linux-kernel - [PATCH 1/2] lockdown: Switch implementation to using bitmap

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Message-ID: <20250321102422.640271-2-nik.borisov@suse.com>
Date: Fri, 21 Mar 2025 12:24:20 +0200
From: Nikolay Borisov <nik.borisov@...e.com>
To: linux-security-module@...r.kernel.org
Cc: paul@...l-moore.com,
	serge@...lyn.com,
	kees@...nel.org,
	linux-kernel@...r.kernel.org,
	kirill.shutemov@...ux.intel.com,
	linux-coco@...ts.linux.dev,
	Nikolay Borisov <nik.borisov@...e.com>
Subject: [PATCH 1/2] lockdown: Switch implementation to using bitmap

Tracking the lockdown at the depth granularity rather than at the
individual is somewhat inflexible as it provides an "all or nothing"
approach. Instead there are use cases where it  will be useful to be
able to lockdown individual features - TDX for example wants to disable
access to just /dev/mem.

To accommodate this use case switch the internal implementation to using
a bitmap so that individual lockdown features can be turned on. At the
same time retain the existing semantic where
INTEGRITY_MAX/CONFIDENTIALITY_MAX are treated as wildcards meaning "lock
everything below me".

Signed-off-by: Nikolay Borisov <nik.borisov@...e.com>
---
 security/lockdown/lockdown.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index cf83afa1d879..5014d18c423f 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -10,12 +10,13 @@
  * 2 of the Licence, or (at your option) any later version.
  */
 
+#include <linux/bitmap.h>
 #include <linux/security.h>
 #include <linux/export.h>
 #include <linux/lsm_hooks.h>
 #include <uapi/linux/lsm.h>
 
-static enum lockdown_reason kernel_locked_down;
+static DECLARE_BITMAP(kernel_locked_down, LOCKDOWN_CONFIDENTIALITY_MAX);
 
 static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
 						 LOCKDOWN_INTEGRITY_MAX,
@@ -26,10 +27,15 @@ static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
  */
 static int lock_kernel_down(const char *where, enum lockdown_reason level)
 {
-	if (kernel_locked_down >= level)
-		return -EPERM;
 
-	kernel_locked_down = level;
+	if (level > LOCKDOWN_CONFIDENTIALITY_MAX)
+		return -EINVAL;
+
+	if (level == LOCKDOWN_INTEGRITY_MAX || level == LOCKDOWN_CONFIDENTIALITY_MAX)
+		bitmap_set(kernel_locked_down, 1, level);
+	else
+		bitmap_set(kernel_locked_down, level, 1);
+
 	pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
 		  where);
 	return 0;
@@ -62,13 +68,12 @@ static int lockdown_is_locked_down(enum lockdown_reason what)
 		 "Invalid lockdown reason"))
 		return -EPERM;
 
-	if (kernel_locked_down >= what) {
+	if (test_bit(what, kernel_locked_down)) {
 		if (lockdown_reasons[what])
 			pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
 				  current->comm, lockdown_reasons[what]);
 		return -EPERM;
 	}
-
 	return 0;
 }
 
@@ -105,7 +110,7 @@ static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 		if (lockdown_reasons[level]) {
 			const char *label = lockdown_reasons[level];
 
-			if (kernel_locked_down == level)
+			if (test_bit(level, kernel_locked_down))
 				offset += sprintf(temp+offset, "[%s] ", label);
 			else
 				offset += sprintf(temp+offset, "%s ", label);
-- 
2.43.0