(tfm);
+     u32 rounds = 6 + ctx->key_length / 4;

Can you document these constants please?

Sure.

quoted

+
+     kernel_neon_begin();
+
+     __asm__("       ld1             {v0.16b}, [%[in]]               ;"
+             "       ld1             {v1.16b}, [%[key]], #16         ;"
+             "0:     aese            v0.16b, v1.16b                  ;"
+             "       subs            %[rounds], %[rounds], #1        ;"
+             "       ld1             {v1.16b}, [%[key]], #16         ;"
+             "       beq             1f                              ;"
+             "       aesmc           v0.16b, v0.16b                  ;"
+             "       b               0b                              ;"
+             "1:     eor             v0.16b, v0.16b, v1.16b          ;"
+             "       st1             {v0.16b}, [%[out]]              ;"
+     : :
+             [out]           "r"(dst),
+             [in]            "r"(src),
+             [rounds]        "r"(rounds),
+             [key]           "r"(ctx->key_enc)
+     :                       "cc");

You probably need a memory output to stop this being re-ordered by the
compiler. Can GCC not generate the addressing modes you need directly,
allowing you to avoid moving everything into registers?

Would a memory clobber work as well?

Re addressing modes: I would prefer to explicitly use v0 and v1, I
have another patch pending that allows partial saves/restores of the
NEON register file when called from interrupt context. I suppose I
could use 'register asm("v0")' or something like that, but that won't
make it any prettier.

quoted

+     kernel_neon_end();
+}
+
+static void aes_cipher_decrypt(struct crypto_tfm *tfm, u8 dst[], u8 const src[])
+{
+     struct crypto_aes_ctx *ctx = crypto_tfm_ctx(tfm);
+     u32 rounds = 6 + ctx->key_length / 4;
+
+     kernel_neon_begin();
+
+     __asm__("       ld1             {v0.16b}, [%[in]]               ;"
+             "       ld1             {v1.16b}, [%[key]], #16         ;"
+             "0:     aesd            v0.16b, v1.16b                  ;"
+             "       ld1             {v1.16b}, [%[key]], #16         ;"
+             "       subs            %[rounds], %[rounds], #1        ;"
+             "       beq             1f                              ;"
+             "       aesimc          v0.16b, v0.16b                  ;"
+             "       b               0b                              ;"
+             "1:     eor             v0.16b, v0.16b, v1.16b          ;"
+             "       st1             {v0.16b}, [%[out]]              ;"
+     : :
+             [out]           "r"(dst),
+             [in]            "r"(src),
+             [rounds]        "r"(rounds),
+             [key]           "r"(ctx->key_dec)
+     :                       "cc");

Same comments here.

FWIW: I spoke to the guy at ARM who designed the crypto instructions and he
reckons your code works :)

Good!

Care to comment on the rest of the series?

Cheers.
Ard.