[PATCH v35 14/14] efi/libstub/arm*: Set default address and size cells values for an empty dtb

[takahiro.akashi@linaro.org (AKASHI Takahiro)]

From: Sameer Goel <sgoel@codeaurora.org>

In cases where a device tree is not provided (ie ACPI based system), an
empty fdt is generated by efistub.  #address-cells and #size-cells are not
set in the empty fdt, so they default to 1 (4 byte wide).  This can be an
issue on 64-bit systems where values representing addresses, etc may be
8 bytes wide as the default value does not align with the general
requirements for an empty DTB, and is fragile when passed to other agents
as extra care is required to read the entire width of a value.

This issue is observed on Qualcomm Technologies QDF24XX platforms when
kexec-tools inserts 64-bit addresses into the "linux,elfcorehdr" and
"linux,usable-memory-range" properties of the fdt.  When the values are
later consumed, they are truncated to 32-bit.

Setting #address-cells and #size-cells to 2 at creation of the empty fdt
resolves the observed issue, and makes the fdt less fragile.

Signed-off-by: Sameer Goel <sgoel@codeaurora.org>
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 drivers/firmware/efi/libstub/fdt.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
index 260c4b4b492e..82973b86efe4 100644
--- a/drivers/firmware/efi/libstub/fdt.c
+++ b/drivers/firmware/efi/libstub/fdt.c
@@ -16,6 +16,22 @@
 
 #include "efistub.h"
 
+#define EFI_DT_ADDR_CELLS_DEFAULT 2
+#define EFI_DT_SIZE_CELLS_DEFAULT 2
+
+static void fdt_update_cell_size(efi_system_table_t *sys_table, void *fdt)
+{
+	int offset;
+
+	offset = fdt_path_offset(fdt, "/");
+	/* Set the #address-cells and #size-cells values for an empty tree */
+
+	fdt_setprop_u32(fdt, offset, "#address-cells",
+			EFI_DT_ADDR_CELLS_DEFAULT);
+
+	fdt_setprop_u32(fdt, offset, "#size-cells", EFI_DT_SIZE_CELLS_DEFAULT);
+}
+
 static efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
 			       unsigned long orig_fdt_size,
 			       void *fdt, int new_fdt_size, char *cmdline_ptr,
@@ -42,10 +58,18 @@ static efi_status_t update_fdt(efi_system_table_t *sys_table, void *orig_fdt,
 		}
 	}
 
-	if (orig_fdt)
+	if (orig_fdt) {
 		status = fdt_open_into(orig_fdt, fdt, new_fdt_size);
-	else
+	} else {
 		status = fdt_create_empty_tree(fdt, new_fdt_size);
+		if (status == 0) {
+			/*
+			 * Any failure from the following function is non
+			 * critical
+			 */
+			fdt_update_cell_size(sys_table, fdt);
+		}
+	}
 
 	if (status != 0)
 		goto fdt_set_fail;
-- 
2.11.1