From 6ee52814672e95bf1649d45362a6fc5df78a0f52 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Thu, 3 Jun 2021 11:27:34 +0000
Subject: [PATCH] uvm(9): Enable swap encryption by default.

For machines where the performance impact of swapping before the
system has an opportunity to process `vm.swap_encrypt=0' in
/etc/sysctl.conf, you can disable it again by adding

options 	VMSWAP_DEFAULT_PLAINTEXT

to the kernel config.
---
 share/man/man4/options.4 | 10 ++++++++++
 sys/uvm/files.uvm        |  1 +
 sys/uvm/uvm_swap.c       |  5 +++++
 3 files changed, 16 insertions(+)

diff --git a/share/man/man4/options.4 b/share/man/man4/options.4
index e0940df6cecf..f969bb7b3940 100644
--- a/share/man/man4/options.4
+++ b/share/man/man4/options.4
@@ -2203,6 +2203,16 @@ for details.
 .It Cd options VMSWAP
 Enable paging device/file support.
 This option is on by default.
+.It Cd options VMSWAP_DEFAULT_PLAINTEXT
+Store swap in plaintext, not encrypted, which may expose secrets if the
+underlying nonvolatile medium is disclosed.
+This option is off by default; it is available only for extremely slow
+machines where the performance impact of swapping early at boot
+outweighs the security risks.
+Swap encryption can still be turned on dynamically with the
+.Em vm.swap_encrypt
+.Xr sysctl 7
+knob.
 .It Cd options PDPOLICY_CLOCKPRO
 Use CLOCK-Pro, an alternative page replace policy.
 .El
diff --git a/sys/uvm/files.uvm b/sys/uvm/files.uvm
index 223c661e433b..baef1567038c 100644
--- a/sys/uvm/files.uvm
+++ b/sys/uvm/files.uvm
@@ -8,6 +8,7 @@ defflag opt_uvmhist.h		UVMHIST_PRINT: KERNHIST_PRINT
 defparam opt_uvmhist.h		UVMHIST_MAPHIST_SIZE UVMHIST_PDHIST_SIZE
 defflag opt_uvm.h		UVMMAP_COUNTERS
 defparam opt_uvm.h		UVM_RESERVED_PAGES_PER_CPU
+defflag opt_vmswap.h		VMSWAP_DEFAULT_PLAINTEXT
 defflag opt_vmswap.h		VMSWAP : aes
 defflag opt_readahead.h		READAHEAD_STATS
 defflag opt_ubc.h		UBC_STATS
diff --git a/sys/uvm/uvm_swap.c b/sys/uvm/uvm_swap.c
index 1602bbd27d89..dfc23f19d745 100644
--- a/sys/uvm/uvm_swap.c
+++ b/sys/uvm/uvm_swap.c
@@ -35,6 +35,7 @@ __KERNEL_RCSID(0, "$NetBSD: uvm_swap.c,v 1.204 2021/05/23 00:36:36 mrg Exp $");
 #include "opt_uvmhist.h"
 #include "opt_compat_netbsd.h"
 #include "opt_ddb.h"
+#include "opt_vmswap.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -210,7 +211,11 @@ static struct workqueue *sw_reg_workqueue;
 
 /* tuneables */
 u_int uvm_swapisfull_factor = 99;
+#if VMSWAP_DEFAULT_PLAINTEXT
 bool uvm_swap_encrypt = false;
+#else
+bool uvm_swap_encrypt = true;
+#endif
 
 /*
  * prototypes