[PATCH SLOF 5/5] disk-label: make gpt detection code more robust

[Nikunj A Dadhania]

* Check for Protective MBR Magic
* Check for valid GPT Signature
* Boundary check for allocated block size before reading into the
  buffer

Signed-off-by: Nikunj A Dadhania <nikunj at linux.vnet.ibm.com>
---
 slof/fs/packages/disk-label.fs | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/slof/fs/packages/disk-label.fs b/slof/fs/packages/disk-label.fs
index 821e959..d9c3a8d 100644
--- a/slof/fs/packages/disk-label.fs
+++ b/slof/fs/packages/disk-label.fs
@@ -20,6 +20,7 @@ false VALUE debug-disk-label?
 \ If we ever want to put a large kernel with initramfs from a PREP partition
 \ we might need to increase this value. The default value is 65536 blocks (32MB)
 d# 65536 value max-prep-partition-blocks
+d# 4096 value block-array-size
 
 s" disk-label" device-name
 
@@ -152,8 +153,8 @@ CONSTANT /gpt-part-entry
 : init-block ( -- )
    s" block-size" ['] $call-parent CATCH IF ABORT" parent has no block-size." THEN
    to block-size
-   d# 4096 alloc-mem
-   dup d# 4096 erase
+   block-array-size alloc-mem
+   dup block-array-size erase
    to block
    debug-disk-label? IF
       ." init-block: block-size=" block-size .d ." block=0x" block u. cr
@@ -175,10 +176,18 @@ CONSTANT /gpt-part-entry
    block mbr>magic w at -le aa55 <>
 ;
 
+\
+\ GPT Signature
+\ ("EFI PART", 45h 46h 49h 20h 50h 41h 52h 54h)
+\
+4546492050415254 CONSTANT GPT-SIGNATURE
+
 \ This word returns true if the currently loaded block has _NO_ GPT partition id
 : no-gpt? ( -- true|false )
    0 read-sector
-   1 partition>part-entry part-entry>id c@ ee <>
+   1 partition>part-entry part-entry>id c@ ee <> IF TRUE EXIT THEN
+   block mbr>magic w at -le aa55 <> IF TRUE EXIT THEN
+   1 read-sector block gpt>signature x@ GPT-SIGNATURE <>
 ;
 
 : pc-extended-partition? ( part-entry-addr -- true|false )
@@ -411,6 +420,10 @@ B9E5                CONSTANT GPT-BASIC-DATA-PARTITION-2
    1 read-sector block gpt>part-entry-lba x at -le
    block-size * to seek-pos
    block gpt>part-entry-size l at -le to gpt-part-size
+   gpt-part-size block-array-size > IF
+       cr ." GPT part size exceeds buffer allocated " cr
+       FALSE EXIT
+   THEN
    block gpt>num-part-entry l at -le dup 0= IF FALSE EXIT THEN
    1+ 1 ?DO
       seek-pos 0 seek drop
@@ -646,7 +659,7 @@ B9E5                CONSTANT GPT-BASIC-DATA-PARTITION-2
 
 : close ( -- )
    debug-disk-label? IF ." Closing disk-label: block=0x" block u. ." block-size=" block-size .d cr THEN
-   block d# 4096 free-mem
+   block block-array-size free-mem
 ;
 
 
-- 
1.8.3.1