From ae686d00fb44cd8d98c64a7b1eae1f26e3b5a215 Mon Sep 17 00:00:00 2001
From: James Bottomley <[email protected]>
Date: Mon, 11 Nov 2024 20:45:47 +0800
Subject: [PATCH 2/2] efi: Add API for retrieving the EFI secret for cryptodisk

cherry-picked from https://mail.gnu.org/archive/html/grub-devel/2022-02/msg00066.html.

This module is designed to provide an efisecret provider which
interrogates the EFI configuration table to find the location of the
confidential computing secret and tries to register the secret with
the cryptodisk.

The secret is stored in a boot allocated area, usually a page in size.
The layout of the secret injection area is a header

|GRUB_EFI_SECRET_TABLE_HEADER_GUID|len|

with entries of the form

|guid|len|data|

the guid corresponding to the disk encryption passphrase is
GRUB_EFI_DISKPASSWD_GUID and data must be a zero terminated string.
To get a high entropy string that doesn't need large numbers of
iterations, use a base64 encoding of 33 bytes of random data.

Signed-off-by: James Bottomley <[email protected]>
Signed-off-by: hanliyang <[email protected]>
---
 grub-core/Makefile.core.def    |   8 ++
 grub-core/disk/efi/efisecret.c | 129 +++++++++++++++++++++++++++++++++
 include/grub/efi/api.h         |  15 ++++
 3 files changed, 152 insertions(+)
 create mode 100644 grub-core/disk/efi/efisecret.c

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index 8c7ba02..d1475c6 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -824,6 +824,14 @@ module = {
   enable = efi;
 };
 
+module = {
+  name = efisecret;
+
+  common = disk/efi/efisecret.c;
+
+  enable = x86_64_efi;
+};
+
 module = {
   name = lsefimmap;
 
diff --git a/grub-core/disk/efi/efisecret.c b/grub-core/disk/efi/efisecret.c
new file mode 100644
index 0000000..1b5bf81
--- /dev/null
+++ b/grub-core/disk/efi/efisecret.c
@@ -0,0 +1,129 @@
+#include <grub/err.h>
+#include <grub/misc.h>
+#include <grub/cryptodisk.h>
+#include <grub/efi/efi.h>
+#include <grub/efi/api.h>
+#include <grub/dl.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+static grub_packed_guid_t secret_guid = GRUB_EFI_SECRET_TABLE_GUID;
+static grub_packed_guid_t tableheader_guid = GRUB_EFI_SECRET_TABLE_HEADER_GUID;
+static grub_packed_guid_t diskpasswd_guid = GRUB_EFI_DISKPASSWD_GUID;
+
+struct efi_secret {
+  grub_uint64_t base;
+  grub_uint64_t size;
+};
+
+struct secret_header {
+  grub_packed_guid_t guid;
+  grub_uint32_t len;
+};
+
+struct secret_entry {
+  grub_packed_guid_t guid;
+  grub_uint32_t len;
+  grub_uint8_t data[0];
+};
+
+static grub_err_t
+grub_efi_secret_put (const char *arg __attribute__((unused)), int have_it,
+                     grub_uint8_t **ptr)
+{
+  struct secret_entry *e = (struct secret_entry *)(*ptr - (long)&((struct secret_entry *)0)->data);
+  int len = e->len;
+
+  /* destroy the secret */
+  grub_memset (e, 0, len);
+  /* put back the length to make sure the table is still traversable */
+  e->len = len;
+
+  *ptr = NULL;
+
+  if (have_it)
+    return GRUB_ERR_NONE;
+
+  return  grub_error (GRUB_ERR_ACCESS_DENIED, "EFI secret failed to unlock any volumes");
+}
+
+static grub_err_t
+grub_efi_secret_find (struct efi_secret *s, grub_uint8_t **secret_ptr)
+{
+  int len;
+  struct secret_header *h;
+  struct secret_entry *e;
+  unsigned char *ptr = (unsigned char *)(unsigned long)s->base;
+
+  /* the area must be big enough for a guid and a u32 length */
+  if (s->size < sizeof (*h))
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI secret area is too small");
+
+  h = (struct secret_header *)ptr;
+  if (grub_memcmp(&h->guid, &tableheader_guid, sizeof (h->guid)))
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI secret area does not start with correct guid\n");
+  if (h->len < sizeof (*h))
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI secret area is too small\n");
+
+  len = h->len - sizeof (*h);
+  ptr += sizeof (*h);
+
+  while (len >= (int)sizeof (*e)) {
+    e = (struct secret_entry *)ptr;
+    if (e->len < sizeof(*e) || e->len > (unsigned int)len)
+      return grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI secret area is corrupt\n");
+
+    if (! grub_memcmp (&e->guid, &diskpasswd_guid, sizeof (e->guid))) {
+      int end = e->len - sizeof(*e);
+
+      /*
+       * the passphrase must be a zero terminated string because the
+       * password routines call grub_strlen () to find its size
+       */
+      if (end < 2 || e->data[end - 1] != '\0')
+       return grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI secret area disk encryption password is corrupt\n");
+
+      *secret_ptr = e->data;
+      return GRUB_ERR_NONE;
+    }
+    ptr += e->len;
+    len -= e->len;
+  }
+  return grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI secret area does not contain disk decryption password\n");
+}
+
+static grub_err_t
+grub_efi_secret_get (const char *arg __attribute__((unused)), grub_uint8_t **ptr)
+{
+  unsigned int i;
+
+  for (i = 0; i < grub_efi_system_table->num_table_entries; i++)
+    {
+      grub_packed_guid_t *guid =
+       &grub_efi_system_table->configuration_table[i].vendor_guid;
+
+      if (! grub_memcmp (guid, &secret_guid, sizeof (grub_packed_guid_t))) {
+       struct efi_secret *s =
+         grub_efi_system_table->configuration_table[i].vendor_table;
+
+       return grub_efi_secret_find(s, ptr);
+      }
+    }
+  return grub_error (GRUB_ERR_BAD_ARGUMENT, "No secret found in the EFI configuration table");
+}
+
+static struct grub_secret_entry secret = {
+  .name = "efisecret",
+  .get = grub_efi_secret_get,
+  .put = grub_efi_secret_put,
+};
+
+GRUB_MOD_INIT(efisecret)
+{
+  grub_cryptodisk_add_secret_provider (&secret);
+}
+
+GRUB_MOD_FINI(efisecret)
+{
+  grub_cryptodisk_remove_secret_provider (&secret);
+}
diff --git a/include/grub/efi/api.h b/include/grub/efi/api.h
index 7947cf5..ccd01c0 100644
--- a/include/grub/efi/api.h
+++ b/include/grub/efi/api.h
@@ -314,6 +314,21 @@
     { 0x9a, 0x16, 0x00, 0x90, 0x27, 0x3f, 0xc1, 0x4d } \
   }
 
+#define GRUB_EFI_SECRET_TABLE_GUID \
+  { 0xadf956ad, 0xe98c, 0x484c, \
+    { 0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47} \
+  }
+
+#define GRUB_EFI_SECRET_TABLE_HEADER_GUID \
+  { 0x1e74f542, 0x71dd, 0x4d66, \
+    { 0x96, 0x3e, 0xef, 0x42, 0x87, 0xff, 0x17, 0x3b } \
+  }
+
+#define GRUB_EFI_DISKPASSWD_GUID \
+  { 0x736869e5, 0x84f0, 0x4973, \
+    { 0x92, 0xec, 0x06, 0x87, 0x9c, 0xe3, 0xda, 0x0b } \
+  }
+
 #define GRUB_EFI_ACPI_TABLE_GUID	\
   { 0xeb9d2d30, 0x2d88, 0x11d3, \
     { 0x9a, 0x16, 0x0, 0x90, 0x27, 0x3f, 0xc1, 0x4d } \
-- 
2.41.1