Libguestfs - Dec 2022 - [v2v PATCH 2/2] convert_windows: fix up the UEFI fallback boot loader if broken

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2149629

The second patch is the interesting one; the first patch is just a
trivial refactoring.

Laszlo Ersek (2):
  convert_linux.get_uefi_arch_suffix: move to Utils
  convert_windows: fix up the UEFI fallback boot loader if broken

 lib/utils.mli              |  5 ++++
 convert/convert_linux.ml   |  6 -----
 convert/convert_windows.ml | 25 ++++++++++++++++++++
 lib/utils.ml               |  5 ++++
 4 files changed, 35 insertions(+), 6 deletions(-)

So that Windows conversion can use the same function.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2149629
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 lib/utils.mli            | 5 +++++
 convert/convert_linux.ml | 6 ------
 lib/utils.ml             | 5 +++++
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/lib/utils.mli b/lib/utils.mli
index d431e21f5ce9..5687bf75867e 100644
--- a/lib/utils.mli
+++ b/lib/utils.mli
@@ -98,3 +98,8 @@ val get_disk_allocated : dir:string -> disknr:int ->
int64 option
     image, according to the "base:allocation" metadata context. If
the context
     is not supported by the NBD server behind the socket, the function returns
     None. *)
+
+val get_uefi_arch_suffix : string -> string option
+(** [get_uefi_arch_suffix arch] maps [arch] from [inspect.i_arch]
representation
+    to UEFI spec representation.  If a mapping cannot be found, [None] is
+    returned. *)
diff --git a/convert/convert_linux.ml b/convert/convert_linux.ml
index 5bfdac5aa6d9..cde3b037542f 100644
--- a/convert/convert_linux.ml
+++ b/convert/convert_linux.ml
@@ -1327,12 +1327,6 @@ let convert (g : G.guestfs) source inspect
keep_serial_console _          info (f_"Can't fix UEFI bootloader. VM
may not boot.")
       in
 
-      let get_uefi_arch_suffix = function
-        | "x86_64" -> Some "X64"
-        | "i386" -> Some "X32"
-        | _ -> None
-      in
-
       match get_uefi_arch_suffix inspect.i_arch with
       | None -> cant_fix_uefi ()
       | Some suffix -> (
diff --git a/lib/utils.ml b/lib/utils.ml
index fd45769415c7..26e7e259001b 100644
--- a/lib/utils.ml
+++ b/lib/utils.ml
@@ -258,3 +258,8 @@ let get_disk_allocated ~dir ~disknr             Some
!allocated
          ) else None
        )
+
+let get_uefi_arch_suffix = function
+  | "x86_64" -> Some "X64"
+  | "i386" -> Some "X32"
+  | _ -> None

The "fallback" (or "default") boot behavior is described at
great length
here:

https://blog.uncooperative.org/uefi/linux/shim/efi%20system%20partition/2014/02/06/the-efi-system-partition.html

The gist of it applies to all UEFI OSes, including Windows. For the
fallback boot behavior to work, the \EFI\BOOT\BOOTX64.efi boot loader on
the EFI system partition must match the installed operating system. We've
encountered a physical machine, during a virt-p2v conversion, where (a)
\EFI\BOOT\BOOTX64.efi belongs to a previously installed, but now wiped,
RHEL (hence shim+grub) deployment, and (b) the currently installed
operating system is Windows.

Virt-v2v never transfers the UEFI variables (including the UEFI boot
options) of the source, therefore the converted VM always relies on the
default boot behavior when it is first started up. In the above scenario,
where \EFI\BOOT\BOOTX64.efi is actually "shim", the mismatch is
triggered
at first boot after conversion, and a broken grub shell is reached instead
of the Windows boot loader.

Detect this situation by investigating \EFI\BOOT\BOOTX64.efi on the EFI
system partition of a Windows disk image. If the file is missing, or is
not -- as expected -- a duplicate of \EFI\Microsoft\Boot\bootmgfw.efi,
then copy the latter to the former.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2149629
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---

Notes:
    Tested with a freshly installed Win2019 guest whose
    \EFI\BOOT\BOOTX64.efi binary I manually corrupted.

 convert/convert_windows.ml | 25 ++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/convert/convert_windows.ml b/convert/convert_windows.ml
index 34a5044dd338..57a7ff03398f 100644
--- a/convert/convert_windows.ml
+++ b/convert/convert_windows.ml
@@ -836,17 +836,42 @@ let convert (g : G.guestfs) _ inspect _ static_ips        
);
       with
         Not_found -> ()
+
+    and fix_win_uefi_fallback esp_path uefi_arch +      (* [esp_path] is on
NTFS, and therefore it is considered case-sensitive;
+       * refer to
+       *
<https://libguestfs.org/guestfs.3.html#guestfs_case_sensitive_path>.
+       * However, the EFI system partition mounted under [esp_path] is FAT32
per
+       * UEFI spec, and the Linux vfat driver in the libguestfs appliance
treats
+       * pathnames case-insensitively. Therefore, we're free to use any
case in
+       * the ESP-relative pathnames below.
+       *)
+      let bootmgfw = sprintf "%s/efi/microsoft/boot/bootmgfw.efi"
esp_path in
+      if g#is_file bootmgfw then
+        let bootdir = sprintf "%s/efi/boot" esp_path in
+        let fallback = sprintf "%s/boot%s.efi" bootdir uefi_arch in
+        if not (g#is_file fallback) || not (g#equal fallback bootmgfw) then (
+          info (f_"Fixing UEFI bootloader.");
+          g#rm_rf bootdir;
+          g#mkdir_p bootdir;
+          g#cp_a bootmgfw fallback
+        )
     in
 
     match inspect.i_firmware with
     | I_BIOS -> ()
     | I_UEFI esp_list ->
       let esp_temp_path = g#mkdtemp "/Windows/Temp/ESP_XXXXXX" in
+      let uefi_arch = get_uefi_arch_suffix inspect.i_arch in
 
       List.iter (
         fun dev_path ->
         g#mount dev_path esp_temp_path;
         fix_win_uefi_bcd esp_temp_path;
+        (match uefi_arch with
+         | Some uefi_arch -> fix_win_uefi_fallback esp_temp_path uefi_arch
+         | None -> ()
+        );
         g#umount esp_temp_path;
       ) esp_list;