From c210ef1347929cb3a0f46cdfdb3d4ad738e3af74 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 11 Nov 2021 20:07:44 +0200
Subject: [PATCH] rtld: load preloaded vdso

Reviewed by:	emaste
Discussed with:	jrtc27
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 month
Differential revision:	https://reviews.freebsd.org/D32960
---
 libexec/rtld-elf/rtld.c | 79 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
index af29d3ead390..5819bf18e4b5 100644
--- a/libexec/rtld-elf/rtld.c
+++ b/libexec/rtld-elf/rtld.c
@@ -125,6 +125,7 @@ static void load_filtees(Obj_Entry *, int flags, RtldLockState *);
 static void unload_filtees(Obj_Entry *, RtldLockState *);
 static int load_needed_objects(Obj_Entry *, int);
 static int load_preload_objects(const char *, bool);
+static int load_kpreload(const void *addr);
 static Obj_Entry *load_object(const char *, int fd, const Obj_Entry *, int);
 static void map_stacks_exec(RtldLockState *);
 static int obj_disable_relro(Obj_Entry *);
@@ -828,6 +829,13 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
     if (!libmap_disable)
         libmap_disable = (bool)lm_init(libmap_override);
 
+    if (aux_info[AT_KPRELOAD] != NULL &&
+      aux_info[AT_KPRELOAD]->a_un.a_ptr != NULL) {
+	dbg("loading kernel vdso");
+	if (load_kpreload(aux_info[AT_KPRELOAD]->a_un.a_ptr) == -1)
+	    rtld_die();
+    }
+
     dbg("loading LD_PRELOAD_FDS libraries");
     if (load_preload_objects(ld_preload_fds, true) == -1)
 	rtld_die();
@@ -2842,6 +2850,77 @@ do_load_object(int fd, const char *name, char *path, struct stat *sbp,
     return (NULL);
 }
 
+static int
+load_kpreload(const void *addr)
+{
+	Obj_Entry *obj;
+	const Elf_Ehdr *ehdr;
+	const Elf_Phdr *phdr, *phlimit, *phdyn, *seg0, *segn;
+	static const char kname[] = "[vdso]";
+
+	ehdr = addr;
+	if (!check_elf_headers(ehdr, "kpreload"))
+		return (-1);
+	obj = obj_new();
+	phdr = (const Elf_Phdr *)((const char *)addr + ehdr->e_phoff);
+	obj->phdr = phdr;
+	obj->phsize = ehdr->e_phnum * sizeof(*phdr);
+	phlimit = phdr + ehdr->e_phnum;
+	seg0 = segn = NULL;
+
+	for (; phdr < phlimit; phdr++) {
+		switch (phdr->p_type) {
+		case PT_DYNAMIC:
+			phdyn = phdr;
+			break;
+		case PT_GNU_STACK:
+			/* Absense of PT_GNU_STACK implies stack_flags == 0. */
+			obj->stack_flags = phdr->p_flags;
+			break;
+		case PT_LOAD:
+			if (seg0 == NULL || seg0->p_vaddr > phdr->p_vaddr)
+				seg0 = phdr;
+			if (segn == NULL || segn->p_vaddr + segn->p_memsz <
+			    phdr->p_vaddr + phdr->p_memsz)
+				segn = phdr;
+			break;
+		}
+	}
+
+	obj->mapbase = __DECONST(caddr_t, addr);
+	obj->mapsize = segn->p_vaddr + segn->p_memsz - (Elf_Addr)addr;
+	obj->vaddrbase = 0;
+	obj->relocbase = obj->mapbase;
+
+	object_add_name(obj, kname);
+	obj->path = xstrdup(kname);
+	obj->dynamic = (const Elf_Dyn *)(obj->relocbase + phdyn->p_vaddr);
+
+	if (!digest_dynamic(obj, 0)) {
+		obj_free(obj);
+		return (-1);
+	}
+
+	/*
+	 * We assume that kernel-preloaded object does not need
+	 * relocation.  It is currently written into read-only page,
+	 * handling relocations would mean we need to allocate at
+	 * least one additional page per AS.
+	 */
+	dbg("%s mapbase %p phdrs %p PT_LOAD phdr %p vaddr %p dynamic %p",
+	    obj->path, obj->mapbase, obj->phdr, seg0,
+	    obj->relocbase + seg0->p_vaddr, obj->dynamic);
+
+	TAILQ_INSERT_TAIL(&obj_list, obj, next);
+	obj_count++;
+	obj_loads++;
+	linkmap_add(obj);	/* for GDB & dlinfo() */
+	max_stack_flags |= obj->stack_flags;
+
+	LD_UTRACE(UTRACE_LOAD_OBJECT, obj, obj->mapbase, 0, 0, obj->path);
+	return (0);
+}
+
 Obj_Entry *
 obj_from_addr(const void *addr)
 {