[PATCH v2 1/3] tools: add configure option for disabling pygrub

[Juergen Gross <jgross@xxxxxxxx>]

Add a "--disable-pygrub" option for being able to disable the build
and installation of pygrub.

There are two main reasons to do so:

- A main reason to use pygrub is to allow a PV guest to choose its
  bitness (32- or 64-bit). Pygrub allows that by looking into the boot
  image and to start the guest in the correct mode depending on the
  kernel selected. With 32-bit PV guests being deprecated and the
  possibility to even build a hypervisor without 32-bit PV support,
  this use case is gone for at least some configurations.

- Pygrub is running in dom0 with root privileges. As it is operating
  on guest controlled data (the boot image) and taking decisions based
  on this data, there is a higher security risk. Not being possible
  to use pygrub is thus a step towards a reduction of attack surface.

Default is still to build and install pygrub.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- better wording regarding security aspects (Andrew Cooper)
- add HAVE_PYGRUB to tools/config.h
---
 config/Tools.mk.in |  1 +
 tools/Makefile     |  2 +-
 tools/config.h.in  |  3 +++
 tools/configure    | 34 ++++++++++++++++++++++++++++++++++
 tools/configure.ac |  5 +++++
 5 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/config/Tools.mk.in b/config/Tools.mk.in
index b7cc2961d8..432d7496f1 100644
--- a/config/Tools.mk.in
+++ b/config/Tools.mk.in
@@ -48,6 +48,7 @@ CONFIG_QEMU_XEN     := @qemu_xen@
 CONFIG_QEMUU_EXTRA_ARGS:= @EXTRA_QEMUU_CONFIGURE_ARGS@
 CONFIG_LIBNL        := @libnl@
 CONFIG_GOLANG       := @golang@
+CONFIG_PYGRUB       := @pygrub@
 
 CONFIG_SYSTEMD      := @systemd@
 SYSTEMD_CFLAGS      := @SYSTEMD_CFLAGS@
diff --git a/tools/Makefile b/tools/Makefile
index 1ff90ddfa0..bbd75ebc1a 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -36,7 +36,7 @@ SUBDIRS-$(CONFIG_X86) += debugger
 SUBDIRS-$(CONFIG_TESTS) += tests
 
 SUBDIRS-y += python
-SUBDIRS-y += pygrub
+SUBDIRS-$(CONFIG_PYGRUB) += pygrub
 SUBDIRS-$(OCAML_TOOLS) += ocaml
 
 ifeq ($(CONFIG_RUMP),y)
diff --git a/tools/config.h.in b/tools/config.h.in
index 3071cb3998..eacf1438d8 100644
--- a/tools/config.h.in
+++ b/tools/config.h.in
@@ -45,6 +45,9 @@
 /* ROMBIOS enabled */
 #undef HAVE_ROMBIOS
 
+/* pygrub enabled */
+#undef HAVE_PYGRUB
+
 /* Define to 1 if you have the <stdint.h> header file. */
 #undef HAVE_STDINT_H
 
diff --git a/tools/configure b/tools/configure
index 52b4717d01..44ec7a6477 100755
--- a/tools/configure
+++ b/tools/configure
@@ -707,6 +707,7 @@ AS86
 ipxe
 qemu_traditional
 LINUX_BACKEND_MODULES
+pygrub
 golang
 seabios
 ovmf
@@ -811,6 +812,7 @@ enable_xsmpolicy
 enable_ovmf
 enable_seabios
 enable_golang
+enable_pygrub
 with_linux_backend_modules
 enable_qemu_traditional
 enable_ipxe
@@ -1498,6 +1500,7 @@ Optional Features:
   --enable-ovmf           Enable OVMF (default is DISABLED)
   --disable-seabios       Disable SeaBIOS (default is ENABLED)
   --disable-golang        Disable Go tools (default is ENABLED)
+  --disable-pygrub        Disable pygrub (default is ENABLED)
   --enable-qemu-traditional
                           Enable qemu traditional device model, (DEFAULT is
                           off)
@@ -4287,6 +4290,29 @@ golang=$ax_cv_golang
 
 
 
+# Check whether --enable-pygrub was given.
+if test "${enable_pygrub+set}" = set; then :
+  enableval=$enable_pygrub;
+fi
+
+
+if test "x$enable_pygrub" = "xno"; then :
+
+    ax_cv_pygrub="n"
+
+elif test "x$enable_pygrub" = "xyes"; then :
+
+    ax_cv_pygrub="y"
+
+elif test -z $ax_cv_pygrub; then :
+
+    ax_cv_pygrub="y"
+
+fi
+pygrub=$ax_cv_pygrub
+
+
+
 
 # Check whether --with-linux-backend-modules was given.
 if test "${with_linux_backend_modules+set}" = set; then :
@@ -4595,6 +4621,14 @@ else
 fi
 
 
+if test "x$pygrub" = "xy"; then :
+
+
+$as_echo "#define HAVE_PYGRUB 1" >>confdefs.h
+
+
+fi
+
 
 # Check whether --with-system-qemu was given.
 if test "${with_system_qemu+set}" = set; then :
diff --git a/tools/configure.ac b/tools/configure.ac
index 3cccf41960..0d1c8f9fa3 100644
--- a/tools/configure.ac
+++ b/tools/configure.ac
@@ -89,6 +89,7 @@ AX_ARG_DEFAULT_ENABLE([xsmpolicy], [Disable XSM policy 
compilation])
 AX_ARG_DEFAULT_DISABLE([ovmf], [Enable OVMF])
 AX_ARG_DEFAULT_ENABLE([seabios], [Disable SeaBIOS])
 AX_ARG_DEFAULT_ENABLE([golang], [Disable Go tools])
+AX_ARG_DEFAULT_ENABLE([pygrub], [Disable pygrub])
 
 AC_ARG_WITH([linux-backend-modules],
     AS_HELP_STRING([--with-linux-backend-modules="mod1 mod2"],
@@ -184,6 +185,10 @@ AS_IF([test "x$enable_rombios" = "xyes"], [
 ])
 AC_SUBST(rombios)
 
+AS_IF([test "x$pygrub" = "xy"], [
+    AC_DEFINE([HAVE_PYGRUB], [1], [pygrub enabled])
+])
+
 AC_ARG_WITH([system-qemu],
     AS_HELP_STRING([--with-system-qemu@<:@=PATH@:>@],
        [Use system supplied qemu PATH or qemu (taken from $PATH) as qemu-xen
-- 
2.35.3