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_layout
Fixes: 07f3d789b9be ("Add support for CONFIG_EFI_PARTITION (GUID Partition
Table)")
Signed-off-by: Sam Protsenko <[email protected]>
---
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;
}
/*
