[PATCH] cryptodisk: Properly handle non-512 byte sized sectors.

[Glenn Washburn]

By default, dm-crypt internally uses an IV that corresponds to 512-byte
sectors, even when a larger sector size is specified. What this means is
that when using a larger sector size, the IV is incremented every sector.
However, the amount the IV is incremented is the number of 512 byte blocks
in a sector (ie 8 for 4K sectors). Confusingly the IV does not corespond to
the number of, for example, 4K sectors. So each cipher block in the fifth
4K sector will be encrypted with an IV equal to 32, as opposed to 32-39 for
each sequential 512 byte block or an IV of 4 for each cipher block in the
sector.

There are some encryption utilities which do it the intuitive way and have
the IV equal to the sector number regardless of sector size (ie. the fifth
sector would have an IV of 4 for each cipher block). And this is supported
by dm-crypt with the iv_large_sectors option and also cryptsetup as of 2.3.3
with the --iv-large-sectors, though not with LUKS headers (only with --type
plain). However, support for this has not been included as grub does not
support plain devices right now.

One gotcha here is that the encrypted split keys are encrypted with a hard-
coded 512-byte sector size. So even if your data is encrypted with 4K sector
sizes, the split key encrypted area must be decrypted with a block size of
512 (ie the IV increments every 512 bytes). This made these changes less
aestetically pleasing than desired.

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 grub-core/disk/cryptodisk.c | 44 ++++++++++++++++++++-----------------
 grub-core/disk/luks.c       |  5 +++--
 grub-core/disk/luks2.c      |  7 +++++-
 include/grub/cryptodisk.h   |  9 +++++++-
 4 files changed, 41 insertions(+), 24 deletions(-)

diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
index 0b63b7d96..6319f3164 100644
--- a/grub-core/disk/cryptodisk.c
+++ b/grub-core/disk/cryptodisk.c
@@ -224,7 +224,8 @@ lrw_xor (const struct lrw_sector *sec,
 static gcry_err_code_t
 grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
                           grub_uint8_t * data, grub_size_t len,
-                          grub_disk_addr_t sector, int do_encrypt)
+                          grub_disk_addr_t sector, grub_size_t log_sector_size,
+                          int do_encrypt)
 {
   grub_size_t i;
   gcry_err_code_t err;
@@ -237,12 +238,13 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
     return (do_encrypt ? grub_crypto_ecb_encrypt (dev->cipher, data, data, len)
            : grub_crypto_ecb_decrypt (dev->cipher, data, data, len));
 
-  for (i = 0; i < len; i += (1U << dev->log_sector_size))
+  for (i = 0; i < len; i += (1U << log_sector_size))
     {
       grub_size_t sz = ((dev->cipher->cipher->blocksize
                         + sizeof (grub_uint32_t) - 1)
                        / sizeof (grub_uint32_t));
       grub_uint32_t iv[(GRUB_CRYPTO_MAX_CIPHER_BLOCKSIZE + 3) / 4];
+      grub_uint64_t iv_calc = 0;
 
       if (dev->rekey)
        {
@@ -270,7 +272,7 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
            if (!ctx)
              return GPG_ERR_OUT_OF_MEMORY;
 
-           tmp = grub_cpu_to_le64 (sector << dev->log_sector_size);
+           tmp = grub_cpu_to_le64 (sector << log_sector_size);
            dev->iv_hash->init (ctx);
            dev->iv_hash->write (ctx, dev->iv_prefix, dev->iv_prefix_len);
            dev->iv_hash->write (ctx, &tmp, sizeof (tmp));
@@ -281,14 +283,16 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
          }
          break;
        case GRUB_CRYPTODISK_MODE_IV_PLAIN64:
-         iv[1] = grub_cpu_to_le32 (sector >> 32);
+         iv_calc = sector << (log_sector_size - GRUB_CRYPTODISK_IV_LOG_SIZE);
+         iv[1] = grub_cpu_to_le32 (iv_calc >> 32);
          /* FALLTHROUGH */
        case GRUB_CRYPTODISK_MODE_IV_PLAIN:
-         iv[0] = grub_cpu_to_le32 (sector & 0xFFFFFFFF);
+         iv_calc = sector << (log_sector_size - GRUB_CRYPTODISK_IV_LOG_SIZE);
+         iv[0] = grub_cpu_to_le32 (iv_calc & 0xFFFFFFFF);
          break;
        case GRUB_CRYPTODISK_MODE_IV_BYTECOUNT64:
-         iv[1] = grub_cpu_to_le32 (sector >> (32 - dev->log_sector_size));
-         iv[0] = grub_cpu_to_le32 ((sector << dev->log_sector_size)
+         iv[1] = grub_cpu_to_le32 (sector >> (32 - log_sector_size));
+         iv[0] = grub_cpu_to_le32 ((sector << log_sector_size)
                                    & 0xFFFFFFFF);
          break;
        case GRUB_CRYPTODISK_MODE_IV_BENBI:
@@ -311,10 +315,10 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
        case GRUB_CRYPTODISK_MODE_CBC:
          if (do_encrypt)
            err = grub_crypto_cbc_encrypt (dev->cipher, data + i, data + i,
-                                          (1U << dev->log_sector_size), iv);
+                                          (1U << log_sector_size), iv);
          else
            err = grub_crypto_cbc_decrypt (dev->cipher, data + i, data + i,
-                                          (1U << dev->log_sector_size), iv);
+                                          (1U << log_sector_size), iv);
          if (err)
            return err;
          break;
@@ -322,10 +326,10 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
        case GRUB_CRYPTODISK_MODE_PCBC:
          if (do_encrypt)
            err = grub_crypto_pcbc_encrypt (dev->cipher, data + i, data + i,
-                                           (1U << dev->log_sector_size), iv);
+                                           (1U << log_sector_size), iv);
          else
            err = grub_crypto_pcbc_decrypt (dev->cipher, data + i, data + i,
-                                           (1U << dev->log_sector_size), iv);
+                                           (1U << log_sector_size), iv);
          if (err)
            return err;
          break;
@@ -337,7 +341,7 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
            if (err)
              return err;
            
-           for (j = 0; j < (1U << dev->log_sector_size);
+           for (j = 0; j < (1U << log_sector_size);
                 j += dev->cipher->cipher->blocksize)
              {
                grub_crypto_xor (data + i + j, data + i + j, iv,
@@ -368,11 +372,11 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
            if (do_encrypt)
              err = grub_crypto_ecb_encrypt (dev->cipher, data + i, 
                                             data + i,
-                                            (1U << dev->log_sector_size));
+                                            (1U << log_sector_size));
            else
              err = grub_crypto_ecb_decrypt (dev->cipher, data + i, 
                                             data + i,
-                                            (1U << dev->log_sector_size));
+                                            (1U << log_sector_size));
            if (err)
              return err;
            lrw_xor (&sec, dev, data + i);
@@ -381,10 +385,10 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
        case GRUB_CRYPTODISK_MODE_ECB:
          if (do_encrypt)
            err = grub_crypto_ecb_encrypt (dev->cipher, data + i, data + i,
-                                          (1U << dev->log_sector_size));
+                                          (1U << log_sector_size));
          else
            err = grub_crypto_ecb_decrypt (dev->cipher, data + i, data + i,
-                                          (1U << dev->log_sector_size));
+                                          (1U << log_sector_size));
          if (err)
            return err;
          break;
@@ -399,9 +403,9 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
 gcry_err_code_t
 grub_cryptodisk_decrypt (struct grub_cryptodisk *dev,
                         grub_uint8_t * data, grub_size_t len,
-                        grub_disk_addr_t sector)
+                        grub_disk_addr_t sector, grub_size_t log_sector_size)
 {
-  return grub_cryptodisk_endecrypt (dev, data, len, sector, 0);
+  return grub_cryptodisk_endecrypt (dev, data, len, sector, log_sector_size, 
0);
 }
 
 grub_err_t
@@ -766,7 +770,7 @@ grub_cryptodisk_read (grub_disk_t disk, grub_disk_addr_t 
sector,
     }
   gcry_err = grub_cryptodisk_endecrypt (dev, (grub_uint8_t *) buf,
                                        size << disk->log_sector_size,
-                                       sector, 0);
+                                       sector, dev->log_sector_size, 0);
   return grub_crypto_gcry_error (gcry_err);
 }
 
@@ -807,7 +811,7 @@ grub_cryptodisk_write (grub_disk_t disk, grub_disk_addr_t 
sector,
 
   gcry_err = grub_cryptodisk_endecrypt (dev, (grub_uint8_t *) tmp,
                                        size << disk->log_sector_size,
-                                       sector, 1);
+                                       sector, disk->log_sector_size, 1);
   if (gcry_err)
     {
       grub_free (tmp);
diff --git a/grub-core/disk/luks.c b/grub-core/disk/luks.c
index 59702067a..2e1347b13 100644
--- a/grub-core/disk/luks.c
+++ b/grub-core/disk/luks.c
@@ -124,7 +124,7 @@ configure_ciphers (grub_disk_t disk, const char *check_uuid,
       return NULL;
   newdev->offset = grub_be_to_cpu32 (header.payloadOffset);
   newdev->source_disk = NULL;
-  newdev->log_sector_size = 9;
+  newdev->log_sector_size = LUKS_LOG_SECTOR_SIZE;
   newdev->total_length = grub_disk_get_size (disk) - newdev->offset;
   grub_memcpy (newdev->uuid, uuid, sizeof (uuid));
   newdev->modname = "luks";
@@ -247,7 +247,8 @@ luks_recover_key (grub_disk_t source,
          return err;
        }
 
-      gcry_err = grub_cryptodisk_decrypt (dev, split_key, length, 0);
+      gcry_err = grub_cryptodisk_decrypt (dev, split_key, length, 0,
+                                         LUKS_LOG_SECTOR_SIZE);
       if (gcry_err)
        {
          grub_free (split_key);
diff --git a/grub-core/disk/luks2.c b/grub-core/disk/luks2.c
index 26e1126b1..eb64a0596 100644
--- a/grub-core/disk/luks2.c
+++ b/grub-core/disk/luks2.c
@@ -492,7 +492,12 @@ luks2_decrypt_key (grub_uint8_t *out_key,
       goto err;
     }
 
-  gcry_ret = grub_cryptodisk_decrypt (crypt, split_key, k->area.size, 0);
+  /*
+   * The key slots area is always encrypted in 512-byte sectors,
+   * regardless of encrypted data sector size.
+   */
+  gcry_ret = grub_cryptodisk_decrypt (crypt, split_key, k->area.size, 0,
+                                     LUKS_LOG_SECTOR_SIZE);
   if (gcry_ret)
     {
       ret = grub_crypto_gcry_error (gcry_ret);
diff --git a/include/grub/cryptodisk.h b/include/grub/cryptodisk.h
index e1b21e785..ecb37ba43 100644
--- a/include/grub/cryptodisk.h
+++ b/include/grub/cryptodisk.h
@@ -48,6 +48,13 @@ typedef enum
 
 #define GRUB_CRYPTODISK_MAX_UUID_LENGTH 71
 
+#define LUKS_LOG_SECTOR_SIZE 9
+
+/* For the purposes of IV incrementing the sector size is 512 bytes, unless
+ * otherwise specified.
+ */
+#define GRUB_CRYPTODISK_IV_LOG_SIZE 9
+
 #define GRUB_CRYPTODISK_GF_LOG_SIZE 7
 #define GRUB_CRYPTODISK_GF_SIZE (1U << GRUB_CRYPTODISK_GF_LOG_SIZE)
 #define GRUB_CRYPTODISK_GF_LOG_BYTES (GRUB_CRYPTODISK_GF_LOG_SIZE - 3)
@@ -139,7 +146,7 @@ grub_cryptodisk_setkey (grub_cryptodisk_t dev,
 gcry_err_code_t
 grub_cryptodisk_decrypt (struct grub_cryptodisk *dev,
                         grub_uint8_t * data, grub_size_t len,
-                        grub_disk_addr_t sector);
+                        grub_disk_addr_t sector, grub_size_t log_sector_size);
 grub_err_t
 grub_cryptodisk_insert (grub_cryptodisk_t newdev, const char *name,
                        grub_disk_t source);
-- 
2.27.0