The next step for mimmutable(). ld.so figures out what regions of memory

of startup shared library mappings can be made immutable, and also does
this for dlope() RTLD_NODELETE and subsidiary libraries.  Complexity in this
diff is due to the GNU_RELRO and OPENBSD_MUTABLE sections.
Tested in snaps for about 3 weeks, with some bootstrap related pain felt in ports
ok kettenis, much help from others.

1 files changed, 18 insertions, 3 deletions

diff --git a/libexec/ld.so/library_mquery.c b/libexec/ld.so/library_mquery.c
index 6903263b7f9..143c44c526b 100644
--- a/libexec/ld.so/library_mquery.c
+++ b/libexec/ld.so/library_mquery.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: library_mquery.c,v 1.68 2022/11/07 10:35:26 deraadt Exp $ */
+/*	$OpenBSD: library_mquery.c,v 1.69 2022/12/04 15:42:07 deraadt Exp $ */
 
 /*
  * Copyright (c) 2002 Dale Rahn
@@ -103,6 +103,7 @@ unload:
 elf_object_t *
 _dl_tryload_shlib(const char *libname, int type, int flags, int nodelete)
 {
+	struct mutate imut[MAXMUT], mut[MAXMUT];
 	int libfile, i;
 	struct load_list *ld, *lowld = NULL;
 	elf_object_t *object;
@@ -231,6 +232,8 @@ _dl_tryload_shlib(const char *libname, int type, int flags, int nodelete)
 #define LOFF ((Elf_Addr)lowld->start - lowld->moff)
 
 retry:
+	_dl_memset(&mut, 0, sizeof mut);
+	_dl_memset(&imut, 0, sizeof imut);
 	exec_start = NULL;
 	exec_size = 0;
 	for (ld = lowld; ld != NULL; ld = ld->next) {
@@ -285,6 +288,9 @@ retry:
 			exec_size = ROUND_PG(ld->size);
 		}
 
+		/* Entire mapping can become immutable, minus exceptions chosen later */
+		_dl_defer_immut(imut, LOFF + ld->moff, ROUND_PG(ld->size));
+
 		ld->start = res;
 	}
 
@@ -298,12 +304,19 @@ retry:
 
 	phdp = (Elf_Phdr *)(hbuf + ehdr->e_phoff);
 	for (i = 0; i < ehdr->e_phnum; i++, phdp++) {
-		if (phdp->p_type == PT_OPENBSD_RANDOMIZE)
+		switch (phdp->p_type) {
+		case PT_OPENBSD_RANDOMIZE:
 			_dl_arc4randombuf((char *)(phdp->p_vaddr + LOFF),
 			    phdp->p_memsz);
-		else if (phdp->p_type == PT_GNU_RELRO) {
+			break;
+		case PT_GNU_RELRO:
 			relro_addr = phdp->p_vaddr + LOFF;
 			relro_size = phdp->p_memsz;
+			_dl_defer_mut(mut, phdp->p_vaddr + LOFF, phdp->p_memsz);
+			break;
+		case PT_OPENBSD_MUTABLE:
+			_dl_defer_mut(mut, phdp->p_vaddr + LOFF, phdp->p_memsz);
+			break;
 		}
 	}
 
@@ -337,6 +350,8 @@ retry:
 				_dl_printf("msyscall %lx %lx error\n",
 				    exec_start, exec_size);
 		}
+		_dl_bcopy(mut, object->mut, sizeof mut);
+		_dl_bcopy(imut, object->imut, sizeof imut);
 	} else {
 		_dl_load_list_free(lowld);
 	}