[PATCH] fs: efivarfs: allow creating variables under any GUID in loader mode

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

efivars_create() refuses to create variables outside the barebox vendor
GUID. That dates from when barebox was only an EFI payload: on somebody
else's firmware, whose NVRAM holds the platform's own state, a shell that
can create Boot#### or BootOrder under the global GUID is a liability,
and the payload only ever needs barebox-env-<guid> anyway.

The EFI loader took the same efivarfs over unchanged, where the argument
does not hold. The store is barebox' own in-memory buffer backed by a
file it writes itself, and everything the loader starts - the UEFI
Shell, GRUB, the OS - can already create variables under any GUID. Only
the barebox shell was held back:

  barebox:/ echo -o /efivarfs/Timeout-8be4df61-93ca-11d2-aa0d-00e098032b8c 5
  open: Operation not permitted

Lift the restriction when running as the loader, so board scripts can
set up global variables without going through /env/data/init.efivars.
The payload keeps confining itself to its own GUID.

Assisted-by: Claude:opus-5
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 fs/efivarfs.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/efivarfs.c b/fs/efivarfs.c
index a4d8cc8d0268..1f53c06d66d3 100644
--- a/fs/efivarfs.c
+++ b/fs/efivarfs.c
@@ -66,12 +66,17 @@ static int efivars_create(struct device *dev, const char *pathname,
 	if (pathname[0] == '/')
 		pathname++;
 
-	/* deny creating files with other vendor GUID than our own */
 	ret = efivarfs_parse_filename(pathname, &vendor, &name);
 	if (ret)
 		return -ENOENT;
 
-	if (efi_guidcmp(vendor, EFI_BAREBOX_VENDOR_GUID))
+	/*
+	 * As a payload, barebox is a guest on somebody else's firmware and
+	 * confines itself to its own vendor GUID when creating variables.
+	 * As the loader, the variable store is barebox' own and anything it
+	 * boots may already create variables under any GUID.
+	 */
+	if (!efi_is_loader() && efi_guidcmp(vendor, EFI_BAREBOX_VENDOR_GUID))
 		return -EPERM;
 
 	inode = xzalloc(sizeof(*inode));
-- 
2.47.3