diff --git a/lib/libc/gen/Symbol.map b/lib/libc/gen/Symbol.map
--- a/lib/libc/gen/Symbol.map
+++ b/lib/libc/gen/Symbol.map
@@ -456,6 +456,8 @@
 	aio_read2;
 	aio_write2;
 	execvpe;
+	rtld_get_effective_env_var;
+	rtld_set_effective_env_var;
 };
 
 FBSDprivate_1.0 {
diff --git a/lib/libc/gen/dlfcn.c b/lib/libc/gen/dlfcn.c
--- a/lib/libc/gen/dlfcn.c
+++ b/lib/libc/gen/dlfcn.c
@@ -35,6 +35,7 @@
 #include <sys/mman.h>
 #include <machine/atomic.h>
 #include <dlfcn.h>
+#include <errno.h>
 #include <link.h>
 #include <stddef.h>
 #include <string.h>
@@ -337,4 +338,20 @@
 	return (0);
 }
 
+#pragma weak rtld_get_effective_env_var
+const char *
+rtld_get_effective_env_var(const char *name __unused)
+{
+	_rtld_error(sorry);
+	return (NULL);
+}
+
+#pragma weak rtld_set_effective_env_var
+int
+rtld_set_effective_env_var(const char *name __unused, const char *val __unused)
+{
+	_rtld_error(sorry);
+	return (EINVAL);
+}
+
 #endif /* !defined(IN_LIBDL) || defined(PIC) */
diff --git a/lib/libdl/Symbol.map b/lib/libdl/Symbol.map
--- a/lib/libdl/Symbol.map
+++ b/lib/libdl/Symbol.map
@@ -17,3 +17,8 @@
 FBSD_1.3 {
 	fdlopen;
 };
+
+FBSD_1.8 {
+	rtld_get_effective_env_var;
+	rtld_set_effective_env_var;
+};
diff --git a/libexec/rtld-elf/Symbol.map b/libexec/rtld-elf/Symbol.map
--- a/libexec/rtld-elf/Symbol.map
+++ b/libexec/rtld-elf/Symbol.map
@@ -21,6 +21,11 @@
     fdlopen;
 };
 
+FBSD_1.8 {
+    rtld_get_effective_env_var;
+    rtld_set_effective_env_var;
+};
+
 FBSDprivate_1.0 {
     _rtld_thread_init;
     _rtld_allocate_tls;
diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
--- a/libexec/rtld-elf/rtld.c
+++ b/libexec/rtld-elf/rtld.c
@@ -257,6 +257,8 @@
 int _rtld_get_stack_prot(void) __exported;
 int _rtld_is_dlopened(void *) __exported;
 void _rtld_error(const char *, ...) __exported;
+const char *rtld_get_effective_env_var(const char *name) __exported;
+int rtld_set_effective_env_var(const char *name, const char *val) __exported;
 
 /* Only here to fix -Wmissing-prototypes warnings */
 int __getosreldate(void);
@@ -347,35 +349,42 @@
 	const char * const n;
 	const char *val;
 	const bool unsecure;
+	const bool can_update;
+	bool owned;
 };
-#define LD_ENV_DESC(var, unsec) \
-    [LD_##var] = { .n = #var, .unsecure = unsec }
+#define LD_ENV_DESC(var, unsec, cu)		\
+	[LD_##var] = {				\
+	    .n = #var,				\
+	    .unsecure = unsec,			\
+	    .can_update = cu,			\
+	    .owned = false,			\
+	}
 
 static struct ld_env_var_desc ld_env_vars[] = {
-	LD_ENV_DESC(BIND_NOW, false),
-	LD_ENV_DESC(PRELOAD, true),
-	LD_ENV_DESC(LIBMAP, true),
-	LD_ENV_DESC(LIBRARY_PATH, true),
-	LD_ENV_DESC(LIBRARY_PATH_FDS, true),
-	LD_ENV_DESC(LIBMAP_DISABLE, true),
-	LD_ENV_DESC(BIND_NOT, true),
-	LD_ENV_DESC(DEBUG, true),
-	LD_ENV_DESC(ELF_HINTS_PATH, true),
-	LD_ENV_DESC(LOADFLTR, true),
-	LD_ENV_DESC(LIBRARY_PATH_RPATH, true),
-	LD_ENV_DESC(PRELOAD_FDS, true),
-	LD_ENV_DESC(DYNAMIC_WEAK, true),
-	LD_ENV_DESC(TRACE_LOADED_OBJECTS, false),
-	LD_ENV_DESC(UTRACE, false),
-	LD_ENV_DESC(DUMP_REL_PRE, false),
-	LD_ENV_DESC(DUMP_REL_POST, false),
-	LD_ENV_DESC(TRACE_LOADED_OBJECTS_PROGNAME, false),
-	LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT1, false),
-	LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT2, false),
-	LD_ENV_DESC(TRACE_LOADED_OBJECTS_ALL, false),
-	LD_ENV_DESC(SHOW_AUXV, false),
-	LD_ENV_DESC(STATIC_TLS_EXTRA, false),
-	LD_ENV_DESC(NO_DL_ITERATE_PHDR_AFTER_FORK, false),
+	LD_ENV_DESC(BIND_NOW, false, false),
+	LD_ENV_DESC(PRELOAD, true, false),
+	LD_ENV_DESC(LIBMAP, true, false),
+	LD_ENV_DESC(LIBRARY_PATH, true, true),
+	LD_ENV_DESC(LIBRARY_PATH_FDS, true, true),
+	LD_ENV_DESC(LIBMAP_DISABLE, true, false),
+	LD_ENV_DESC(BIND_NOT, true, false),
+	LD_ENV_DESC(DEBUG, true, true),
+	LD_ENV_DESC(ELF_HINTS_PATH, true, false),
+	LD_ENV_DESC(LOADFLTR, true, false),
+	LD_ENV_DESC(LIBRARY_PATH_RPATH, true, true),
+	LD_ENV_DESC(PRELOAD_FDS, true, false),
+	LD_ENV_DESC(DYNAMIC_WEAK, true, true),
+	LD_ENV_DESC(TRACE_LOADED_OBJECTS, false, false),
+	LD_ENV_DESC(UTRACE, false, true),
+	LD_ENV_DESC(DUMP_REL_PRE, false, true),
+	LD_ENV_DESC(DUMP_REL_POST, false, true),
+	LD_ENV_DESC(TRACE_LOADED_OBJECTS_PROGNAME, false, false),
+	LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT1, false, false),
+	LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT2, false, false),
+	LD_ENV_DESC(TRACE_LOADED_OBJECTS_ALL, false, false),
+	LD_ENV_DESC(SHOW_AUXV, false, false),
+	LD_ENV_DESC(STATIC_TLS_EXTRA, false, false),
+	LD_ENV_DESC(NO_DL_ITERATE_PHDR_AFTER_FORK, false, false),
 };
 
 const char *
@@ -6326,6 +6335,41 @@
 	}
 }
 
+const char *
+rtld_get_effective_env_var(const char *name)
+{
+	const struct ld_env_var_desc *lvd;
+	u_int i;
+
+	for (i = 0; i < nitems(ld_env_vars); i++) {
+		lvd = &ld_env_vars[i];
+		if (strcmp(lvd->n, name) == 0)
+			return (lvd->val);
+	}
+	return (NULL);
+}
+
+int
+rtld_set_effective_env_var(const char *name, const char *val)
+{
+	struct ld_env_var_desc *lvd;
+	u_int i;
+
+	for (i = 0; i < nitems(ld_env_vars); i++) {
+		lvd = &ld_env_vars[i];
+		if (strcmp(lvd->n, name) != 0)
+			continue;
+		if (!lvd->can_update || (lvd->unsecure && !trust))
+			return (EPERM);
+		if (lvd->owned)
+			free(__DECONST(char *, lvd->val));
+		lvd->val = xstrdup(val);
+		lvd->owned = true;
+		return (0);
+	}
+	return (ENOENT);
+}
+
 /*
  * Overrides for libc_pic-provided functions.
  */
diff --git a/sys/sys/link_elf.h b/sys/sys/link_elf.h
--- a/sys/sys/link_elf.h
+++ b/sys/sys/link_elf.h
@@ -93,10 +93,12 @@
 __BEGIN_DECLS
 
 typedef int (*__dl_iterate_hdr_callback)(struct dl_phdr_info *, size_t, void *);
-extern int dl_iterate_phdr(__dl_iterate_hdr_callback, void *);
+int dl_iterate_phdr(__dl_iterate_hdr_callback, void *);
 int _rtld_addr_phdr(const void *, struct dl_phdr_info *);
 int _rtld_get_stack_prot(void);
 int _rtld_is_dlopened(void *);
+const char *rtld_get_effective_env_var(const char *name);
+int rtld_set_effective_env_var(const char *name, const char *val);
 
 #ifdef __ARM_EABI__
 void * dl_unwind_find_exidx(const void *, int *);