From: Ard Biesheuvel <[email protected]>

Loading unauthenticated FDT blobs directly from storage is a security hazard,
so this should only be allowed when running with UEFI Secure Boot disabled.

Signed-off-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Leif Lindholm <[email protected]>
---
 drivers/firmware/efi/arm-stub.c        |    4 +++-
 drivers/firmware/efi/efi-stub-helper.c |   24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/arm-stub.c b/drivers/firmware/efi/arm-stub.c
index b505fde..c651082 100644
--- a/drivers/firmware/efi/arm-stub.c
+++ b/drivers/firmware/efi/arm-stub.c
@@ -95,7 +95,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t 
*sys_table,
 
        /* Load a device tree from the configuration table, if present. */
        fdt_addr = (uintptr_t)get_fdt(sys_table);
-       if (!fdt_addr) {
+       if (efi_secureboot_enabled(sys_table))
+               pr_efi(sys_table, "UEFI Secure Boot is enabled, ignoring dtb= 
commandline option.\n");
+       else if (!fdt_addr) {
                status = handle_cmdline_files(sys_table, image, cmdline_ptr,
                                              "dtb=",
                                              ~0UL, (unsigned long *)&fdt_addr,
diff --git a/drivers/firmware/efi/efi-stub-helper.c 
b/drivers/firmware/efi/efi-stub-helper.c
index 2ee69ea..6221be7 100644
--- a/drivers/firmware/efi/efi-stub-helper.c
+++ b/drivers/firmware/efi/efi-stub-helper.c
@@ -721,3 +721,27 @@ static char *efi_convert_cmdline(efi_system_table_t 
*sys_table_arg,
        *cmd_line_len = options_bytes;
        return (char *)cmdline_addr;
 }
+
+static int __init efi_secureboot_enabled(efi_system_table_t *sys_table_arg)
+{
+       static efi_guid_t const var_guid __initconst = EFI_GLOBAL_VARIABLE_GUID;
+       static efi_char16_t const var_name[] __initconst = {
+               'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0 };
+
+       efi_get_variable_t *f_getvar = sys_table_arg->runtime->get_variable;
+       unsigned long size = sizeof(u8);
+       efi_status_t status;
+       u8 val;
+
+       status = efi_call_phys5(f_getvar, (efi_char16_t *)var_name,
+                               (efi_guid_t *)&var_guid, NULL, &size, &val);
+
+       switch (status) {
+       case EFI_SUCCESS:
+               return val;
+       case EFI_NOT_FOUND:
+               return 0;
+       default:
+               return 1;
+       }
+}
-- 
1.7.10.4

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