crypto: arm/aes-neonbs - implement ciphertext stealing for XTS

Update the AES-XTS implementation based on NEON instructions so that it
can deal with inputs whose size is not a multiple of the cipher block
size. This is part of the original XTS specification, but was never
implemented before in the Linux kernel.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

2 files changed, 72 insertions, 13 deletions

diff --git a/arch/arm/crypto/aes-neonbs-core.S b/arch/arm/crypto/aes-neonbs-core.S
index bb75918e4984..cfaed4e67535 100644
--- a/arch/arm/crypto/aes-neonbs-core.S
+++ b/arch/arm/crypto/aes-neonbs-core.S
@@ -889,9 +889,9 @@ ENDPROC(aesbs_ctr_encrypt)
 
         /*
          * aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[], int rounds,
-         *                   int blocks, u8 iv[])
+         *                   int blocks, u8 iv[], int reorder_last_tweak)
          * aesbs_xts_decrypt(u8 out[], u8 const in[], u8 const rk[], int rounds,
-         *                   int blocks, u8 iv[])
+         *                   int blocks, u8 iv[], int reorder_last_tweak)
          */
 __xts_prepare8:
         vld1.8          {q14}, [r7]             // load iv
@@ -944,17 +944,25 @@ __xts_prepare8:
 
         vld1.8          {q7}, [r1]!
         next_tweak      q14, q12, q15, q13
-        veor            q7, q7, q12
+THUMB(  itt             le              )
+        W(cmple)        r8, #0
+        ble             1f
+0:      veor            q7, q7, q12
         vst1.8          {q12}, [r4, :128]
 
-0:      vst1.8          {q14}, [r7]             // store next iv
+        vst1.8          {q14}, [r7]             // store next iv
         bx              lr
+
+1:      vswp            q12, q14
+        b               0b
 ENDPROC(__xts_prepare8)
 
         .macro          __xts_crypt, do8, o0, o1, o2, o3, o4, o5, o6, o7
         push            {r4-r8, lr}
         mov             r5, sp                  // preserve sp
         ldrd            r6, r7, [sp, #24]       // get blocks and iv args
+        ldr             r8, [sp, #32]           // reorder final tweak?
+        rsb             r8, r8, #1
         sub             ip, sp, #128            // make room for 8x tweak
         bic             ip, ip, #0xf            // align sp to 16 bytes
         mov             sp, ip
diff --git a/arch/arm/crypto/aes-neonbs-glue.c b/arch/arm/crypto/aes-neonbs-glue.c
index 9000d0796d5e..e85839a8aaeb 100644
--- a/arch/arm/crypto/aes-neonbs-glue.c
+++ b/arch/arm/crypto/aes-neonbs-glue.c
@@ -12,6 +12,7 @@
 #include <crypto/ctr.h>
 #include <crypto/internal/simd.h>
 #include <crypto/internal/skcipher.h>
+#include <crypto/scatterwalk.h>
 #include <crypto/xts.h>
 #include <linux/module.h>
 
@@ -37,9 +38,9 @@ asmlinkage void aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
                                   int rounds, int blocks, u8 ctr[], u8 final[]);
 
 asmlinkage void aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[],
-                                  int rounds, int blocks, u8 iv[]);
+                                  int rounds, int blocks, u8 iv[], int);
 asmlinkage void aesbs_xts_decrypt(u8 out[], u8 const in[], u8 const rk[],
-                                  int rounds, int blocks, u8 iv[]);
+                                  int rounds, int blocks, u8 iv[], int);
 
 struct aesbs_ctx {
         int     rounds;
@@ -53,6 +54,7 @@ struct aesbs_cbc_ctx {
 
 struct aesbs_xts_ctx {
         struct aesbs_ctx        key;
+        struct crypto_cipher    *cts_tfm;
         struct crypto_cipher    *tweak_tfm;
 };
 
@@ -291,6 +293,9 @@ static int aesbs_xts_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
                 return err;
 
         key_len /= 2;
+        err = crypto_cipher_setkey(ctx->cts_tfm, in_key, key_len);
+        if (err)
+                return err;
         err = crypto_cipher_setkey(ctx->tweak_tfm, in_key + key_len, key_len);
         if (err)
                 return err;
@@ -302,7 +307,13 @@ static int xts_init(struct crypto_tfm *tfm)
 {
         struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
 
+        ctx->cts_tfm = crypto_alloc_cipher("aes", 0, 0);
+        if (IS_ERR(ctx->cts_tfm))
+                return PTR_ERR(ctx->cts_tfm);
+
         ctx->tweak_tfm = crypto_alloc_cipher("aes", 0, 0);
+        if (IS_ERR(ctx->tweak_tfm))
+                crypto_free_cipher(ctx->cts_tfm);
 
         return PTR_ERR_OR_ZERO(ctx->tweak_tfm);
 }
@@ -312,17 +323,34 @@ static void xts_exit(struct crypto_tfm *tfm)
         struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
 
         crypto_free_cipher(ctx->tweak_tfm);
+        crypto_free_cipher(ctx->cts_tfm);
 }
 
-static int __xts_crypt(struct skcipher_request *req,
+static int __xts_crypt(struct skcipher_request *req, bool encrypt,
                        void (*fn)(u8 out[], u8 const in[], u8 const rk[],
-                                  int rounds, int blocks, u8 iv[]))
+                                  int rounds, int blocks, u8 iv[], int))
 {
         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
         struct aesbs_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
+        int tail = req->cryptlen % AES_BLOCK_SIZE;
+        struct skcipher_request subreq;
+        u8 buf[2 * AES_BLOCK_SIZE];
         struct skcipher_walk walk;
         int err;
 
+        if (req->cryptlen < AES_BLOCK_SIZE)
+                return -EINVAL;
+
+        if (unlikely(tail)) {
+                skcipher_request_set_tfm(&subreq, tfm);
+                skcipher_request_set_callback(&subreq,
+                                              skcipher_request_flags(req),
+                                              NULL, NULL);
+                skcipher_request_set_crypt(&subreq, req->src, req->dst,
+                                           req->cryptlen - tail, req->iv);
+                req = &subreq;
+        }
+
         err = skcipher_walk_virt(&walk, req, true);
         if (err)
                 return err;
@@ -331,30 +359,53 @@ static int __xts_crypt(struct skcipher_request *req,
 
         while (walk.nbytes >= AES_BLOCK_SIZE) {
                 unsigned int blocks = walk.nbytes / AES_BLOCK_SIZE;
+                int reorder_last_tweak = !encrypt && tail > 0;
 
-                if (walk.nbytes < walk.total)
+                if (walk.nbytes < walk.total) {
                         blocks = round_down(blocks,
                                             walk.stride / AES_BLOCK_SIZE);
+                        reorder_last_tweak = 0;
+                }
 
                 kernel_neon_begin();
                 fn(walk.dst.virt.addr, walk.src.virt.addr, ctx->key.rk,
-                   ctx->key.rounds, blocks, walk.iv);
+                   ctx->key.rounds, blocks, walk.iv, reorder_last_tweak);
                 kernel_neon_end();
                 err = skcipher_walk_done(&walk,
                                          walk.nbytes - blocks * AES_BLOCK_SIZE);
         }
 
-        return err;
+        if (err || likely(!tail))
+                return err;
+
+        /* handle ciphertext stealing */
+        scatterwalk_map_and_copy(buf, req->dst, req->cryptlen - AES_BLOCK_SIZE,
+                                 AES_BLOCK_SIZE, 0);
+        memcpy(buf + AES_BLOCK_SIZE, buf, tail);
+        scatterwalk_map_and_copy(buf, req->src, req->cryptlen, tail, 0);
+
+        crypto_xor(buf, req->iv, AES_BLOCK_SIZE);
+
+        if (encrypt)
+                crypto_cipher_encrypt_one(ctx->cts_tfm, buf, buf);
+        else
+                crypto_cipher_decrypt_one(ctx->cts_tfm, buf, buf);
+
+        crypto_xor(buf, req->iv, AES_BLOCK_SIZE);
+
+        scatterwalk_map_and_copy(buf, req->dst, req->cryptlen - AES_BLOCK_SIZE,
+                                 AES_BLOCK_SIZE + tail, 1);
+        return 0;
 }
 
 static int xts_encrypt(struct skcipher_request *req)
 {
-        return __xts_crypt(req, aesbs_xts_encrypt);
+        return __xts_crypt(req, true, aesbs_xts_encrypt);
 }
 
 static int xts_decrypt(struct skcipher_request *req)
 {
-        return __xts_crypt(req, aesbs_xts_decrypt);
+        return __xts_crypt(req, false, aesbs_xts_decrypt);
 }
 
 static struct skcipher_alg aes_algs[] = { {