[PATCH] efidisk: Respect block_io_protocol buffer alignment

[Leif Lindholm]

Returned from the OpenProtocol operation, the grub_efi_block_io_media
structure contains the io_align field, specifying the minimum alignment
required for buffers used in any data transfers with the device.

Make grub_efidisk_readwrite() allocate a temporary buffer, aligned to
this boundary, if the buffer passed to it does not already meet the
requirements.

Reported-by: Jeremy Linton <address@hidden>
---

This modified version is contained entirely within the efidisk driver.
There is some excessive copying going on, but it removes the risk of
the changes interfering with other disk drivers.

 grub-core/disk/efi/efidisk.c | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/grub-core/disk/efi/efidisk.c b/grub-core/disk/efi/efidisk.c
index 1c00e3e..901133f 100644
--- a/grub-core/disk/efi/efidisk.c
+++ b/grub-core/disk/efi/efidisk.c
@@ -524,15 +524,42 @@ grub_efidisk_readwrite (struct grub_disk *disk, 
grub_disk_addr_t sector,
 {
   struct grub_efidisk_data *d;
   grub_efi_block_io_t *bio;
+  grub_efi_status_t status;
+  grub_size_t io_align, num_bytes;
+  char *aligned_buf;
 
   d = disk->data;
   bio = d->block_io;
 
-  return efi_call_5 ((wr ? bio->write_blocks : bio->read_blocks), bio,
-                    bio->media->media_id,
-                    (grub_efi_uint64_t) sector,
-                    (grub_efi_uintn_t) size << disk->log_sector_size,
-                    buf);
+  /* Set alignment to 1 if 0 specified */
+  io_align = bio->media->io_align ? bio->media->io_align : 1;
+  num_bytes = size << disk->log_sector_size;
+
+  if ((unsigned long) buf & (io_align - 1))
+    {
+      aligned_buf = grub_memalign (io_align, num_bytes);
+      if (! aligned_buf)
+       return GRUB_EFI_OUT_OF_RESOURCES;
+      if (wr)
+       grub_memcpy (aligned_buf, buf, num_bytes);
+    }
+  else
+    {
+      aligned_buf = buf;
+    }
+
+  status =  efi_call_5 ((wr ? bio->write_blocks : bio->read_blocks), bio,
+                       bio->media->media_id, (grub_efi_uint64_t) sector,
+                       (grub_efi_uintn_t) num_bytes, aligned_buf);
+
+  if ((unsigned long) buf & (io_align - 1))
+    {
+      if (!wr)
+       grub_memcpy (buf, aligned_buf, num_bytes);
+      grub_free (aligned_buf);
+    }
+
+  return status;
 }
 
 static grub_err_t
-- 
2.1.4