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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 +431,11 @@
&la57, 0,
"5-level paging for host is enabled");
+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 the 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 a 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 neither of the 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
@@ -68,6 +68,8 @@
{ "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" },
+ { "la57", NT_FREEBSD_FCTL_LA57,
+ "amd64: Allow user VA to use 57bit" },
};
static struct option long_opts[] = {

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