diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c
--- a/sys/amd64/amd64/elf_machdep.c
+++ b/sys/amd64/amd64/elf_machdep.c
@@ -170,11 +170,13 @@
 {
 	if ((imgp->proc->p_md.md_flags & P_MD_LA57) != 0)
 		return (true);
+	if (fctl0 != NULL && (*fctl0 & NT_FREEBSD_FCTL_LA57) != 0)
+		return (true);
 	if (fctl0 == NULL || (*fctl0 & NT_FREEBSD_FCTL_LA48) != 0)
 		return (false);
 	if ((imgp->proc->p_md.md_flags & P_MD_LA48) != 0)
 		return (false);
-	return (true);
+	return (!prefer_uva_la48);
 }
 
 static Elf64_Brandinfo freebsd_brand_info_la48 = {
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -431,6 +431,15 @@
     &la57, 0,
     "5-level paging for host is enabled");
 
+/*
+ * The default value is needed in order to preserve compatibility with
+ * some userspace programs that put tags into sign-extended bits.
+ */
+int prefer_uva_la48 = 1;
+SYSCTL_INT(_vm_pmap, OID_AUTO, prefer_uva_la48, CTLFLAG_RDTUN,
+    &prefer_uva_la48, 0,
+    "Userspace maps are limited to LA48 unless otherwise configured");
+
 static bool
 pmap_is_la57(pmap_t pmap)
 {
diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h
--- a/sys/amd64/include/md_var.h
+++ b/sys/amd64/include/md_var.h
@@ -51,6 +51,7 @@
 extern vm_paddr_t intel_graphics_stolen_size;
 
 extern int la57;
+extern int prefer_uva_la48;
 
 extern vm_paddr_t kernphys;
 extern vm_paddr_t KERNend;
diff --git a/sys/sys/elf_common.h b/sys/sys/elf_common.h
--- a/sys/sys/elf_common.h
+++ b/sys/sys/elf_common.h
@@ -824,6 +824,7 @@
 #define	NT_FREEBSD_FCTL_WXNEEDED	0x00000008
 #define	NT_FREEBSD_FCTL_LA48		0x00000010
 /* was ASG_DISABLE, do not reuse	0x00000020 */
+#define	NT_FREEBSD_FCTL_LA57		0x00000040
 
 /* Values for n_type.  Used in core files. */
 #define	NT_PRSTATUS	1	/* Process status. */
diff --git a/usr.bin/elfctl/elfctl.1 b/usr.bin/elfctl/elfctl.1
--- a/usr.bin/elfctl/elfctl.1
+++ b/usr.bin/elfctl/elfctl.1
@@ -95,6 +95,20 @@
 .Bd -literal -offset indent
 elfctl -e =0x5 file
 .Ed
+.Sh NOTES
+On amd64, on a machine with LA57 (5-level paging) mode supported and
+enabled, if both
+.Va la57
+and
+.Va la48
+feature flags are specified, the
+.Va la57
+feature has priority over
+.Va la48 .
+The
+.Va vm.pmap.prefer_uva_la48
+sysctl MIB defines the default user address space size for binaries
+which do not set either of these flags.
 .Sh SEE ALSO
 .Xr mitigations 7
 .Sh HISTORY
diff --git a/usr.bin/elfctl/elfctl.c b/usr.bin/elfctl/elfctl.c
--- a/usr.bin/elfctl/elfctl.c
+++ b/usr.bin/elfctl/elfctl.c
@@ -67,7 +67,10 @@
 	    "Disable implicit PROT_MAX" },
 	{ "nostackgap",	NT_FREEBSD_FCTL_STKGAP_DISABLE, "Disable stack gap" },
 	{ "wxneeded",	NT_FREEBSD_FCTL_WXNEEDED, "Requires W+X mappings" },
-	{ "la48",	NT_FREEBSD_FCTL_LA48, "amd64: Limit user VA to 48bit" },
+	{ "la48",	NT_FREEBSD_FCTL_LA48,
+	    "amd64: Limit user virtual addresses to 48bits" },
+	{ "la57",	NT_FREEBSD_FCTL_LA57,
+	    "amd64: Allow the use of 57-bit virtual addresses when available" },
 };
 
 static struct option long_opts[] = {