diff --git a/lib/libjail/jail.h b/lib/libjail/jail.h
--- a/lib/libjail/jail.h
+++ b/lib/libjail/jail.h
@@ -33,6 +33,7 @@
 #define	JP_BOOL		0x02
 #define	JP_NOBOOL	0x04
 #define	JP_JAILSYS	0x08
+#define	JP_KEYVALUE	0x10
 
 #define JAIL_ERRMSGLEN	1024
 
diff --git a/lib/libjail/jail.c b/lib/libjail/jail.c
--- a/lib/libjail/jail.c
+++ b/lib/libjail/jail.c
@@ -59,6 +59,7 @@
 static int kldload_param(const char *name);
 static char *noname(const char *name);
 static char *nononame(const char *name);
+static char *kvname(const char *name);
 
 char jail_errmsg[JAIL_ERRMSGLEN];
 
@@ -907,22 +908,41 @@
 		 * the "no" counterpart to a boolean.
 		 */
 		nname = nononame(name);
-		if (nname == NULL) {
-		unknown_parameter:
-			snprintf(jail_errmsg, JAIL_ERRMSGLEN,
-			    "unknown parameter: %s", jp->jp_name);
-			errno = ENOENT;
-			return (-1);
+		if (nname != NULL) {
+			snprintf(desc.s, sizeof(desc.s), SJPARAM ".%s", nname);
+			miblen = sizeof(mib) - 2 * sizeof(int);
+			if (sysctl(mib, 2, mib + 2, &miblen, desc.s,
+			    strlen(desc.s)) >= 0) {
+				name = alloca(strlen(nname) + 1);
+				strcpy(name, nname);
+				free(nname);
+				jp->jp_flags |= JP_NOBOOL;
+				goto mib_desc;
+			}
+			free(nname);
 		}
-		name = alloca(strlen(nname) + 1);
-		strcpy(name, nname);
-		free(nname);
-		snprintf(desc.s, sizeof(desc.s), SJPARAM ".%s", name);
-		miblen = sizeof(mib) - 2 * sizeof(int);
-		if (sysctl(mib, 2, mib + 2, &miblen, desc.s,
-		    strlen(desc.s)) < 0)
-			goto unknown_parameter;
-		jp->jp_flags |= JP_NOBOOL;
+		/*
+		 * It might be an assumed sub-node of a fmt='A,keyvalue' sysctl.
+		 */
+		nname = kvname(name);
+		if (nname != NULL) {
+			snprintf(desc.s, sizeof(desc.s), SJPARAM ".%s", nname);
+			miblen = sizeof(mib) - 2 * sizeof(int);
+			if (sysctl(mib, 2, mib + 2, &miblen, desc.s,
+			    strlen(desc.s)) >= 0) {
+				name = alloca(strlen(nname) + 1);
+				strcpy(name, nname);
+				free(nname);
+				jp->jp_flags |= JP_KEYVALUE;
+				goto mib_desc;
+			}
+			free(nname);
+		}
+unknown_parameter:
+		snprintf(jail_errmsg, JAIL_ERRMSGLEN,
+		    "unknown parameter: %s", jp->jp_name);
+		errno = ENOENT;
+		return (-1);
 	}
  mib_desc:
 	mib[1] = 4;
@@ -943,6 +963,12 @@
 		else if ((desc.i & CTLTYPE) != CTLTYPE_NODE)
 			goto unknown_parameter;
 	}
+	/* Make sure it is a valid keyvalue param */
+	if (jp->jp_flags & JP_KEYVALUE) {
+		if ((desc.i & CTLTYPE) != CTLTYPE_STRING ||
+		    strcmp(desc.s, "A,keyvalue") != 0)
+			goto unknown_parameter;
+	}
 	/* See if this is an array type. */
 	p = strchr(desc.s, '\0');
 	isarray  = 0;
@@ -1119,3 +1145,26 @@
 		strcpy(nname, name + 2);
 	return (nname);
 }
+
+static char *
+kvname(const char *name)
+{
+	const char *p;
+	char *kvname;
+	size_t len;
+
+	p = strchr(name, '.');
+	if (p == NULL)
+		return (NULL);
+
+	len = p - name;
+	kvname = malloc(len + 1);
+	if (kvname == NULL) {
+		strerror_r(errno, jail_errmsg, JAIL_ERRMSGLEN);
+		return (NULL);
+	}
+	strncpy(kvname, name, len);
+	kvname[len] = '\0';
+
+	return (kvname);
+}
diff --git a/sys/conf/files b/sys/conf/files
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -3805,6 +3805,7 @@
 kern/kern_idle.c		standard
 kern/kern_intr.c		standard
 kern/kern_jail.c		standard
+kern/kern_jailmeta.c		standard
 kern/kern_kcov.c		optional kcov			\
 	compile-with "${NOSAN_C} ${MSAN_CFLAGS}"
 kern/kern_khelp.c		standard
diff --git a/sys/kern/kern_jail.c b/sys/kern/kern_jail.c
--- a/sys/kern/kern_jail.c
+++ b/sys/kern/kern_jail.c
@@ -4254,7 +4254,7 @@
 /*
  * Jail-related sysctls.
  */
-static SYSCTL_NODE(_security, OID_AUTO, jail, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
+SYSCTL_NODE(_security, OID_AUTO, jail, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
     "Jails");
 
 #if defined(INET) || defined(INET6)
diff --git a/sys/kern/kern_jailmeta.c b/sys/kern/kern_jailmeta.c
new file mode 100644
--- /dev/null
+++ b/sys/kern/kern_jailmeta.c
@@ -0,0 +1,706 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2024 SkunkWerks GmbH
+ *
+ * This software was developed by Igor Ostapenko <igoro@FreeBSD.org>
+ * under sponsorship from SkunkWerks GmbH.
+ */
+
+#include <sys/param.h>
+#include <sys/_bitset.h>
+#include <sys/bitset.h>
+#include <sys/lock.h>
+#include <sys/sx.h>
+#include <sys/kernel.h>
+#include <sys/mount.h>
+#include <sys/malloc.h>
+#include <sys/jail.h>
+#include <sys/osd.h>
+#include <sys/proc.h>
+
+/*
+ * Buffer limit
+ *
+ * The hard limit is the actual value used during setting or modification. The
+ * soft limit is used solely by the security.jail.param.meta and .env sysctl. If
+ * the hard limit is decreased, the soft limit may remain higher to ensure that
+ * previously set meta strings can still be correctly interpreted by end-user
+ * interfaces, such as jls(8).
+ */
+
+static uint32_t jm_maxbufsize_hard = 4096;
+static uint32_t jm_maxbufsize_soft = 4096;
+
+static int
+jm_sysctl_meta_maxbufsize(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	uint32_t newmax = 0;
+
+	/* only reading */
+
+	if (req->newptr == NULL) {
+		sx_slock(&allprison_lock);
+		error = SYSCTL_OUT(req, &jm_maxbufsize_hard,
+		    sizeof(jm_maxbufsize_hard));
+		sx_sunlock(&allprison_lock);
+
+		return (error);
+	}
+
+	/* reading and writing */
+
+	sx_xlock(&allprison_lock);
+
+	error = SYSCTL_OUT(req, &jm_maxbufsize_hard,
+	    sizeof(jm_maxbufsize_hard));
+	if (error != 0)
+		goto end;
+
+	error = SYSCTL_IN(req, &newmax, sizeof(newmax));
+	if (error != 0)
+		goto end;
+
+	jm_maxbufsize_hard = newmax;
+	if (jm_maxbufsize_hard >= jm_maxbufsize_soft)
+		jm_maxbufsize_soft = jm_maxbufsize_hard;
+	else if (TAILQ_EMPTY(&allprison))
+		/*
+		 * For now, this is the simplest way to
+		 * avoid O(n) iteration over all prisons in
+		 * case of a large n.
+		 */
+		jm_maxbufsize_soft = jm_maxbufsize_hard;
+
+end:
+	sx_xunlock(&allprison_lock);
+	return (error);
+}
+SYSCTL_PROC(_security_jail, OID_AUTO, meta_maxbufsize,
+    CTLTYPE_U32 | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
+    jm_sysctl_meta_maxbufsize, "IU",
+    "Maximum buffer size of each meta and env");
+
+
+/* Allowed chars */
+
+#define NCHARS	256
+BITSET_DEFINE(charbitset, NCHARS);
+static struct charbitset allowedchars;
+
+static int
+jm_sysctl_meta_allowedchars(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+	unsigned char chars[NCHARS];
+	int len = 0;
+	const bool readonly = req->newptr == NULL;
+
+	readonly ? sx_slock(&allprison_lock) : sx_xlock(&allprison_lock);
+
+	if (!BIT_ISFULLSET(NCHARS, &allowedchars))
+		for (size_t i = 1; i < NCHARS; i++) {
+			if (!BIT_ISSET(NCHARS, i, &allowedchars))
+				continue;
+			chars[len] = i;
+			len++;
+		}
+	chars[len] = 0;
+
+	error = sysctl_handle_string(oidp, chars, arg2, req);
+
+	if (!readonly && error == 0) {
+		if (chars[0] == 0) {
+			BIT_FILL(NCHARS, &allowedchars);
+		} else {
+			BIT_ZERO(NCHARS, &allowedchars);
+			for (size_t i = 0; i < NCHARS; i++) {
+				if (chars[i] == 0)
+					break;
+				BIT_SET(NCHARS, chars[i], &allowedchars);
+			}
+		}
+	}
+
+	readonly ? sx_sunlock(&allprison_lock) : sx_xunlock(&allprison_lock);
+
+	return (error);
+}
+SYSCTL_PROC(_security_jail, OID_AUTO, meta_allowedchars,
+    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, NCHARS,
+    jm_sysctl_meta_allowedchars, "A",
+    "The single-byte chars allowed to be used for meta and env"
+    " (empty string means all chars are allowed)");
+
+
+/* Jail parameter announcement */
+
+static int
+jm_sysctl_param_meta(SYSCTL_HANDLER_ARGS)
+{
+	uint32_t soft;
+
+	sx_slock(&allprison_lock);
+	soft = jm_maxbufsize_soft;
+	sx_sunlock(&allprison_lock);
+
+	return (sysctl_jail_param(oidp, arg1, soft, req));
+}
+SYSCTL_PROC(_security_jail_param, OID_AUTO, meta,
+    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
+    jm_sysctl_param_meta, "A,keyvalue",
+    "Jail meta information hidden from the jail");
+SYSCTL_PROC(_security_jail_param, OID_AUTO, env,
+    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE, NULL, 0,
+    jm_sysctl_param_meta, "A,keyvalue",
+    "Jail meta information readable by the jail");
+
+
+/* OSD -- generic logic for any metadata buffer */
+
+struct meta {
+	char *name;
+	u_int osd_slot;
+	osd_method_t methods[PR_MAXMETHOD];
+};
+
+/*
+ * A chain of hunks depicts the final buffer after all manipulations.
+ */
+struct hunk {
+	char *p;
+	size_t len;  /* may include \0 char or not */
+	char *owned; /* must be freed */
+	struct hunk *next;
+};
+
+static inline struct hunk *
+jm_h_alloc(void)
+{
+	/* all fields are zeroed */
+	return (malloc(sizeof(struct hunk), M_PRISON, M_WAITOK | M_ZERO));
+}
+
+static inline struct hunk *
+jm_h_prepend(struct hunk *h, char *p, size_t len)
+{
+	struct hunk *n;
+
+	n = jm_h_alloc();
+	n->p = p;
+	n->len = len;
+
+	if (h == NULL)
+		return (n);
+
+	n->next = h;
+	return (n);
+}
+
+static inline void
+jm_h_cut_line(struct hunk *h, char *begin)
+{
+	struct hunk *rem;
+	char *end;
+
+	/* Find the end of key=value\n */
+	for (end = begin; (end + 1) - h->p < h->len; end++)
+		if (*end == '\0' || *end == '\n')
+			break;
+
+	/* Pick up non-empty remainder */
+	if ((end + 1) - h->p < h->len && *(end + 1) != '\0') {
+		rem = jm_h_alloc();
+		rem->p = end + 1;
+		rem->len = h->p + h->len - rem->p;
+
+		/* insert */
+		rem->next = h->next;
+		h->next = rem;
+	}
+
+	/* Shorten this hunk */
+	h->len = begin - h->p;
+}
+
+static inline void
+jm_h_cut_occurrences(struct hunk *h, const char *key, size_t keylen)
+{
+	char *p = h->p;
+
+#define nexthunk()					\
+	do {						\
+		h = h->next;				\
+		p = (h == NULL) ? NULL : h->p;		\
+	} while (0)
+
+	while (p != NULL) {
+		p = strnstr(p, key, h->len - (p - h->p));
+		if (p == NULL) {
+			nexthunk();
+			continue;
+		}
+		if ((p == h->p || *(p - 1) == '\n') && p[keylen] == '=') {
+			jm_h_cut_line(h, p);
+			nexthunk();
+			continue;
+		}
+		/* continue with this hunk */
+		p += keylen;
+		/* empty? the next hunk then */
+		if ((p - h->p) >= h->len)
+			nexthunk();
+	}
+}
+
+static inline size_t
+jm_h_len(struct hunk *h)
+{
+	size_t len = 0;
+	while (h != NULL) {
+		len += h->len;
+		h = h->next;
+	}
+	return (len);
+}
+
+static inline void
+jm_h_assemble(char *dst, struct hunk *h)
+{
+	while (h != NULL) {
+		if (h->len > 0) {
+			memcpy(dst, h->p, h->len);
+			dst += h->len;
+			/* if not the last hunk then concatenate with \n */
+			if (h->next != NULL && *(dst - 1) == '\0')
+				*(dst - 1) = '\n';
+		}
+		h = h->next;
+	}
+}
+
+static inline struct hunk *
+jm_h_freechain(struct hunk *h)
+{
+	struct hunk *n = h;
+	while (n != NULL) {
+		h = n;
+		n = h->next;
+		free(h->owned, M_PRISON);
+		free(h, M_PRISON);
+	}
+
+	return (NULL);
+}
+
+static int
+jm_osd_method_set(void *obj, void *data, const struct meta *meta)
+{
+	struct prison *pr = obj;
+	struct vfsoptlist *opts = data;
+	struct vfsopt *opt;
+
+	char *origosd;
+	char *origosd_copy;
+	char *oldosd;
+	char *osd;
+	size_t osdlen;
+	struct hunk *h;
+	char *key;
+	size_t keylen;
+	int error;
+	int repeats = 0;
+	bool repeat;
+
+	sx_assert(&allprison_lock, SA_XLOCKED);
+
+again:
+	origosd = NULL;
+	origosd_copy = NULL;
+	osd = NULL;
+	h = NULL;
+	error = 0;
+	repeat = false;
+	TAILQ_FOREACH(opt, opts, link) {
+		/* Look for options with <metaname> prefix */
+		if (strstr(opt->name, meta->name) != opt->name)
+			continue;
+		/* Consider only full <metaname> or <metaname>.* ones */
+		if (opt->name[strlen(meta->name)] != '.' &&
+		    opt->name[strlen(meta->name)] != '\0')
+			continue;
+		opt->seen = 1;
+
+		/* The very first preconditions */
+		if (opt->len <= 0)
+			continue;
+		if (opt->len > jm_maxbufsize_hard) {
+			error = EFBIG;
+			break;
+		}
+		/* vfsopt is expected to provide NULL-terminated strings */
+		if (((char *)opt->value)[opt->len - 1] != '\0') {
+			error = EINVAL;
+			break;
+		}
+
+		/* Work with our own copy of existing metadata */
+		if (h == NULL) {
+			h = jm_h_alloc(); /* zeroed */
+			mtx_lock(&pr->pr_mtx);
+			origosd = osd_jail_get(pr, meta->osd_slot);
+			if (origosd != NULL) {
+				origosd_copy = malloc(strlen(origosd) + 1,
+				    M_PRISON, M_NOWAIT);
+				if (origosd_copy == NULL)
+					error = ENOMEM;
+				else {
+					h->p = origosd_copy;
+					h->len = strlen(origosd) + 1;
+					memcpy(h->p, origosd, h->len);
+				}
+			}
+			mtx_unlock(&pr->pr_mtx);
+			if (error != 0)
+				break;
+		}
+
+		/* Change the whole metadata */
+		if (strcmp(opt->name, meta->name) == 0) {
+			if (opt->len > jm_maxbufsize_hard) {
+				error = EFBIG;
+				break;
+			}
+			h = jm_h_freechain(h);
+			h = jm_h_prepend(h, opt->value,
+			    /* avoid empty NULL-terminated string */
+			    (opt->len > 1) ? opt->len : 0);
+			continue;
+		}
+
+		/* Add or replace existing key=value */
+		key = opt->name + strlen(meta->name) + 1;
+		keylen = strlen(key);
+		if (keylen < 1) {
+			error = EINVAL;
+			break;
+		}
+		jm_h_cut_occurrences(h, key, keylen);
+		h = jm_h_prepend(h, NULL, 0);
+		h->len = keylen + 1 + opt->len; /* key=value\0 */
+		h->owned = malloc(h->len, M_PRISON, M_WAITOK | M_ZERO);
+		h->p = h->owned;
+		memcpy(h->p, key, keylen);
+		h->p[keylen] = '=';
+		memcpy(h->p + keylen + 1, opt->value, opt->len);
+	}
+
+	if (h == NULL || error != 0)
+		goto end;
+
+	/* Assemble the contiguous buffer */
+	osdlen = jm_h_len(h);
+	if (osdlen > jm_maxbufsize_hard) {
+		error = EFBIG;
+		goto end;
+	}
+	if (osdlen > 1) {
+		osd = malloc(osdlen, M_PRISON, M_WAITOK);
+		jm_h_assemble(osd, h);
+		osd[osdlen - 1] = '\0'; /* sealed */
+		/* Check allowed chars */
+		for (size_t i = 0; i < osdlen; i++) {
+			if (osd[i] == 0)
+				continue;
+			if (!BIT_ISSET(NCHARS, osd[i], &allowedchars)) {
+				error = EINVAL;
+				goto end;
+			}
+		}
+	}
+
+	/* Compare and swap buffers */
+	mtx_lock(&pr->pr_mtx);
+	oldosd = osd_jail_get(pr, meta->osd_slot);
+	if (oldosd == origosd) {
+		error = osd_jail_set(pr, meta->osd_slot, osd);
+	} else {
+		/* someone else was quicker - re-apply opts then */
+		error = EAGAIN;
+		repeat = true;
+	}
+	mtx_unlock(&pr->pr_mtx);
+	if (error == 0)
+		osd = oldosd;
+
+end:
+	jm_h_freechain(h);
+	free(osd, M_PRISON);
+	free(origosd_copy, M_PRISON);
+
+	if (repeat) {
+		repeats++;
+		if (repeats < 3)
+			goto again;
+	}
+
+	return (error);
+}
+
+static int
+jm_osd_method_get(void *obj, void *data, const struct meta *meta)
+{
+	struct prison *pr = obj;
+	struct vfsoptlist *opts = data;
+	struct vfsopt *opt;
+	char *osd = NULL;
+	char empty = '\0';
+	int error = 0;
+	bool locked = false;
+	const char *key;
+	size_t keylen;
+	const char *p;
+
+	sx_assert(&allprison_lock, SA_SLOCKED);
+
+	TAILQ_FOREACH(opt, opts, link) {
+		if (strstr(opt->name, meta->name) != opt->name)
+			continue;
+		if (opt->name[strlen(meta->name)] != '.' &&
+		    opt->name[strlen(meta->name)] != '\0')
+			continue;
+
+		opt->seen = 1;
+
+		if (!locked) {
+			mtx_lock(&pr->pr_mtx);
+			locked = true;
+			osd = osd_jail_get(pr, meta->osd_slot);
+			if (osd == NULL)
+				osd = &empty;
+		}
+
+		/* Provide full metadata */
+		if (strcmp(opt->name, meta->name) == 0) {
+			if (strlcpy(opt->value, osd, opt->len) >= opt->len) {
+				error = EINVAL;
+				break;
+			}
+			continue;
+		}
+
+		/* Extract a specific key=value\n */
+		p = osd;
+		key = opt->name + strlen(meta->name) + 1;
+		keylen = strlen(key);
+		while ((p = strstr(p, key)) != NULL) {
+			if ((p == osd || *(p - 1) == '\n')
+			    && p[keylen] == '=') {
+				if (strlcpy(opt->value, p + keylen + 1,
+				    MIN(opt->len, strchr(p + keylen + 1, '\n') -
+				    (p + keylen + 1) + 1)) >= opt->len) {
+					error = EINVAL;
+					break;
+				}
+			}
+			p += keylen;
+		}
+	}
+
+	if (locked)
+		mtx_unlock(&pr->pr_mtx);
+
+	return (error);
+}
+
+static int
+jm_osd_method_check(void *obj __unused, void *data, const struct meta *meta)
+{
+	struct vfsoptlist *opts = data;
+	struct vfsopt *opt;
+
+	TAILQ_FOREACH(opt, opts, link) {
+		if (strstr(opt->name, meta->name) != opt->name)
+			continue;
+		if (opt->name[strlen(meta->name)] != '.' &&
+		    opt->name[strlen(meta->name)] != '\0')
+			continue;
+		opt->seen = 1;
+	}
+
+	return (0);
+}
+
+static void
+jm_osd_destructor(void *osd)
+{
+	free(osd, M_PRISON);
+}
+
+
+/* OSD -- meta */
+
+static struct meta meta;
+
+static inline int
+jm_osd_method_set_meta(void *obj, void *data)
+{
+	return (jm_osd_method_set(obj, data, &meta));
+}
+
+static inline int
+jm_osd_method_get_meta(void *obj, void *data)
+{
+	return (jm_osd_method_get(obj, data, &meta));
+}
+
+static inline int
+jm_osd_method_check_meta(void *obj, void *data)
+{
+	return (jm_osd_method_check(obj, data, &meta));
+}
+
+static struct meta meta = {
+	.name = "meta",
+	.osd_slot = 0,
+	.methods = {
+		[PR_METHOD_SET] =	jm_osd_method_set_meta,
+		[PR_METHOD_GET] =	jm_osd_method_get_meta,
+		[PR_METHOD_CHECK] =	jm_osd_method_check_meta,
+	}
+};
+
+
+/* OSD -- env */
+
+static struct meta env;
+
+static inline int
+jm_osd_method_set_env(void *obj, void *data)
+{
+	return (jm_osd_method_set(obj, data, &env));
+}
+
+static inline int
+jm_osd_method_get_env(void *obj, void *data)
+{
+	return (jm_osd_method_get(obj, data, &env));
+}
+
+static inline int
+jm_osd_method_check_env(void *obj, void *data)
+{
+	return (jm_osd_method_check(obj, data, &env));
+}
+
+static struct meta env = {
+	.name = "env",
+	.osd_slot = 0,
+	.methods = {
+		[PR_METHOD_SET] =	jm_osd_method_set_env,
+		[PR_METHOD_GET] =	jm_osd_method_get_env,
+		[PR_METHOD_CHECK] =	jm_osd_method_check_env,
+	}
+};
+
+
+/* A jail can read its 'env' */
+
+static int
+jm_sysctl_env(SYSCTL_HANDLER_ARGS)
+{
+	struct prison *pr;
+	char empty = '\0';
+	char *tmpbuf;
+	size_t outlen;
+	int error = 0;
+
+	pr = req->td->td_ucred->cr_prison;
+
+	mtx_lock(&pr->pr_mtx);
+	arg1 = osd_jail_get(pr, env.osd_slot);
+	if (arg1 == NULL) {
+		tmpbuf = &empty;
+		outlen = 1;
+	} else {
+		outlen = strlen(arg1) + 1;
+		if (req->oldptr != NULL) {
+			tmpbuf = malloc(outlen, M_PRISON, M_NOWAIT);
+			error = (tmpbuf == NULL) ? ENOMEM : 0;
+			if (error == 0)
+				memcpy(tmpbuf, arg1, outlen);
+		}
+	}
+	mtx_unlock(&pr->pr_mtx);
+
+	if (error != 0)
+		return (error);
+
+	if (req->oldptr == NULL)
+		SYSCTL_OUT(req, NULL, outlen);
+	else {
+		SYSCTL_OUT(req, tmpbuf, outlen);
+		if (tmpbuf != &empty)
+			free(tmpbuf, M_PRISON);
+	}
+
+	return (error);
+}
+SYSCTL_PROC(_security_jail, OID_AUTO, env,
+    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
+    0, 0, jm_sysctl_env, "A", "Meta information provided by parent jail");
+
+
+/* Setup and tear down */
+
+static int
+jm_sysinit(void *arg __unused)
+{
+	/* Default set of allowed chars */
+
+	BIT_ZERO(NCHARS, &allowedchars);
+
+	/* Base64 */
+	for (size_t i = 0x41; i <= 0x5A; i++)	/* A-Z */
+		BIT_SET(NCHARS, i, &allowedchars);
+	for (size_t i = 0x61; i <= 0x7A; i++)	/* a-z */
+		BIT_SET(NCHARS, i, &allowedchars);
+	for (size_t i = 0x30; i <= 0x39; i++)	/* 0-9 */
+		BIT_SET(NCHARS, i, &allowedchars);
+	BIT_SET(NCHARS, 0x2B, &allowedchars);	/* + */
+	BIT_SET(NCHARS, 0x2F, &allowedchars);	/* / */
+	BIT_SET(NCHARS, 0x3D, &allowedchars);	/* = */
+
+	/* key=value\n format */
+	BIT_SET(NCHARS, 0x0A, &allowedchars);	/* LF */
+	BIT_SET(NCHARS, 0x0D, &allowedchars);	/* CR */
+
+	/* Extra */
+	BIT_SET(NCHARS, 0x09, &allowedchars);	/* HT */
+	BIT_SET(NCHARS, 0x20, &allowedchars);	/* SP */
+	BIT_SET(NCHARS, 0x2C, &allowedchars);	/* , */
+	BIT_SET(NCHARS, 0x2D, &allowedchars);	/* - */
+	BIT_SET(NCHARS, 0x2E, &allowedchars);	/* . */
+	BIT_SET(NCHARS, 0x3A, &allowedchars);	/* : */
+	BIT_SET(NCHARS, 0x40, &allowedchars);	/* @ */
+	BIT_SET(NCHARS, 0x5F, &allowedchars);	/* _ */
+
+
+	meta.osd_slot = osd_jail_register(jm_osd_destructor, meta.methods);
+	env.osd_slot = osd_jail_register(jm_osd_destructor, env.methods);
+
+	return (0);
+}
+
+static int
+jm_sysuninit(void *arg __unused)
+{
+	osd_jail_deregister(meta.osd_slot);
+	osd_jail_deregister(env.osd_slot);
+
+	return (0);
+}
+
+SYSINIT(jailmeta, SI_SUB_DRIVERS, SI_ORDER_ANY, jm_sysinit, NULL);
+SYSUNINIT(jailmeta, SI_SUB_DRIVERS, SI_ORDER_ANY, jm_sysuninit, NULL);
diff --git a/sys/sys/jail.h b/sys/sys/jail.h
--- a/sys/sys/jail.h
+++ b/sys/sys/jail.h
@@ -376,6 +376,7 @@
 /*
  * Sysctls to describe jail parameters.
  */
+SYSCTL_DECL(_security_jail);
 SYSCTL_DECL(_security_jail_param);
 
 #define SYSCTL_JAIL_PARAM_DECL(name)					\
diff --git a/tests/sys/kern/Makefile b/tests/sys/kern/Makefile
--- a/tests/sys/kern/Makefile
+++ b/tests/sys/kern/Makefile
@@ -59,6 +59,8 @@
 
 ATF_TESTS_SH+=	coredump_phnum_test
 ATF_TESTS_SH+=	logsigexit_test
+ATF_TESTS_SH+=	jailmeta
+TEST_METADATA.jailmeta+=	is_exclusive="true"
 ATF_TESTS_SH+=	sonewconn_overflow
 TEST_METADATA.sonewconn_overflow+=	required_programs="python"
 TEST_METADATA.sonewconn_overflow+=	required_user="root"
diff --git a/tests/sys/kern/jailmeta.sh b/tests/sys/kern/jailmeta.sh
new file mode 100644
--- /dev/null
+++ b/tests/sys/kern/jailmeta.sh
@@ -0,0 +1,631 @@
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (c) 2024 SkunkWerks GmbH
+#
+# This software was developed by Igor Ostapenko <igoro@FreeBSD.org>
+# under sponsorship from SkunkWerks GmbH.
+#
+
+setup()
+{
+	# Check if we have enough buffer space for testing
+	if [ $(sysctl -n security.jail.meta_maxbufsize) -lt 128 ]; then
+		atf_skip "sysctl security.jail.meta_maxbufsize must be 128+ for testing."
+	fi
+
+	# Check if chars required for testing are allowed
+	allowed="$(sysctl -b security.jail.meta_allowedchars | hexdump -e '1/1 "%02x\n"')"
+	# ABCabctv =0-9\t\n
+	for b in 41 42 43 61 62 63 74 76 20 30 31 32 33 34 35 36 37 38 39 09 0a
+	do
+		if ! echo $allowed | grep -q $b; then
+			atf_skip "sysctl security.jail.meta_allowedchars is not wide enough for testing"
+		fi
+	done
+}
+
+atf_test_case "jail_create" "cleanup"
+jail_create_head()
+{
+	atf_set descr 'Test that metadata can be set upon jail creation with jail(8)'
+	atf_set require.user root
+	atf_set execenv jail
+}
+jail_create_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta="a b c" env="C B A"
+
+	atf_check -s exit:0 -o inline:"a b c\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"C B A\n" \
+	    jls -jj env
+}
+jail_create_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "jail_modify" "cleanup"
+jail_modify_head()
+{
+	atf_set descr 'Test that metadata can be modified after jail creation with jail(8)'
+	atf_set require.user root
+	atf_set execenv jail
+}
+jail_modify_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta="a	b	c" env="CAB"
+
+	atf_check -s exit:0 -o inline:"a	b	c\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"CAB\n" \
+	    jls -jj env
+
+	atf_check -s exit:0 \
+	    jail -m name=j meta="t1=A t2=B" env="CAB2"
+
+	atf_check -s exit:0 -o inline:"t1=A t2=B\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"CAB2\n" \
+	    jls -jj env
+}
+jail_modify_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "jail_add" "cleanup"
+jail_add_head()
+{
+	atf_set descr 'Test that metadata can be added to an existing jail with jail(8)'
+	atf_set require.user root
+	atf_set execenv jail
+}
+jail_add_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist host.hostname=jail1
+
+	atf_check -s exit:0 -o inline:'""\n' \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:'""\n' \
+	    jls -jj env
+
+	atf_check -s exit:0 \
+	    jail -m name=j meta="$(jot 3 1 3)" env="$(jot 2 11 12)"
+
+	atf_check -s exit:0 -o inline:"1\n2\n3\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"11\n12\n" \
+	    jls -jj env
+}
+jail_add_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "jail_reset" "cleanup"
+jail_reset_head()
+{
+	atf_set descr 'Test that metadata can be reset to an empty string with jail(8)'
+	atf_set require.user root
+	atf_set execenv jail
+}
+jail_reset_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta="123" env="456"
+
+	atf_check -s exit:0 -o inline:"123\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"456\n" \
+	    jls -jj env
+
+	atf_check -s exit:0 \
+	    jail -m name=j meta= env=
+
+	atf_check -s exit:0 -o inline:'""\n' \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:'""\n' \
+	    jls -jj env
+}
+jail_reset_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "jls_libxo" "cleanup"
+jls_libxo_head()
+{
+	atf_set descr 'Test that metadata can be read with jls(8) using libxo'
+	atf_set require.user root
+	atf_set execenv jail
+}
+jls_libxo_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta="a b c" env="1 2 3"
+
+	atf_check -s exit:0 -o inline:'{"__version": "2", "jail-information": {"jail": [{"name":"j","meta":"a b c"}]}}\n' \
+	    jls -jj --libxo json name meta
+	atf_check -s exit:0 -o inline:'{"__version": "2", "jail-information": {"jail": [{"env":"1 2 3"}]}}\n' \
+	    jls -jj --libxo json env
+}
+jls_libxo_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "flua_create" "cleanup"
+flua_create_head()
+{
+	atf_set descr 'Test that metadata can be set upon jail creation with flua'
+	atf_set require.user root
+	atf_set execenv jail
+}
+flua_create_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    /usr/libexec/flua -ljail -e 'jail.setparams("j", {["meta"]="t1 t2=v2", ["env"]="BAC", ["persist"]="true"}, jail.CREATE)'
+
+	atf_check -s exit:0 -o inline:"t1 t2=v2\n" \
+	    /usr/libexec/flua -ljail -e 'jid, res = jail.getparams("j", {"meta"}); print(res["meta"])'
+	atf_check -s exit:0 -o inline:"BAC\n" \
+	    /usr/libexec/flua -ljail -e 'jid, res = jail.getparams("j", {"env"}); print(res["env"])'
+}
+flua_create_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "flua_modify" "cleanup"
+flua_modify_head()
+{
+	atf_set descr 'Test that metadata can be changed with flua after jail creation'
+	atf_set require.user root
+	atf_set execenv jail
+}
+flua_modify_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta="ABC" env="123"
+
+	atf_check -s exit:0 -o inline:"ABC\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"123\n" \
+	    jls -jj env
+
+	atf_check -s exit:0 \
+	    /usr/libexec/flua -ljail -e 'jail.setparams("j", {["meta"]="t1 t2=v", ["env"]="4"}, jail.UPDATE)'
+
+	atf_check -s exit:0 -o inline:"t1 t2=v\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"4\n" \
+	    jls -jj env
+}
+flua_modify_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "env_readable_by_jail" "cleanup"
+env_readable_by_jail_head()
+{
+	atf_set descr 'Test that a jail can read its own env parameter via sysctl(8)'
+	atf_set require.user root
+	atf_set execenv jail
+}
+env_readable_by_jail_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -jj
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta="a b c" env="CBA"
+
+	atf_check -s exit:0 -o inline:"a b c\n" \
+	    jls -jj meta
+	atf_check -s exit:0 -o inline:"CBA\n" \
+	    jls -jj env
+
+	atf_check -s exit:0 -o inline:"CBA\n" \
+	    jexec j sysctl -n security.jail.env
+}
+env_readable_by_jail_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "not_inheritable" "cleanup"
+not_inheritable_head()
+{
+	atf_set descr 'Test that a jail does not inherit metadata from its parent jail'
+	atf_set require.user root
+	atf_set execenv jail
+}
+not_inheritable_body()
+{
+	setup
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -j parent
+
+	atf_check -s exit:0 \
+	    jail -c name=parent children.max=1 persist meta="abc" env="cba"
+
+	jexec parent jail -c name=child persist
+
+	atf_check -s exit:0 -o inline:"abc\n" \
+	    jls -j parent meta
+	atf_check -s exit:0 -o inline:'""\n' \
+	    jls -j parent.child meta
+
+	atf_check -s exit:0 -o inline:"cba\n" \
+	    jexec parent sysctl -n security.jail.env
+	atf_check -s exit:0 -o inline:"\n" \
+	    jexec parent.child sysctl -n security.jail.env
+}
+not_inheritable_cleanup()
+{
+	jail -r parent.child
+	jail -r parent
+	return 0
+}
+
+atf_test_case "maxbufsize" "cleanup"
+maxbufsize_head()
+{
+	atf_set descr 'Test that metadata buffer maximum size can be changed'
+	atf_set require.user root
+}
+maxbufsize_body()
+{
+	setup
+
+	jn=jailmeta_maxbufsize
+
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -j $jn
+
+	# the size counts string length and the trailing \0 char
+	origmax=$(sysctl -n security.jail.meta_maxbufsize)
+
+	# must be fine with current max
+	atf_check -s exit:0 \
+	    jail -c name=$jn persist meta="$(printf %$((origmax-1))s)"
+	atf_check -s exit:0 -o inline:"${origmax}\n" \
+	    jls -j $jn meta | wc -c
+	#
+	atf_check -s exit:0 \
+	    jail -m name=$jn env="$(printf %$((origmax-1))s)"
+	atf_check -s exit:0 -o inline:"${origmax}\n" \
+	    jls -j $jn env | wc -c
+
+	# should not allow exceeding current max
+	atf_check -s not-exit:0 -e match:"too large" \
+	    jail -m name=$jn meta="$(printf %${origmax}s)"
+	#
+	atf_check -s not-exit:0 -e match:"too large" \
+	    jail -m name=$jn env="$(printf %${origmax}s)"
+
+	# should allow the same size with increased max
+	newmax=$((origmax + 1))
+	sysctl security.jail.meta_maxbufsize=$newmax
+	atf_check -s exit:0 \
+	    jail -m name=$jn meta="$(printf %${origmax}s)"
+	atf_check -s exit:0 -o inline:"${origmax}\n" \
+	    jls -j $jn meta | wc -c
+	#
+	atf_check -s exit:0 \
+	    jail -m name=$jn env="$(printf %${origmax}s)"
+	atf_check -s exit:0 -o inline:"${origmax}\n" \
+	    jls -j $jn env | wc -c
+
+	# decrease back to the original max
+	sysctl security.jail.meta_maxbufsize=$origmax
+	atf_check -s not-exit:0 -e match:"too large" \
+	    jail -m name=$jn meta="$(printf %${origmax}s)"
+	#
+	atf_check -s not-exit:0 -e match:"too large" \
+	    jail -m name=$jn env="$(printf %${origmax}s)"
+
+	# the previously set long meta is still readable as is
+	# due to the soft limit remains higher than the hard limit
+	atf_check_equal '${newmax}' '$(sysctl -n security.jail.param.meta)'
+	atf_check_equal '${newmax}' '$(sysctl -n security.jail.param.env)'
+	atf_check -s exit:0 -o inline:"${origmax}\n" \
+	    jls -j $jn meta | wc -c
+	#
+	atf_check -s exit:0 -o inline:"${origmax}\n" \
+	    jls -j $jn env | wc -c
+}
+maxbufsize_cleanup()
+{
+	jail -r jailmeta_maxbufsize
+	return 0
+}
+
+atf_test_case "allowedchars" "cleanup"
+allowedchars_head()
+{
+	atf_set descr 'Test that the set of allowed chars can be changed'
+	atf_set require.user root
+}
+allowedchars_body()
+{
+	setup
+
+	jn=jailmeta_allowedchars
+	atf_check -s not-exit:0 -e match:"not found" -o ignore \
+	    jls -j $jn
+	atf_check -s exit:0 \
+	    jail -c name=$jn persist
+
+	# Save the original value
+	sysctl -b security.jail.meta_allowedchars > meta_allowedchars.bin
+
+	# All chars
+	sysctl security.jail.meta_allowedchars=
+	printf $(jot -w '\%o' -s '' -n 127 1 127) > 7bit.bin
+	atf_check -s exit:0 \
+	    jail -m name=$jn meta="$(cat 7bit.bin)" env="$(cat 7bit.bin)"
+	jls -j $jn meta > meta.bin
+	jls -j $jn env > env.bin
+	printf '\n' >> 7bit.bin # jls adds a newline
+	atf_check -s exit:0 diff 7bit.bin meta.bin
+	atf_check -s exit:0 diff 7bit.bin env.bin
+
+	# Limited set
+	sysctl security.jail.meta_allowedchars="$(printf 'AB\1\2_\3\11C')"
+	# should be okay if within the limits
+	atf_check -s exit:0 \
+	    jail -m name=$jn meta="$(printf 'C\11A\3')" env="$(printf '\1A\2B\3')"
+	# should error and not change env
+	atf_check -s not-exit:0 -o ignore -e ignore \
+	    jail -m name=$jn meta="$(printf 'XC\11A\3')" env="$(printf '_\1A\2B\3')"
+	# should error and not change meta
+	atf_check -s not-exit:0 -o ignore -e ignore \
+	    jail -m name=$jn meta="$(printf '_C\11A\3')" env="$(printf '\1A\2B\3x')"
+	# should stay intact after errors
+	atf_check -s exit:0 -o inline:"43094103" \
+	    jls -j $jn meta | hexdump -e '1/1 "%02x"'
+	atf_check -s exit:0 -o inline:"0141024303" \
+	    jls -j $jn env | hexdump -e '1/1 "%02x"'
+
+}
+allowedchars_cleanup()
+{
+	# Restore the original value
+	test -f meta_allowedchars.bin \
+	    && sysctl security.jail.meta_allowedchars="'$(cat meta_allowedchars.bin)'"
+	rm *.bin
+
+	jail -r jailmeta_allowedchars
+	return 0
+}
+
+atf_test_case "keyvalue" "cleanup"
+keyvalue_head()
+{
+	atf_set descr 'Test that metadata can be handled as a set of key=value\n strings using jail(8) and jls(8)'
+	atf_set require.user root
+	atf_set execenv jail
+}
+keyvalue_generic()
+{
+	local meta=$1
+
+	atf_check -sexit:0 -oinline:'""\n'	jls -jj $meta
+
+	# Should be able to extract a key added manually
+	atf_check -sexit:0				jail -m name=j $meta="a=1"
+	atf_check -sexit:0 -oinline:'a=1\n'		jls -jj $meta
+	atf_check -sexit:0 -oinline:'1\n'		jls -jj $meta.a
+	atf_check -sexit:0				jail -m name=j $meta="$(printf 'a=2\nb=3')"
+	atf_check -sexit:0 -oinline:'a=2\nb=3\n'	jls -jj $meta
+	atf_check -sexit:0 -oinline:'2\n'		jls -jj $meta.a
+	atf_check -sexit:0 -oinline:'3\n'		jls -jj $meta.b
+
+	# Should provide an empty string for a non-found key
+	atf_check -sexit:0 -oinline:'""\n'		jls -jj $meta.c
+
+	# Should be able to lookup multiple keys at once
+	atf_check -sexit:0 -oinline:'3 2\n'		jls -jj $meta.b $meta.a
+
+	# Should be able to lookup keys and the whole buffer at once
+	atf_check -sexit:0 -oinline:'3 a=2\nb=3 2\n'	jls -jj $meta.b $meta $meta.a
+
+	# Should be able to lookup a key with libxo-based output
+	s='{"__version": "2", "jail-information": {"jail": [{"'$meta'.b":"3","'$meta'.c":""}]}}\n'
+	atf_check -s exit:0 -o inline:"$s"		jls -jj --libxo json $meta.b $meta.c
+
+	# Should be able to lookup a key with flua
+	atf_check -s exit:0 -o inline:"2\n"	\
+	    /usr/libexec/flua -ljail -e 'jid, res = jail.getparams("j", {"'$meta'.a"}); print(res["'$meta'.a"])'
+
+	# Should be fine if a buffer is empty
+	atf_check -sexit:0				jail -m name=j $meta=
+	atf_check -sexit:0 -oinline:'"" "" ""\n'	jls -jj $meta.c $meta $meta.a
+
+	# Should allow adding a new key
+	atf_check -sexit:0				jail -m name=j $meta.a=1
+	atf_check -sexit:0 -oinline:'1\n'		jls -jj $meta.a
+	atf_check -sexit:0 -oinline:'a=1\n'		jls -jj $meta
+
+	# Should allow adding multiple new keys at once
+	atf_check -sexit:0				jail -m name=j $meta.c=3 $meta.b=2
+	atf_check -sexit:0 -oinline:'3\n'		jls -jj $meta.c
+	atf_check -sexit:0 -oinline:'2\n'		jls -jj $meta.b
+	atf_check -sexit:0 -oinline:'b=2\nc=3\na=1\n'	jls -jj $meta
+
+	# Should replace existing keys
+	atf_check -sexit:0				jail -m name=j $meta.a=A $meta.c=C
+	atf_check -sexit:0 -oinline:'A\n'		jls -jj $meta.a
+	atf_check -sexit:0 -oinline:'C\n'		jls -jj $meta.c
+	atf_check -sexit:0 -oinline:'c=C\na=A\nb=2\n'	jls -jj $meta
+
+	# Should treat empty value correctly
+	atf_check -sexit:0				jail -m name=j $meta.b $meta.a=
+	atf_check -sexit:0 -oinline:'""\n'		jls -jj $meta.a
+	atf_check -sexit:0 -oinline:'""\n'		jls -jj $meta.b
+	atf_check -sexit:0 -oinline:'a=\nb=\nc=C\n'	jls -jj $meta
+
+	# Should allow changing the whole buffer and per key at once (order matters)
+	atf_check -sexit:0				jail -m name=j $meta.a=1 $meta=ttt $meta.b=2
+	atf_check -sexit:0 -oinline:'""\n'		jls -jj $meta.a
+	atf_check -sexit:0 -oinline:'2\n'		jls -jj $meta.b
+	atf_check -sexit:0 -oinline:'b=2\nttt\n'	jls -jj $meta
+
+	# Should treat only the first equal sign as syntax
+	atf_check -sexit:0				jail -m name=j $meta.b==
+	atf_check -sexit:0 -oinline:'=\n'		jls -jj $meta.b
+	atf_check -sexit:0 -oinline:'b==\nttt\n'	jls -jj $meta
+
+	# Should allow adding or modifying keys with flua
+	atf_check -s exit:0 \
+	    /usr/libexec/flua -ljail -e 'jail.setparams("j", {["'$meta.b'"]="ttt", ["'$meta'.c"]="C"}, jail.UPDATE)'
+	atf_check -sexit:0 -oinline:'ttt\n'		jls -jj $meta.b
+	atf_check -sexit:0 -oinline:'C\n'		jls -jj $meta.c
+}
+keyvalue_body()
+{
+	setup
+
+	atf_check -s exit:0 \
+	    jail -c name=j persist meta env
+
+	keyvalue_generic "meta"
+	keyvalue_generic "env"
+}
+keyvalue_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_test_case "keyvalue_contention" "cleanup"
+keyvalue_contention_head()
+{
+	atf_set descr 'Try to stress metadata read/write mechanism with some contention'
+	atf_set require.user root
+	atf_set execenv jail
+	atf_set timeout 30
+}
+keyvalue_stresser()
+{
+	local jailname=$1
+	local modifier=$2
+
+	while true
+	do
+		jail -m name=$jailname $modifier
+	done
+}
+keyvalue_contention_body()
+{
+	setup
+
+	atf_check -s exit:0 jail -c name=j persist meta env
+
+	keyvalue_stresser "j" "meta.a=1" &
+	apid=$!
+	keyvalue_stresser "j" "meta.b=2" &
+	bpid=$!
+	keyvalue_stresser "j" "env.c=3" &
+	cpid=$!
+	keyvalue_stresser "j" "env.d=4" &
+	dpid=$!
+
+	for it in $(jot 8)
+	do
+		sleep 1
+		jail -m name=j meta='meta=META' env='env=ENV'
+		atf_check -sexit:0 -oinline:'META\n'	jls -jj meta.meta
+		atf_check -sexit:0 -oinline:'ENV\n'	jls -jj env.env
+		atf_check -sexit:0 -oinline:'1\n'	jls -jj meta.a
+		atf_check -sexit:0 -oinline:'2\n'	jls -jj meta.b
+		atf_check -sexit:0 -oinline:'3\n'	jls -jj env.c
+		atf_check -sexit:0 -oinline:'4\n'	jls -jj env.d
+	done
+
+	# TODO: Think of adding a stresser on the kernel side which does
+	#       osd_set() w/o allprison lock. It could test the compare
+	#       and swap mechanism in jm_osd_method_set().
+
+	kill -9 $apid $bpid $cpid $dpid
+}
+keyvalue_contention_cleanup()
+{
+	jail -r j
+	return 0
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case "jail_create"
+	atf_add_test_case "jail_modify"
+	atf_add_test_case "jail_add"
+	atf_add_test_case "jail_reset"
+
+	atf_add_test_case "jls_libxo"
+
+	atf_add_test_case "flua_create"
+	atf_add_test_case "flua_modify"
+
+	atf_add_test_case "env_readable_by_jail"
+	atf_add_test_case "not_inheritable"
+
+	atf_add_test_case "maxbufsize"
+	atf_add_test_case "allowedchars"
+
+	atf_add_test_case "keyvalue"
+	atf_add_test_case "keyvalue_contention"
+}
diff --git a/usr.sbin/jail/jail.8 b/usr.sbin/jail/jail.8
--- a/usr.sbin/jail/jail.8
+++ b/usr.sbin/jail/jail.8
@@ -513,6 +513,36 @@
 The number for the jail's
 .Va kern.osreldate
 and uname -K.
+.It Va meta , Va env
+An arbitrary string associated with the jail.
+Its maximum buffer size is controlled by the global
+.Va security.jail.meta_maxbufsize
+sysctl, which can only be adjusted by the non-jailed root user.
+While the
+.Va meta
+is hidden from the jail, the
+.Va env
+is readable through the
+.Va security.jail.env
+sysctl.
+The set of allowed single-byte characters for both buffers is limited by the
+global
+.Va security.jail.meta_allowedchars
+sysctl, which is also tunable by the non-jailed root user.
+All characters are allowed if it is set to an empty string.
+.Pp
+Each buffer can be treated as a set of key=value\\n strings.
+In order to add or replace a specific key the
+.Va meta.keyname=value
+or
+.Va env.keyname=value
+parameter notations must be used.
+The
+.Va meta.keyname
+or
+.Va env.keyname
+notations are used for reading.
+Multiple keys can be queried or modified with a single command.
 .It Va allow.*
 Some restrictions of the jail environment may be set on a per-jail
 basis.