[PATCH v2 09/15] efi: Add a __efi_data_handoff section annotation

[Jason Gunthorpe <jgg@nvidia.com>]

For a clean DRTM measurement, data written by the stub in the image must
not fall within the measured range. __efi_data_handoff can be used to mark
this data so it is placed outside the measured .data or .init.data
section, and also ensure it is force allocated and not part of .bss.

For DRTM data marked this way will need eventual hardening when the kernel
consumes it. For example sysfb_primary_display eventually leads to a blind
ioremap. Later series will look at hardening these flows.

The arch-agnostic sysfb_primary_display is the first user. The embedded
stub writes it.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/firmware/efi/efi-init.c |  2 +-
 include/linux/efi.h             | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c
index 6103b1a082d247..b00c4c03ca810a 100644
--- a/drivers/firmware/efi/efi-init.c
+++ b/drivers/firmware/efi/efi-init.c
@@ -61,7 +61,7 @@ extern __weak const efi_config_table_type_t efi_arch_tables[];
  * it even without EFI, everything else can get them from here.
  */
 #if !defined(CONFIG_X86) && (defined(CONFIG_SYSFB) || defined(CONFIG_EFI_EARLYCON) || defined(CONFIG_FIRMWARE_EDID))
-struct sysfb_display_info sysfb_primary_display __section(".data");
+struct sysfb_display_info sysfb_primary_display __efi_data_handoff;
 EXPORT_SYMBOL_GPL(sysfb_primary_display);
 #endif
 
diff --git a/include/linux/efi.h b/include/linux/efi.h
index aa15ff88539bdf..a77bb604b1d1fd 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -29,6 +29,18 @@
 
 struct screen_info;
 
+/*
+ * Data the stub wants to pass to the kernel must not land in .bss so it doesn't
+ * get zero'd during early boot, and when DRTM is enabled must not land in the
+ * measured sections. The offset of such data can be passed to both EFI stubs
+ * using a mechanism like struct efi_image_info.
+ */
+#ifdef CONFIG_EFI_STUB_DRTM
+#define __efi_data_handoff	__section(".unmeasured.data")
+#else
+#define __efi_data_handoff	__section(".data")
+#endif
+
 #define EFI_SUCCESS		0
 #define EFI_LOAD_ERROR		( 1 | (1UL << (BITS_PER_LONG-1)))
 #define EFI_INVALID_PARAMETER	( 2 | (1UL << (BITS_PER_LONG-1)))
-- 
2.43.0