OvmfPkg/AmdSev: add Grub Firmware Volume Package

This is used to package up the grub bootloader into a firmware volume
where it can be executed as a shell like the UEFI Shell.  Grub itself
is built as a minimal entity into a Fv and then added as a boot
option.  By default the UEFI shell isn't built but for debugging
purposes it can be enabled and will then be presented as a boot option
(This should never be allowed for secure boot in an external data
centre but may be useful for local debugging).  Finally all other boot
options except grub and possibly the shell are stripped and the boot
timeout forced to 0 so the system will not enter a setup menu and will
only boot to grub.  This is done by copying the
Library/PlatformBootManagerLib into Library/PlatformBootManagerLibGrub
and then customizing it.

Boot failure is fatal to try to prevent secret theft.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3077
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Message-Id: <20201130202819.3910-4-jejb@linux.ibm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
[lersek@redhat.com: replace local variable initialization with assignment]
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
[lersek@redhat.com: squash 'OvmfPkg: add "gGrubFileGuid=Grub" to
 GuidCheck.IgnoreDuplicates', reviewed stand-alone by Phil (msgid
 <e6eae551-8563-ccfb-5547-7a97da6d46e5@redhat.com>) and Ard (msgid
 <10aeda37-def6-d9a4-6e02-4c66c1492f57@arm.com>)]

4 files changed, 179 insertions, 0 deletions

diff --git a/OvmfPkg/AmdSev/Grub/.gitignore b/OvmfPkg/AmdSev/Grub/.gitignore
new file mode 100644
index 0000000..779a865
--- /dev/null
+++ b/OvmfPkg/AmdSev/Grub/.gitignore
@@ -0,0 +1 @@
+grub.efi

diff --git a/OvmfPkg/AmdSev/Grub/Grub.inf b/OvmfPkg/AmdSev/Grub/Grub.inf
new file mode 100644
index 0000000..90dc6c7
--- /dev/null
+++ b/OvmfPkg/AmdSev/Grub/Grub.inf
@@ -0,0 +1,39 @@
+##  @file

+#  Create a Firmware Volume based Grub Bootloader

+#

+#  Copyright (C) 2020 James Bottomley, IBM Corporation.

+#

+#  SPDX-License-Identifier: BSD-2-Clause-Patent

+#

+##

+

+[Defines]

+  INF_VERSION                    = 0x00010006

+  BASE_NAME                      = Grub

+  # This is gGrubFileGuid

+  FILE_GUID                      = b5ae312c-bc8a-43b1-9c62-ebb826dd5d07

+  MODULE_TYPE                    = UEFI_APPLICATION

+  VERSION_STRING                 = 1.0

+  ENTRY_POINT                    = UefiMain

+

+[Packages]

+  OvmfPkg/OvmfPkg.dec

+

+#

+# The following information is for reference only and not required by

+# the build tools.

+#

+#  VALID_ARCHITECTURES           = X64

+#

+

+##

+# Note: The version of grub.efi this picks up can be generated by

+# grub.sh which must be specified as a PREBUILD in the .dsc file. If

+# grub.efi is newer than either grub.sh or grub.cfg then grub.sh will

+# exit with success meaning that if you move your own version of grub

+# in here (after checking out grub.sh and grub.cfg), PREBUILD won't

+# overwrite it.

+##

+[Binaries]

+   PE32|grub.efi|*

+

diff --git a/OvmfPkg/AmdSev/Grub/grub.cfg b/OvmfPkg/AmdSev/Grub/grub.cfg
new file mode 100644
index 0000000..17be942
--- /dev/null
+++ b/OvmfPkg/AmdSev/Grub/grub.cfg
@@ -0,0 +1,46 @@
+##  @file

+#  Execute a script to recover the SEV supplied secret and use it to

+#  decrypt a luks volume.  For security, the kernel must be on an encrypted

+#  volume so reboot if none are found.

+#

+#  Copyright (C) 2020 James Bottomley, IBM Corporation.

+#

+#  SPDX-License-Identifier: BSD-2-Clause-Patent

+#

+##

+

+echo "Entering grub config"

+sevsecret

+if [ $? -ne 0 ]; then

+    echo "Failed to locate anything in the SEV secret area, prompting for password"

+    cryptomount -a

+else

+    cryptomount -s

+    if [ $? -ne 0 ]; then

+        echo "Failed to mount root securely, retrying with password prompt"

+        cryptomount -a

+    fi

+fi

+set root=

+for f in (crypto*); do

+    if [ -e $f/boot/grub/grub.cfg ]; then

+        set root=$f

+        set prefix=($root)/boot/grub

+        break;

+    fi

+done

+if [ x$root = x ]; then

+    echo "Failed to find any grub configuration on the encrypted volume"

+    sleep 5

+    reboot

+fi

+# rest of modules to get boot to work

+set modules="

+    boot

+    loadenv

+    "

+for f in $modules; do

+    insmod $f

+done

+echo "Transferring to ${prefix}/grub.cfg"

+source $prefix/grub.cfg

diff --git a/OvmfPkg/AmdSev/Grub/grub.sh b/OvmfPkg/AmdSev/Grub/grub.sh
new file mode 100644
index 0000000..99807d7
--- /dev/null
+++ b/OvmfPkg/AmdSev/Grub/grub.sh
@@ -0,0 +1,93 @@
+##  @file
+#  Build a version of grub capable of decrypting a luks volume with a SEV
+#  Supplied secret
+#
+#  Copyright (C) 2020 James Bottomley, IBM Corporation.
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+set -e
+remove_efi=1
+
+cleanup()  {
+    # remove the intermediates
+    for f in disk.fat grub-bootstrap.cfg; do
+        rm -f -- "${basedir}/$f"
+    done
+    if [ $remove_efi -eq 1 ]; then
+        rm -f -- "${basedir}/grub.efi"
+    fi
+}
+
+trap cleanup EXIT
+
+GRUB_MODULES="
+            part_msdos
+            part_gpt
+            cryptodisk
+            luks
+            gcry_rijndael
+            gcry_sha256
+            ext2
+            btrfs
+            xfs
+            fat
+            configfile
+            memdisk
+            sleep
+            normal
+            echo
+            test
+            regexp
+            linux
+            linuxefi
+            reboot
+            sevsecret
+            "
+basedir=$(dirname -- "$0")
+
+# don't run a build if grub.efi exists and is newer than the config files
+if [ -e "${basedir}/grub.efi" ] && \
+     [ "${basedir}/grub.efi" -nt "${basedir}/grub.cfg" ] && \
+     [ "${basedir}/grub.efi" -nt "${basedir}/grub.sh" ]; then
+    remove_efi=0
+    echo "preserving existing grub.efi" >&2
+    exit 0
+fi
+
+##
+# different distributions have different names for grub-mkimage, so
+# search all the known ones
+##
+mkimage=
+for b in grub2-mkimage grub-mkimage; do
+    if which "$b" > /dev/null 2>&1; then
+        mkimage="$b"
+        break
+    fi
+done
+if [ -z "$mkimage" ]; then
+    echo "Can't find grub mkimage" >&2
+    exit 1
+fi
+
+# GRUB's rescue parser doesn't understand 'if'.
+echo 'normal (memdisk)/grub.cfg' > "${basedir}/grub-bootstrap.cfg"
+
+# Now build a memdisk with the correct grub.cfg
+rm -f -- "${basedir}/disk.fat"
+mkfs.msdos -C -- "${basedir}/disk.fat" 64
+mcopy -i "${basedir}/disk.fat" -- "${basedir}/grub.cfg" ::grub.cfg
+
+
+${mkimage} -O x86_64-efi \
+           -p '(crypto0)' \
+           -c "${basedir}/grub-bootstrap.cfg" \
+           -m "${basedir}/disk.fat" \
+           -o "${basedir}/grub.efi" \
+           ${GRUB_MODULES}
+
+remove_efi=0
+echo "grub.efi generated in ${basedir}"