[PATCH v2 2/2] loader/i386/linux: report UEFI secure boot status to the Linux kernel

[Ignat Korchagin]

Linux kernel from 4.11 has secure_boot member as part of linux_kernel_params.
Currently, GRUB does not populate it, so the kernel reports
"Secure boot could not be determined" on boot. We can populate it in EFI mode,
so the kernel "knows" the status.

Signed-off-by: Ignat Korchagin <address@hidden>
---
 grub-core/loader/i386/linux.c | 54 ++++++++++++++++++++++++++++++++++++++++++-
 include/grub/i386/linux.h     | 14 +++++++++--
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/grub-core/loader/i386/linux.c b/grub-core/loader/i386/linux.c
index 4eab55a2d..7016974a6 100644
--- a/grub-core/loader/i386/linux.c
+++ b/grub-core/loader/i386/linux.c
@@ -396,6 +396,57 @@ grub_linux_boot_mmap_fill (grub_uint64_t addr, 
grub_uint64_t size,
   return 0;
 }
 
+#ifdef GRUB_MACHINE_EFI
+
+/* from 
https://github.com/rhboot/shim/blob/b953468e91eac48d2e3817f18cd604e20f39c56b/lib/guid.c#L39
 */
+#define GRUB_EFI_SHIM_LOCK_GUID \
+  { 0x605dab50, 0xe046, 0xe046, { 0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 
0x23 }}
+
+/* mostly taken from 
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/firmware/efi/libstub/secureboot.c?h=linux-4.18.y&id=a7012bdbdf406bbaa4e3de0cc3d8eb0faaacbf93#n37
+   except for the case, when "SecureBoot" variable is not found, because
+   grub_efi_get_variable does not report EFI_STATUS to the caller */
+static grub_uint8_t
+grub_efi_secureboot_mode (void)
+{
+  grub_efi_guid_t efi_var_guid = GRUB_EFI_GLOBAL_VARIABLE_GUID;
+  grub_size_t efi_var_size = 0;
+  grub_efi_uint32_t attr = 0;
+  grub_uint8_t *secure_boot;
+  grub_uint8_t *setup_mode;
+  grub_uint8_t *moksb_state;
+  grub_uint8_t secureboot_mode = LINUX_EFI_SECUREBOOT_MODE_UNKNOWN;
+
+  secure_boot = grub_efi_get_variable ("SecureBoot", &efi_var_guid, 
&efi_var_size);
+  setup_mode = grub_efi_get_variable ("SetupMode", &efi_var_guid, 
&efi_var_size);
+  efi_var_guid = GRUB_EFI_SHIM_LOCK_GUID;
+  moksb_state = grub_efi_get_variable_with_attributes ("MokSBState", 
&efi_var_guid, &efi_var_size, &attr);
+
+  if (!secure_boot || !setup_mode)
+    goto fail;
+
+  if ((*secure_boot == 0) || (*setup_mode == 1))
+    secureboot_mode = LINUX_EFI_SECUREBOOT_MODE_DISABLED;
+  else
+    secureboot_mode = LINUX_EFI_SECUREBOOT_MODE_ENABLED;
+
+  if (moksb_state)
+    {
+      if (!(attr & GRUB_EFI_VARIABLE_RUNTIME_ACCESS) && *moksb_state == 1)
+        secureboot_mode = LINUX_EFI_SECUREBOOT_MODE_DISABLED;
+    }
+
+fail:
+  if (moksb_state)
+    grub_free (moksb_state);
+  if (setup_mode)
+    grub_free (setup_mode);
+  if (secure_boot)
+    grub_free (secure_boot);
+
+  return secureboot_mode;
+}
+#endif
+
 static grub_err_t
 grub_linux_boot (void)
 {
@@ -574,6 +625,7 @@ grub_linux_boot (void)
     grub_efi_uintn_t efi_desc_size;
     grub_size_t efi_mmap_target;
     grub_efi_uint32_t efi_desc_version;
+    ctx.params->secure_boot = grub_efi_secureboot_mode ();
     err = grub_efi_finish_boot_services (&efi_mmap_size, efi_mmap_buf, NULL,
                                         &efi_desc_size, &efi_desc_version);
     if (err)
@@ -760,7 +812,7 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
 
   linux_params.code32_start = prot_mode_target + lh.code32_start - 
GRUB_LINUX_BZIMAGE_ADDR;
   linux_params.kernel_alignment = (1 << align);
-  linux_params.ps_mouse = linux_params.padding10 =  0;
+  linux_params.ps_mouse = linux_params.padding11 =  0;
 
   len = sizeof (linux_params) - sizeof (lh);
   if (grub_file_read (file, (char *) &linux_params + sizeof (lh), len) != len)
diff --git a/include/grub/i386/linux.h b/include/grub/i386/linux.h
index 60c7c3b5e..4d20abb2e 100644
--- a/include/grub/i386/linux.h
+++ b/include/grub/i386/linux.h
@@ -87,6 +87,12 @@ enum
     GRUB_VIDEO_LINUX_TYPE_SIMPLE = 0x70    /* Linear framebuffer without any 
additional functions.  */
   };
 
+/* Possible values for Linux secure_boot kernel parameter */
+#define LINUX_EFI_SECUREBOOT_MODE_UNSET    0
+#define LINUX_EFI_SECUREBOOT_MODE_UNKNOWN  1
+#define LINUX_EFI_SECUREBOOT_MODE_DISABLED 2
+#define LINUX_EFI_SECUREBOOT_MODE_ENABLED  3
+
 /* For the Linux/i386 boot protocol version 2.10.  */
 struct linux_i386_kernel_header
 {
@@ -270,7 +276,11 @@ struct linux_kernel_params
 
   grub_uint8_t mmap_size;              /* 1e8 */
 
-  grub_uint8_t padding9[0x1f1 - 0x1e9];
+  grub_uint8_t padding9[0x1ec - 0x1e9];
+
+  grub_uint8_t secure_boot;             /* 1ec */
+
+  grub_uint8_t padding10[0x1f1 - 0x1ed];
 
   grub_uint8_t setup_sects;            /* The size of the setup in sectors */
   grub_uint16_t root_flags;            /* If the root is mounted readonly */
@@ -280,7 +290,7 @@ struct linux_kernel_params
   grub_uint16_t vid_mode;              /* Video mode control */
   grub_uint16_t root_dev;              /* Default root device number */
 
-  grub_uint8_t padding10;              /* 1fe */
+  grub_uint8_t padding11;              /* 1fe */
   grub_uint8_t ps_mouse;               /* 1ff */
 
   grub_uint16_t jump;                  /* Jump instruction */
-- 
2.11.0