Re: [PATCH 2/2] part: efi: Treat unused partition type GUID as a valid case

On 3/28/24 23:29, Sam Protsenko wrote:

Some platforms use the "unused" (all-zero) GUID as a partition type GUID to make some partitions hidden from the OS. For example, Samsung phones and other devices often have GPT partition tables like that, created by their "gpt_builder" tool [1]. All partitions with FILESYS=0 value (second column in [2] file) will be created in a way that:

1. Partition type GUID will be all-zero ("unused")
2. Attributes[48:49] bits will be set to 0 (whereas non-zero values mean the partition is visible to the OS: 1=raw, 2=ext4, 3=f2fs)

The UEFI specification is defining what a GPT partition table has to look like.

According the specification partition type GUID 00000000-0000-0000-0000-000000000000 marks an "unused entry" in the partition table.

An unused partition table entry cannot define a partition. It is one of the entries, that you skip over when enumerating via your patch 1/2.

With this patch 128 partition table entries are printed for an image having a single partition.

=> part list host 0

Partition Map for HOST device 0 -- Partition Type: EFI

Part Start LBA End LBA Name Attributes Type GUID Partition GUID 1 0x00000800 0x0001f7ff "EFI system partition" attrs: 0x0000000000000005 type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b (system) guid: ee474198-4601-4d5c-81f0-54acf904dd40 2 0x00000000 0x00000000 "" attrs: 0x0000000000000000 type: 00000000-0000-0000-0000-000000000000 (00000000-0000-0000-0000-000000000000) guid: 00000000-0000-0000-0000-000000000000 ...

128 0x00000000 0x00000000 "" attrs: 0x0000000000000000 type: 00000000-0000-0000-0000-000000000000 (00000000-0000-0000-0000-000000000000) guid: 00000000-0000-0000-0000-000000000000

This is definitively wrong.

Although it's true that Linux kernel verifies the partition type GUID to be non-zero (in block/partitions/efi.c, is_pte_valid() function), where its U-Boot counterpart code was borrowed from originally, in case of U-Boot we want to handle partitions with "unused" GUIDs the same way as any other valid partitions, to allow the user to interact with those (e.g. list partitions using "part list", be able to flash those via fastboot, etc).

You cannot interact with a non-existing partition.

You may create a new partition in any empty slot that Samsung's tool has left in the partition table and then write to it. No patch is needed for this.

Best regards

Heinrich

[1] https://gitlab.com/Linaro/96boards/e850-96/tools/gpt/ [2] https://gitlab.com/Linaro/96boards/e850-96/tools/gpt/-/blob/master/gpt_layou...

Fixes: 07f3d789b9be ("Add support for CONFIG_EFI_PARTITION (GUID Partition Table)") Signed-off-by: Sam Protsenko semen.protsenko@linaro.org

---

disk/part_efi.c | 21 +++++---------------- 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/disk/part_efi.c b/disk/part_efi.c index 4ce9243ef25c..6b138abae0a6 100644 --- a/disk/part_efi.c +++ b/disk/part_efi.c @@ -1166,28 +1166,17 @@ static gpt_entry *alloc_read_gpt_entries(struct blk_desc *desc, */ static int is_pte_valid(gpt_entry * pte) {

• efi_guid_t unused_guid;

• /*

• * NOTE: Do not check unused (zero) GUIDs here, it's considered a valid
  

• * case in U-Boot.
  

• */
  
  

  if (!pte) { log_debug("Invalid Argument(s)\n"); return 0; }

• /* Only one validation for now:

• * The GUID Partition Type != Unused Entry (ALL-ZERO)
  

• */
  

• memset(unused_guid.b, 0, sizeof(unused_guid.b));
• if (memcmp(pte->partition_type_guid.b, unused_guid.b,

• sizeof(unused_guid.b)) == 0) {
  

• log_debug("Found an unused PTE GUID at 0x%08X\n",
  

• 	  (unsigned int)(uintptr_t)pte);
  

• return 0;
  

• } else {

• return 1;
  

• }

• return 1; }

  /*