From e13a2b8953efabd38edfb7637fda08638454c001 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Timo=20Ter=C3=A4s?= <timo.teras@iki.fi>
Date: Tue, 25 Mar 2014 14:13:27 +0200
Subject: [PATCH] implement PT_GNU_RELRO support

---
 src/ldso/dynlink.c | 52 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 15 deletions(-)

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index 616dc3e1..de0f2ac8 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -74,6 +74,7 @@ struct dso {
 	char *rpath_orig, *rpath;
 	void *tls_image;
 	size_t tls_len, tls_size, tls_align, tls_id, tls_offset;
+	size_t relro_start, relro_end;
 	void **new_dtv;
 	unsigned char *new_tls;
 	int new_dtv_idx, new_tls_idx;
@@ -281,27 +282,29 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
  * and "donate" them to the heap by setting up minimal malloc
  * structures and then freeing them. */
 
-static void reclaim(unsigned char *base, size_t start, size_t end)
+static void reclaim(struct dso *dso, size_t start, size_t end)
 {
 	size_t *a, *z;
+	if (start >= dso->relro_start && start < dso->relro_end) start = dso->relro_end;
+	if (end   >= dso->relro_start && end   < dso->relro_end) end = dso->relro_start;
 	start = start + 6*sizeof(size_t)-1 & -4*sizeof(size_t);
 	end = (end & -4*sizeof(size_t)) - 2*sizeof(size_t);
 	if (start>end || end-start < 4*sizeof(size_t)) return;
-	a = (size_t *)(base + start);
-	z = (size_t *)(base + end);
+	a = (size_t *)(dso->base + start);
+	z = (size_t *)(dso->base + end);
 	a[-2] = 1;
 	a[-1] = z[0] = end-start + 2*sizeof(size_t) | 1;
 	z[1] = 1;
 	free(a);
 }
 
-static void reclaim_gaps(unsigned char *base, Phdr *ph, size_t phent, size_t phcnt)
+static void reclaim_gaps(struct dso *dso, Phdr *ph, size_t phent, size_t phcnt)
 {
 	for (; phcnt--; ph=(void *)((char *)ph+phent)) {
 		if (ph->p_type!=PT_LOAD) continue;
 		if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
-		reclaim(base, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
-		reclaim(base, ph->p_vaddr+ph->p_memsz,
+		reclaim(dso, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
+		reclaim(dso, ph->p_vaddr+ph->p_memsz,
 			ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
 	}
 }
@@ -346,11 +349,14 @@ static void *map_library(int fd, struct dso *dso)
 	for (i=eh->e_phnum; i; i--, ph=(void *)((char *)ph+eh->e_phentsize)) {
 		if (ph->p_type == PT_DYNAMIC)
 			dyn = ph->p_vaddr;
-		if (ph->p_type == PT_TLS) {
+		else if (ph->p_type == PT_TLS) {
 			tls_image = ph->p_vaddr;
 			dso->tls_align = ph->p_align;
 			dso->tls_len = ph->p_filesz;
 			dso->tls_size = ph->p_memsz;
+		} else if (ph->p_type == PT_GNU_RELRO) {
+			dso->relro_start = ph->p_vaddr & -PAGE_SIZE;
+			dso->relro_end = (ph->p_vaddr + ph->p_memsz) & -PAGE_SIZE;
 		}
 		if (ph->p_type != PT_LOAD) continue;
 		if (ph->p_vaddr < addr_min) {
@@ -419,12 +425,12 @@ static void *map_library(int fd, struct dso *dso)
 				goto error;
 			break;
 		}
-	if (!runtime) reclaim_gaps(base, ph0, eh->e_phentsize, eh->e_phnum);
 	dso->map = map;
 	dso->map_len = map_len;
 	dso->base = base;
 	dso->dynv = (void *)(base+dyn);
 	if (dso->tls_size) dso->tls_image = (void *)(base+tls_image);
+	if (!runtime) reclaim_gaps(dso, ph0, eh->e_phentsize, eh->e_phnum);
 	free(allocated_buf);
 	return map;
 noexec:
@@ -766,6 +772,17 @@ static void reloc_all(struct dso *p)
 			2+(dyn[DT_PLTREL]==DT_RELA));
 		do_relocs(p, (void *)(p->base+dyn[DT_REL]), dyn[DT_RELSZ], 2);
 		do_relocs(p, (void *)(p->base+dyn[DT_RELA]), dyn[DT_RELASZ], 3);
+
+		if (p->relro_start != p->relro_end &&
+		    mprotect(p->base+p->relro_start, p->relro_end-p->relro_start, PROT_READ) < 0) {
+			snprintf(errbuf, sizeof errbuf,
+				"Error relocating %s: RELRO protection failed",
+				p->name);
+			if (runtime) longjmp(*rtld_fail, 1);
+			dprintf(2, "%s\n", errbuf);
+			ldso_fail = 1;
+		}
+
 		p->relocated = 1;
 	}
 }
@@ -782,6 +799,10 @@ static void find_map_range(Phdr *ph, size_t cnt, size_t stride, struct dso *p)
 {
 	size_t min_addr = -1, max_addr = 0;
 	for (; cnt--; ph = (void *)((char *)ph + stride)) {
+		if (ph->p_type == PT_GNU_RELRO) {
+			p->relro_start = ph->p_vaddr & -PAGE_SIZE;
+			p->relro_end = (ph->p_vaddr + ph->p_memsz) & -PAGE_SIZE;
+		}
 		if (ph->p_type != PT_LOAD) continue;
 		if (ph->p_vaddr < min_addr)
 			min_addr = ph->p_vaddr;
@@ -1133,9 +1154,9 @@ void *__dynlink(int argc, char **argv)
 	/* PAST THIS POINT, ALL LIBC INTERFACES ARE FULLY USABLE. */
 
 	/* Donate unused parts of app and library mapping to malloc */
-	reclaim_gaps(app->base, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
+	reclaim_gaps(app, (void *)aux[AT_PHDR], aux[AT_PHENT], aux[AT_PHNUM]);
 	ehdr = (void *)lib->base;
-	reclaim_gaps(lib->base, (void *)(lib->base+ehdr->e_phoff),
+	reclaim_gaps(lib, (void *)(lib->base+ehdr->e_phoff),
 		ehdr->e_phentsize, ehdr->e_phnum);
 
 	/* Load preload/needed libraries, add their symbols to the global
@@ -1146,6 +1167,12 @@ void *__dynlink(int argc, char **argv)
 	load_deps(app);
 	make_global(app);
 
+#ifndef DYNAMIC_IS_RO
+	for (i=0; app->dynv[i]; i+=2)
+		if (app->dynv[i]==DT_DEBUG)
+			app->dynv[i+1] = (size_t)&debug;
+#endif
+
 	reloc_all(app->next);
 	reloc_all(app);
 
@@ -1174,11 +1201,6 @@ void *__dynlink(int argc, char **argv)
 	 * all memory used by the dynamic linker. */
 	runtime = 1;
 
-#ifndef DYNAMIC_IS_RO
-	for (i=0; app->dynv[i]; i+=2)
-		if (app->dynv[i]==DT_DEBUG)
-			app->dynv[i+1] = (size_t)&debug;
-#endif
 	debug.ver = 1;
 	debug.bp = _dl_debug_state;
 	debug.head = head;
-- 
2.25.1