Re: [PATCH] Improve ext2 driver to allow embedding of the boot loader code.

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

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On 09.01.2014 22:07, Dr. Tilmann Bubeck wrote:
> This patch extends the ext2 driver to allow embedding core.img into the
> filesystem. This allows the long needed installation of GRUB into a partition
> without the need to use (unsafe) block lists.
> 
> It is realized using the ioctl(EXT4_IOC_SWAP_BOOT) introduced into
> Linux 3.10. This ioctl basically swaps the data blocks of the associated
> file with the EXT2_BOOT_LOADER_INO inode. After using the ioctl the code
> of core.img is stored in the BOOT_LOADER incode of the filesystem and it
> is not accessible to file system tools anymore. This ensures, that the boot
> code is safe and installation into a partition is possible.
> 
I've already commented on this design here: it not only doesn't
guarantee any kind of blockstability that we need but guarantees quite
the opposite in several scenarios (detailed in previous mails).
> The patchs needs 0001-Refactor-grub_read_mountinfo-out-of-grub_find_root_d.patch
> to work correctly.
> 
> Signed-off-by: Dr. Tilmann Bubeck <tilmann@bubecks.de>
> ---
>  grub-core/fs/ext2.c | 212 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>  util/setup.c        |  11 ++-
>  2 files changed, 215 insertions(+), 8 deletions(-)
> 
> diff --git a/grub-core/fs/ext2.c b/grub-core/fs/ext2.c
> index 5f7a2b9..643969e 100644
> --- a/grub-core/fs/ext2.c
> +++ b/grub-core/fs/ext2.c
> @@ -133,6 +133,14 @@ GRUB_MOD_LICENSE ("GPLv3+");
>  
>  #define EXT4_EXTENTS_FLAG		0x80000
>  
> +/*
> + * Special inodes numbers
> + */
> +#define EXT2_ROOT_INO            2      /* Root inode */
> +#define EXT2_BOOT_LOADER_INO     5      /* Boot loader inode */
> +
> +#define EXT4_IOC_SWAP_BOOT		_IO('f', 17)
> +
>  /* The ext2 superblock.  */
>  struct grub_ext2_sblock
>  {
> @@ -393,10 +401,10 @@ grub_ext4_find_leaf (struct grub_ext2_data *data,
>  }
>  
>  static grub_disk_addr_t
> -grub_ext2_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
> +grub_ext2_read_block2 (struct grub_ext2_data *data,
> +		       struct grub_ext2_inode *inode,
> +		       grub_disk_addr_t fileblock)
>  {
> -  struct grub_ext2_data *data = node->data;
> -  struct grub_ext2_inode *inode = &node->inode;
>    unsigned int blksz = EXT2_BLOCK_SIZE (data);
>    grub_disk_addr_t blksz_quarter = blksz / 4;
>    int log2_blksz = LOG2_EXT2_BLOCK_SIZE (data);
> @@ -497,6 +505,12 @@ indirect:
>    return grub_le_to_cpu32 (indir);
>  }
>  
> +static grub_disk_addr_t
> +grub_ext2_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
> +{
> +  return grub_ext2_read_block2(node->data, &node->inode, fileblock);
> +}
> +
>  /* Read LEN bytes from the file described by DATA starting with byte
>     POS.  Return the amount of read bytes in READ.  */
>  static grub_ssize_t
> @@ -607,12 +621,12 @@ grub_ext2_mount (grub_disk_t disk)
>    data->disk = disk;
>  
>    data->diropen.data = data;
> -  data->diropen.ino = 2;
> +  data->diropen.ino = EXT2_ROOT_INO;
>    data->diropen.inode_read = 1;
>  
>    data->inode = &data->diropen.inode;
>  
> -  grub_ext2_read_inode (data, 2, data->inode);
> +  grub_ext2_read_inode (data, EXT2_ROOT_INO, data->inode);
>    if (grub_errno)
>      goto fail;
>  
> @@ -977,6 +991,193 @@ grub_ext2_mtime (grub_device_t device, grub_int32_t *tm)
>  
>  }
>  
> +#ifdef GRUB_UTIL
> +
> +#include <stdlib.h>
> +#include <sys/ioctl.h>
> +#include <include/grub/emu/misc.h>
> +#include <include/grub/emu/getroot.h>
> +#include <include/grub/emu/hostfile.h>
> +
> +/* Read the addresses of all sectors occupied by the file with the
> +   given inode from the filesystem.  Return the number of sectors in
> +   "nsector" and the addresses in "sectors".  "sectors" is allocated
> +   in this function and must be freed by the caller after usage.
> +   A sector in sectors has size GRUB_DISK_SECTOR_SIZE. */
> +static grub_err_t
> +grub_ext2_read_sectorlist(grub_device_t device,
> +			 int ino,
> +			 unsigned int *nsectors,
> +			 grub_disk_addr_t **sectors)
> +{
> +  struct grub_ext2_data *data;
> +  struct grub_ext2_inode inode;
> +  grub_off_t size;
> +  grub_err_t err;
> +  grub_disk_addr_t fileblock;
> +  int i;
> +  grub_disk_addr_t fileblock_count;
> +  int sectors_per_block;
> +
> +  data = grub_ext2_mount (device->disk);
> +  if (! data) {
> +    return grub_error (grub_errno, N_("Unable to mount device"));
> +  }
> +
> +  err = grub_ext2_read_inode (data, ino, &inode);
> +  if (err)
> +    return grub_error (err, N_("Unable to read inode #%d"), ino);
> +
> +  size = grub_le_to_cpu32 (inode.size);
> +  size |= ((grub_off_t) grub_le_to_cpu32 (inode.size_high)) << 32;
> +
> +  fileblock_count = size / EXT2_BLOCK_SIZE(data);
> +  if ( size % EXT2_BLOCK_SIZE(data) != 0 ) fileblock_count++;
> +
> +  sectors_per_block = EXT2_BLOCK_SIZE(data) / GRUB_DISK_SECTOR_SIZE;
> +  *sectors = grub_malloc (fileblock_count * sectors_per_block
> +			  * sizeof (**sectors));
> +  *nsectors = 0;
> +  for ( fileblock = 0; fileblock < fileblock_count; fileblock++ ) {
> +    (*sectors)[*nsectors] = grub_ext2_read_block2 (data, &inode, fileblock)
> +	                    * sectors_per_block;
> +    for ( i = 1; i < sectors_per_block; i++) {
> +      (*sectors)[(*nsectors) + i] = (*sectors)[*nsectors] + i;
> +    }
> +    (*nsectors) += sectors_per_block;
> +  }
> +
> +  return GRUB_ERR_NONE;
> +}
> +
> +static grub_err_t
> +grub_ext2_embed (grub_device_t device,
> +		  unsigned int *nsectors,
> +		  unsigned int max_nsectors,
> +		  grub_embed_type_t embed_type,
> +		  grub_disk_addr_t **sectors)
> +{
> +  unsigned i;
> +  grub_err_t err;
> +  char *mountpoint;
> +  struct mountinfo_entry *entries;
> +  grub_util_fd_t out;
> +  char *core_name;
> +  char diskbuffer[GRUB_DISK_SECTOR_SIZE];
> +  unsigned int nsectors_wanted;
> +  char *device_name;
> +  int ioctl_err;
> +
> +  if (embed_type != GRUB_EMBED_PCBIOS)
> +    return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
> +		       N_("ext2 currently supports only PC-BIOS embedding"));
> +
> +  if ( device->disk->partition)
> +      device_name = grub_xasprintf ("%s,%s", device->disk->name,
> +			   grub_partition_get_name(device->disk->partition));
> +  else
> +      device_name = grub_xasprintf ("%s", device->disk->name);
> +
> +  nsectors_wanted = *nsectors;
> +
> +  grub_util_info (N_("Embedding %d/%d sectors into ext2 filesystem of %s"),
> +		 nsectors_wanted, max_nsectors, device_name);
> +
> +  /* [1] Check, if the existing boot loader inode exists and has the
> +         wanted size: */
> +  err = grub_ext2_read_sectorlist (device, EXT2_BOOT_LOADER_INO,
> +				   nsectors, sectors);
> +  if (!err && *nsectors >= nsectors_wanted && *nsectors <= max_nsectors) {
> +      grub_util_info(N_("Reusing existing boot loader inode"
> +			" offering %d sectors"),
> +		   *nsectors);
> +    grub_free (device_name);
> +    return GRUB_ERR_NONE;       /* YES! Everything is fine. */
> +  }
> +
> +  /* [2] We have to create a new boot loader inode. */
> +
> +  /* [2.1] Check if device is mounted and get mountpoint: */
> +  mountpoint = NULL;
> +  entries = grub_read_mountinfo ();
> +  if ( entries ) {
> +    for ( i = 0; entries[i].enc_root[0] != 0; i++) {
> +      char *grub_dev_of_mount;
> +      grub_errno = GRUB_ERR_NONE;    /* Clear errno set previously */
> +      grub_dev_of_mount = grub_util_get_grub_dev (entries[i].device);
> +      if ( grub_dev_of_mount ) {
> +	if ( grub_strcmp (grub_dev_of_mount, device_name) == 0 ) {
> +	  mountpoint = grub_strdup (entries[i].enc_path);
> +	  break;
> +	}
> +      }
> +    }
> +    free (entries);
> +  }
> +
> +  grub_errno = GRUB_ERR_NONE;    /* Clear errno set previously */
> +
> +  if (!mountpoint) {
> +    /* We were unable to find the mountpoint for the device of the
> +       filesystem. Maybe it is not mounted? */
> +    return grub_error (GRUB_ERR_UNKNOWN_DEVICE,
> +		       N_("We are unable to find the mountpoint of %s"),
> +		       device_name);
> +
> +    /** ToDo: Try to mount the filesystem to a temporary location. */
> +  }
> +
> +  grub_free (device_name);
> +
> +  /* [2.2] Create a new (temporary) file, which then gets the boot loader: */
> +  core_name = grub_util_path_concat (2, mountpoint, ".core.img");
> +  free (mountpoint);
> +  out = grub_util_fd_open (core_name, GRUB_UTIL_FD_O_WRONLY
> +			   | GRUB_UTIL_FD_O_CREATTRUNC);
> +  if (!GRUB_UTIL_FD_IS_VALID (out)) {
> +    return grub_error (GRUB_ERR_BAD_FS,
> +		       N_("cannot create `%s': %s"), core_name,
> +		       grub_util_fd_strerror ());
> +  }
> +  for ( i = 0; i < max_nsectors; i++ ) {
> +      grub_util_fd_write (out, diskbuffer, GRUB_DISK_SECTOR_SIZE);
> +  }
> +  grub_util_fd_sync (out);
> +
> +  /* [2.3] Make that file to the new boot loader inode by swapping the
> +           file of "out" with the boot loader inode: */
> +  ioctl_err = ioctl (out, EXT4_IOC_SWAP_BOOT);
> +  if ( ioctl_err ) {
> +    err = grub_error (GRUB_ERR_BAD_FS,
> +		      N_("Error in ioctl(EXT4_IOC_SWAP_BOOT);"
> +			 "you need Linux >= 3.10: %s"),
> +		      grub_util_fd_strerror ());
> +    grub_util_fd_close (out);
> +    grub_util_unlink (core_name);
> +    return err;
> +  }
> +  grub_util_fd_close (out);
> +
> +  /* [2.4] Unlink the core file, now containing the previous boot loader. */
> +  grub_util_unlink (core_name);
> +
> +  /* [2.5] Invalidate disk cache and read block list again: */
> +  grub_disk_cache_invalidate_all ();
> +
> +  err = grub_ext2_read_sectorlist (device, EXT2_BOOT_LOADER_INO,
> +				   nsectors, sectors);
> +  if ( err ) {
> +    return grub_error (GRUB_ERR_BAD_FS,
> +		       N_("unable to read boot loader inode"));
> +  }
> +
> +  grub_util_info (N_("Created new boot loader inode offering %d sectors"),
> +		     *nsectors);
> +
> +  return GRUB_ERR_NONE;
> +}
> +#endif
> +
>  
>  \f
>  static struct grub_fs grub_ext2_fs =
> @@ -990,6 +1191,7 @@ static struct grub_fs grub_ext2_fs =
>      .uuid = grub_ext2_uuid,
>      .mtime = grub_ext2_mtime,
>  #ifdef GRUB_UTIL
> +    .embed = grub_ext2_embed,
>      .reserved_first_sector = 1,
>      .blocklist_install = 1,
>  #endif
> diff --git a/util/setup.c b/util/setup.c
> index 9fb91a8..3f4a007 100644
> --- a/util/setup.c
> +++ b/util/setup.c
> @@ -509,8 +509,10 @@ SETUP (const char *dir,
>      if (!err && nsec < core_sectors)
>        {
>  	err = grub_error (GRUB_ERR_OUT_OF_RANGE,
> -			  N_("Your embedding area is unusually small.  "
> -			     "core.img won't fit in it."));
> +			  N_("Your embedding area is unusually small "
> +			     "(only %d sectors). "
> +			     "core.img won't fit in it (needs %d sectors)."),
> +			  nsec, core_sectors);
>        }
>      
>      if (err)
> @@ -583,10 +585,13 @@ SETUP (const char *dir,
>        }
>  
>      /* Write the core image onto the disk.  */
> -    for (i = 0; i < nsec; i++)
> +    for (i = 0; i < nsec; i++) {
> +	grub_util_info ("writing core.img/%d to sector %" PRIuGRUB_UINT64_T, i,
> +			sectors[i]);
>        grub_disk_write (dest_dev->disk, sectors[i], 0,
>  		       GRUB_DISK_SECTOR_SIZE,
>  		       core_img + i * GRUB_DISK_SECTOR_SIZE);
> +    }
>  
>      grub_free (sectors);
>  
> 



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