From 09bb28bdef3fb5e7d08bdd641601ca0c0d4d82b4 Mon Sep 17 00:00:00 2001
From: Julien Grall <jgrall@amazon.com>
Date: Sat, 17 Apr 2021 17:38:28 +0100
Subject: [PATCH 2/2] xen/arm: Boot modules should always be scrubbed if
 bootscrub={on, idle}

The function to initialize the pages (see init_heap_pages()) will request
scrub when the admin request idle bootscrub (default) and state ==
SYS_STATE_active. When bootscrub=on, Xen will scrub any free pages in
heap_init_late().

Currently, the boot modules (e.g. kernels, initramfs) will be discarded/
freed after heap_init_late() is called and system_state switched to
SYS_STATE_active. This means the pages associated with the boot modules
will not get scrubbed before getting re-purposed.

If the memory is assigned to an untrusted domU, it may be able to
retrieve secrets from the modules.

This is part of XSA-372 / CVE-2021-28693.

Fixes: 1774e9b1df27 ("xen/arm: introduce create_domUs")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Stefano Stabellini <sstabellini@kernel.org>
---
 xen/arch/arm/setup.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 441e0e16e9f0..8afb78f2c985 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -72,8 +72,6 @@ domid_t __read_mostly max_init_domid;
 
 static __used void init_done(void)
 {
-    discard_initial_modules();
-
     /* Must be done past setting system_state. */
     unregister_init_virtual_region();
 
@@ -990,6 +988,12 @@ void __init start_xen(unsigned long boot_phys_offset,
     if ( acpi_disabled )
         create_domUs();
 
+    /*
+     * This needs to be called **before** heap_init_late() so modules
+     * will be scrubbed (unless suppressed).
+     */
+    discard_initial_modules();
+
     heap_init_late();
 
     init_trace_bufs();
-- 
2.17.1