3 files changed, 94 insertions, 9 deletions

diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index ead487e80510..bd08616ed8ba 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -33,3 +33,4 @@ proc-$(CONFIG_PROC_KCORE)	+= kcore.o
 proc-$(CONFIG_PROC_VMCORE)	+= vmcore.o
 proc-$(CONFIG_PRINTK)	+= kmsg.o
 proc-$(CONFIG_PROC_PAGE_MONITOR)	+= page.o
+proc-$(CONFIG_BOOT_CONFIG)	+= bootconfig.o
diff --git a/fs/proc/bootconfig.c b/fs/proc/bootconfig.c
new file mode 100644
index 000000000000..9955d75c0585
--- /dev/null
+++ b/fs/proc/bootconfig.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * /proc/bootconfig - Extra boot configuration
+ */
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/printk.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/bootconfig.h>
+#include <linux/slab.h>
+
+static char *saved_boot_config;
+
+static int boot_config_proc_show(struct seq_file *m, void *v)
+{
+	if (saved_boot_config)
+		seq_puts(m, saved_boot_config);
+	return 0;
+}
+
+/* Rest size of buffer */
+#define rest(dst, end) ((end) > (dst) ? (end) - (dst) : 0)
+
+/* Return the needed total length if @size is 0 */
+static int __init copy_xbc_key_value_list(char *dst, size_t size)
+{
+	struct xbc_node *leaf, *vnode;
+	const char *val;
+	char *key, *end = dst + size;
+	int ret = 0;
+
+	key = kzalloc(XBC_KEYLEN_MAX, GFP_KERNEL);
+
+	xbc_for_each_key_value(leaf, val) {
+		ret = xbc_node_compose_key(leaf, key, XBC_KEYLEN_MAX);
+		if (ret < 0)
+			break;
+		ret = snprintf(dst, rest(dst, end), "%s = ", key);
+		if (ret < 0)
+			break;
+		dst += ret;
+		vnode = xbc_node_get_child(leaf);
+		if (vnode && xbc_node_is_array(vnode)) {
+			xbc_array_for_each_value(vnode, val) {
+				ret = snprintf(dst, rest(dst, end), "\"%s\"%s",
+					val, vnode->next ? ", " : "\n");
+				if (ret < 0)
+					goto out;
+				dst += ret;
+			}
+		} else {
+			ret = snprintf(dst, rest(dst, end), "\"%s\"\n", val);
+			if (ret < 0)
+				break;
+			dst += ret;
+		}
+	}
+out:
+	kfree(key);
+
+	return ret < 0 ? ret : dst - (end - size);
+}
+
+static int __init proc_boot_config_init(void)
+{
+	int len;
+
+	len = copy_xbc_key_value_list(NULL, 0);
+	if (len < 0)
+		return len;
+
+	if (len > 0) {
+		saved_boot_config = kzalloc(len + 1, GFP_KERNEL);
+		if (!saved_boot_config)
+			return -ENOMEM;
+
+		len = copy_xbc_key_value_list(saved_boot_config, len + 1);
+		if (len < 0) {
+			kfree(saved_boot_config);
+			return len;
+		}
+	}
+
+	proc_create_single("bootconfig", 0, NULL, boot_config_proc_show);
+
+	return 0;
+}
+fs_initcall(proc_boot_config_init);
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 72c07a34cff0..608233dfd29c 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -41,24 +41,19 @@ enum proc_param {
 	Opt_hidepid,
 };
 
-static const struct fs_parameter_spec proc_param_specs[] = {
+static const struct fs_parameter_spec proc_fs_parameters[] = {
 	fsparam_u32("gid",	Opt_gid),
 	fsparam_u32("hidepid",	Opt_hidepid),
 	{}
 };
 
-static const struct fs_parameter_description proc_fs_parameters = {
-	.name		= "proc",
-	.specs		= proc_param_specs,
-};
-
 static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
 	struct proc_fs_context *ctx = fc->fs_private;
 	struct fs_parse_result result;
 	int opt;
 
-	opt = fs_parse(fc, &proc_fs_parameters, param, &result);
+	opt = fs_parse(fc, proc_fs_parameters, param, &result);
 	if (opt < 0)
 		return opt;
 
@@ -71,7 +66,7 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		ctx->hidepid = result.uint_32;
 		if (ctx->hidepid < HIDEPID_OFF ||
 		    ctx->hidepid > HIDEPID_INVISIBLE)
-			return invalf(fc, "proc: hidepid value must be between 0 and 2.\n");
+			return invalfc(fc, "hidepid value must be between 0 and 2.\n");
 		break;
 
 	default:
@@ -207,7 +202,7 @@ static void proc_kill_sb(struct super_block *sb)
 static struct file_system_type proc_fs_type = {
 	.name			= "proc",
 	.init_fs_context	= proc_init_fs_context,
-	.parameters		= &proc_fs_parameters,
+	.parameters		= proc_fs_parameters,
 	.kill_sb		= proc_kill_sb,
 	.fs_flags		= FS_USERNS_MOUNT | FS_DISALLOW_NOTIFY_PERM,
 };