[SLOF] [PATCH v3] slof/fs/packages/disk-label.fs: improve checking for DOS boot partitions

[Kautuk Consul]

While testing with a qcow2 with a DOS boot partition it was found that
when we set the logical_block_size in the guest XML to >512 then the
boot would fail in the following interminable loop:
<SNIP>
Trying to load:  from: /pci at 800000020000000/scsi at 3 ... virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
</SNIP>

Change the count-dos-logical-partitions Forth subroutine and the Forth
subroutines calling count-dos-logical-partitions to check for this access
beyond end of device error.

After making the above changes, it fails properly with the correct error
message as follows:
<SNIP>
Trying to load:  from: /pci at 800000020000000/scsi at 3 ... virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!
virtioblk_transfer: Access beyond end of device!

E3404: Not a bootable device!

E3407: Load failed

  Type 'boot' and press return to continue booting the system.
  Type 'reset-all' and press return to reboot the system.

Ready!
0 >
</SNIP>

Signed-off-by: Kautuk Consul <kconsul at linux.ibm.com>
---
 slof/fs/packages/disk-label.fs | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/slof/fs/packages/disk-label.fs b/slof/fs/packages/disk-label.fs
index 661c6b0..fa15982 100644
--- a/slof/fs/packages/disk-label.fs
+++ b/slof/fs/packages/disk-label.fs
@@ -132,11 +132,16 @@ CONSTANT /gpt-part-entry
    debug-disk-label? IF dup ." actual=" .d cr THEN
 ;
 
-\ read sector to array "block"
-: read-sector ( sector-number -- )
+\ read sector to array "block" and return actual bytes read
+: read-sector-ret ( sector-number -- actual-bytes )
    \ block-size is 0x200 on disks, 0x800 on cdrom drives
    block-size * 0 seek drop      \ seek to sector
-   block block-size read drop    \ read sector
+   block block-size read    \ read sector
+;
+
+\ read sector to array "block"
+: read-sector ( sector-number -- )
+   read-sector-ret drop
 ;
 
 : (.part-entry) ( part-entry )
@@ -204,7 +209,8 @@ CONSTANT /gpt-part-entry
          part-entry>sector-offset l at -le    ( current sector )
          dup to part-start to lpart-start  ( current )
          BEGIN
-            part-start read-sector          \ read EBR
+            part-start read-sector-ret          \ read EBR
+            block-size < IF UNLOOP drop 0 EXIT THEN
             1 partition>start-sector IF
                \ ." Logical Partition found at " part-start .d cr
                1+
@@ -279,6 +285,7 @@ CONSTANT /gpt-part-entry
    THEN
 
    count-dos-logical-partitions TO dos-logical-partitions
+   dos-logical-partitions 0= IF false EXIT THEN
 
    debug-disk-label? IF
       ." Found " dos-logical-partitions .d ." logical partitions" cr
@@ -352,6 +359,7 @@ CONSTANT /gpt-part-entry
    no-mbr? IF drop FALSE EXIT THEN  \ read MBR and check for DOS disk-label magic
 
    count-dos-logical-partitions TO dos-logical-partitions
+   dos-logical-partitions 0= IF drop 0 EXIT THEN
 
    debug-disk-label? IF
       ." Found " dos-logical-partitions .d ." logical partitions" cr
-- 
2.31.1