linux: Unmap the VDSO page when unloading

linux_shared_page_init() creates an object and grabs and maps a single
page to back the VDSO.  When destroying the VDSO object, we failed to
destroy the mapping and free KVA.  Fix this.

Reviewed by:	kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D28696

(cherry picked from commit 0fc8a79)

sys/amd64/linux/linux_sysvec.c

@@ -818,7 +818,8 @@ static void
 linux_vdso_deinstall(void *param)
 {
 
-	__elfN(linux_shared_page_fini)(linux_shared_page_obj);
+	__elfN(linux_shared_page_fini)(linux_shared_page_obj,
+	    linux_shared_page_mapping);
 }
 SYSUNINIT(elf_linux_vdso_uninit, SI_SUB_EXEC, SI_ORDER_FIRST,
     linux_vdso_deinstall, NULL);

sys/amd64/linux32/linux32_sysvec.c

@@ -961,7 +961,8 @@ static void
 linux_vdso_deinstall(void *param)
 {
 
-	__elfN(linux_shared_page_fini)(linux_shared_page_obj);
+	__elfN(linux_shared_page_fini)(linux_shared_page_obj,
+	    linux_shared_page_mapping);
 }
 SYSUNINIT(elf_linux_vdso_uninit, SI_SUB_EXEC, SI_ORDER_FIRST,
     linux_vdso_deinstall, NULL);

sys/arm64/linux/linux_sysvec.c

@@ -461,7 +461,8 @@ linux_vdso_deinstall(const void *param)
 {
 
 	LIN_SDT_PROBE0(sysvec, linux_vdso_deinstall, todo);
-	__elfN(linux_shared_page_fini)(linux_shared_page_obj);
+	__elfN(linux_shared_page_fini)(linux_shared_page_obj,
+	    linux_shared_page_mapping);
 }
 SYSUNINIT(elf_linux_vdso_uninit, SI_SUB_EXEC, SI_ORDER_FIRST,
     linux_vdso_deinstall, NULL);

sys/compat/linux/linux_vdso.c

@@ -93,9 +93,13 @@ __elfN(linux_shared_page_init)(char **mapping)
 }
 
 void
-__elfN(linux_shared_page_fini)(vm_object_t obj)
+__elfN(linux_shared_page_fini)(vm_object_t obj, void *mapping)
 {
+	vm_offset_t va;
 
+	va = (vm_offset_t)mapping;
+	pmap_qremove(va, 1);
+	kva_free(va, PAGE_SIZE);
 	vm_object_deallocate(obj);
 }
 

sys/compat/linux/linux_vdso.h

@@ -39,7 +39,7 @@ struct linux_vdso_sym {
 };
 
 vm_object_t __elfN(linux_shared_page_init)(char **);
-void	__elfN(linux_shared_page_fini)(vm_object_t);
+void	__elfN(linux_shared_page_fini)(vm_object_t, void *);
 void	__elfN(linux_vdso_fixup)(struct sysentvec *);
 void	__elfN(linux_vdso_reloc)(struct sysentvec *);
 void	__elfN(linux_vdso_sym_init)(struct linux_vdso_sym *);