[RFC PATCH v1 30/42] security/vbs: run backend probe and HEKI seal at rootfs_initcall

[Sriram Nambakam <snambakam@linux.microsoft.com>]

Move VBS backend probing (vbs_probe_init) from device_initcall and the
HEKI kernel seal (vbs_heki_late_init) from late_initcall to
rootfs_initcall, and link probe.o before core.o so the backend is
registered before the seal runs. At this level the initramfs is
unpacked and the VM planes have been set up (init/ links before
security/), but device drivers, modules and userspace have not started
yet, so the kernel is sealed before anything that could tamper with it
runs.

Signed-off-by: Sriram Nambakam <snambakam@linux.microsoft.com>
---
 security/vbs/Makefile | 5 ++++-
 security/vbs/core.c   | 9 ++++++++-
 security/vbs/probe.c  | 9 +++++----
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/security/vbs/Makefile b/security/vbs/Makefile
index e33052ccde2d..01e831e28ac7 100644
--- a/security/vbs/Makefile
+++ b/security/vbs/Makefile
@@ -1,6 +1,9 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_VBS) += vbs.o
-vbs-y := core.o probe.o
+# probe.o must link before core.o so that, at rootfs_initcall level, the
+# backend is registered (vbs_probe_init) before the HEKI seal runs
+# (vbs_heki_late_init in core.o).
+vbs-y := probe.o core.o
 
 vbs-$(CONFIG_VBS_HEKI)		+= heki.o
 obj-$(CONFIG_VBS_KVM_PLANES)	+= kvm_planes.o
diff --git a/security/vbs/core.c b/security/vbs/core.c
index 16b5329964f9..1167026fc7d1 100644
--- a/security/vbs/core.c
+++ b/security/vbs/core.c
@@ -195,4 +195,11 @@ static int __init vbs_heki_late_init(void)
 
 	return 0;
 }
-late_initcall(vbs_heki_late_init);
+/*
+ * Run at rootfs_initcall level (after vbs_probe_init in probe.o, which links
+ * first) so the kernel is sealed before any device driver, module, or
+ * userspace runs.  The secure plane vcpu already exists by this point because
+ * arch_init_vm_planes() (init/, links before security/) ran earlier in the
+ * same initcall level.
+ */
+rootfs_initcall(vbs_heki_late_init);
diff --git a/security/vbs/probe.c b/security/vbs/probe.c
index 292f3663a996..14aa3d59310b 100644
--- a/security/vbs/probe.c
+++ b/security/vbs/probe.c
@@ -96,8 +96,9 @@ static int __init vbs_probe_init(void)
 }
 
 /*
- * Run at device_initcall level: platform detection (CPUID, MSRs, SMCCC)
- * is complete by this point, but subsystems that consume VBS (module
- * loading, HEKI) have not yet started.
+ * Run at rootfs_initcall level: platform detection (CPUID, MSRs, SMCCC)
+ * is complete by this point, the VM planes have been set up (init/ links
+ * before security/), and subsystems that consume VBS (module loading, HEKI,
+ * device drivers, userspace) have not yet started.
  */
-device_initcall(vbs_probe_init);
+rootfs_initcall(vbs_probe_init);
-- 
2.55.0