[PATCH RFC] Add a lockdown_hibernate parameter

[Kelvie Wong]

This allows the user to tell the kernel that they know better (namely,
they secured their swap properly), and that it can enable hibernation.

I've been using this for about a year now, as it doesn't seem like
proper secure hibernation was going to be implemented back then, and
it's now been a year since I've been building my own kernels with this
patch, so getting this upstreamed would save some CO2 from me building
my own kernels every upgrade.

Some other not-me users have also tested the patch:

https://community.frame.work/t/guide-fedora-36-hibernation-with-enabled-secure-boot-and-full-disk-encryption-fde-decrypting-over-tpm2/25474/17

Signed-off-by: Kelvie Wong <kelvie@xxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt |  5 +++++
 kernel/power/hibernate.c                        | 10 +++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 426fa892d311..54785faba9e0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2804,6 +2804,11 @@
 			to extract confidential information from the kernel
 			are also disabled.
 
+	lockdown_hibernate	[HIBERNATION]
+			Enable hibernation even if lockdown is enabled. Enable this only if
+			your swap is encrypted and secured properly, as an attacker can
+			modify the kernel offline during hibernation.
+
 	locktorture.nreaders_stress= [KNL]
 			Set the number of locking read-acquisition kthreads.
 			Defaults to being automatically set based on the
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 89c71fce225d..2221c531d54c 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -36,6 +36,7 @@
 #include "power.h"
 
 
+static int lockdown_hibernate;
 static int nocompress;
 static int noresume;
 static int nohibernate;
@@ -82,7 +83,7 @@ void hibernate_release(void)
 bool hibernation_available(void)
 {
 	return nohibernate == 0 &&
-		!security_locked_down(LOCKDOWN_HIBERNATION) &&
+		(lockdown_hibernate || !security_locked_down(LOCKDOWN_HIBERNATION)) &&
 		!secretmem_active() && !cxl_mem_active();
 }
 
@@ -1340,6 +1341,12 @@ static int __init nohibernate_setup(char *str)
 	return 1;
 }
 
+static int __init lockdown_hibernate_setup(char *str)
+{
+	lockdown_hibernate = 1;
+	return 1;
+}
+
 __setup("noresume", noresume_setup);
 __setup("resume_offset=", resume_offset_setup);
 __setup("resume=", resume_setup);
@@ -1347,3 +1354,4 @@ __setup("hibernate=", hibernate_setup);
 __setup("resumewait", resumewait_setup);
 __setup("resumedelay=", resumedelay_setup);
 __setup("nohibernate", nohibernate_setup);
+__setup("lockdown_hibernate", lockdown_hibernate_setup);
-- 
2.37.3