Re: [PATCH 2/2] part: efi: Treat unused partition type GUID as a valid case
On Thu, Mar 28, 2024 at 8:07 PM Heinrich Schuchardt wrote:
>
> 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
> ---- 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
>
> PartStart LBA End LBA Name
> Attributes
> Type GUID
> Partition GUID
>1 0x0800 0x0001f7ff "EFI system partition"
> attrs: 0x0005
> type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b
> (system)
> guid: ee474198-4601-4d5c-81f0-54acf904dd40
>2 0x 0x ""
> attrs: 0x
> type: ----
> (----)
> guid: ----
> ...
>
> 128 0x 0x ""
> attrs: 0x
> type: ----
> (----)
> guid: ----
>
> 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.
>
Thanks for reviewing! In case of Samsung's way of creating GPT tables,
those are actually real partitions (they just "hide" those by means of
setting their type GUIDs to 0), and it's possible to flash those and
interact with them in other ways. But I can see how it's not a
standard way of doing things. And because (as you pointed out) this
patch leads to undesirable effects on other platforms, I also think it
should be NAKed. That of course means it won't be possible to access
all partitions on downstream Samsung devices, but with upstream U-Boot
people will probably want to create an appropriate GPT table anyways.
> Best regards
>
> Heinrich
>
[snip]
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
---- 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
PartStart LBA End LBA Name
Attributes
Type GUID
Partition GUID
1 0x0800 0x0001f7ff "EFI system partition"
attrs: 0x0005
type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b
(system)
guid: ee474198-4601-4d5c-81f0-54acf904dd40
2 0x 0x ""
attrs: 0x
type: ----
(----)
guid: ----
...
128 0x 0x ""
attrs: 0x
type: ----
(----)
guid: ----
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
---
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;
}
/*
[PATCH 2/2] part: efi: Treat unused partition type GUID as a valid case
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)
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).
[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
---
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;
}
/*
--
2.39.2
