TLS fixes, mainly alignment handling

compute offsets from the thread pointer statically when loading the
library, rather than repeating the logic on each thread creation. not
only is the latter less efficient at runtime; it also fails to provide
solid guarantees that the offsets will remain the same when the
initial alignment of memory is different. the new alignment handling
is both more rigorous and simpler.

the old code was also clobbering TLS bss with random image data in
some cases due to using tls_size (size of TLS segment) instead of
tls_len (length of the TLS data image).

1 files changed, 48 insertions, 39 deletions

diff --git a/src/ldso/dynlink.c b/src/ldso/dynlink.c
index e07db33a..21c3ebad 100644
--- a/src/ldso/dynlink.c
+++ b/src/ldso/dynlink.c
@@ -40,6 +40,9 @@ typedef Elf64_Sym Sym;
 #define R_SYM(x) ((x)>>32)
 #endif
 
+#define MAXP2(a,b) (-(-(a)&-(b)))
+#define ALIGN(x,y) ((x)+(y)-1 & -(y))
+
 struct debug {
 	int ver;
 	void *head;
@@ -97,7 +100,7 @@ static jmp_buf rtld_fail;
 static pthread_rwlock_t lock;
 static struct debug debug;
 static size_t *auxv;
-static size_t tls_cnt, tls_size;
+static size_t tls_cnt, tls_offset, tls_start, tls_align = 4*sizeof(size_t);
 static pthread_mutex_t init_fini_lock = { ._m_type = PTHREAD_MUTEX_RECURSIVE };
 
 struct debug *_dl_debug_addr = &debug;
@@ -525,8 +528,11 @@ static struct dso *load_library(const char *name)
 	if (pathname != name) p->shortname = strrchr(p->name, '/')+1;
 	if (p->tls_image) {
 		p->tls_id = ++tls_cnt;
-		tls_size += p->tls_size + p->tls_align + 8*sizeof(size_t) - 1
-			& -4*sizeof(size_t);
+		tls_align = MAXP2(tls_align, p->tls_align);
+		tls_offset += p->tls_size + p->tls_align - 1;
+		tls_offset -= (tls_offset + (uintptr_t)p->tls_image)
+			& (p->tls_align-1);
+		p->tls_offset = tls_offset;
 		p->new_dtv = (void *)(-sizeof(size_t) &
 			(uintptr_t)(p->name+strlen(p->name)+sizeof(size_t)));
 		p->new_tls = (void *)(p->new_dtv + n_th*(tls_cnt+1));
@@ -683,21 +689,26 @@ void _dl_debug_state(void)
 
 void *__copy_tls(unsigned char *mem)
 {
+	pthread_t td;
 	struct dso *p;
+
+	if (!tls_cnt) return mem;
+
 	void **dtv = (void *)mem;
 	dtv[0] = (void *)tls_cnt;
-	mem = (void *)(dtv + tls_cnt + 1);
-	for (p=tail; p; p=p->prev) {
+
+	mem += __libc.tls_size - sizeof(struct pthread);
+	mem -= (uintptr_t)mem & (tls_align-1);
+	mem -= tls_start;
+	td = (pthread_t)mem;
+
+	for (p=head; p; p=p->next) {
 		if (!p->tls_id) continue;
-		mem += -p->tls_len & (4*sizeof(size_t)-1);
-		mem += ((uintptr_t)p->tls_image - (uintptr_t)mem)
-			& (p->tls_align-1);
-		dtv[p->tls_id] = mem;
-		memcpy(mem, p->tls_image, p->tls_len);
-		mem += p->tls_size;
+		dtv[p->tls_id] = mem - p->tls_offset;
+		memcpy(dtv[p->tls_id], p->tls_image, p->tls_len);
 	}
-	((pthread_t)mem)->dtv = dtv;
-	return mem;
+	td->dtv = dtv;
+	return td;
 }
 
 void *__tls_get_addr(size_t *v)
@@ -737,11 +748,18 @@ void *__tls_get_addr(size_t *v)
 		(p->tls_size + p->tls_align) * a_fetch_add(&p->new_tls_idx,1);
 	mem += ((uintptr_t)p->tls_image - (uintptr_t)mem) & (p->tls_align-1);
 	self->dtv[v[0]] = mem;
-	memcpy(mem, p->tls_image, p->tls_size);
+	memcpy(mem, p->tls_image, p->tls_len);
 	pthread_sigmask(SIG_SETMASK, &set, 0);
 	return mem + v[1];
 }
 
+static void update_tls_size()
+{
+	size_t below_tp = (1+tls_cnt) * sizeof(void *) + tls_offset;
+	size_t above_tp = sizeof(struct pthread) + tls_start + tls_align;
+	__libc.tls_size = ALIGN(below_tp + above_tp, tls_align);
+}
+
 void *__dynlink(int argc, char **argv)
 {
 	size_t aux[AUX_CNT] = {0};
@@ -849,9 +867,11 @@ void *__dynlink(int argc, char **argv)
 		aux[AT_ENTRY] = ehdr->e_entry;
 	}
 	if (app->tls_size) {
-		app->tls_id = ++tls_cnt;
-		tls_size += app->tls_size+app->tls_align + 8*sizeof(size_t)-1
-			& -4*sizeof(size_t);
+		app->tls_id = tls_cnt = 1;
+		tls_offset = app->tls_offset = app->tls_size;
+		tls_start = -((uintptr_t)app->tls_image + app->tls_size)
+			& (app->tls_align-1);
+		tls_align = MAXP2(tls_align, app->tls_align);
 	}
 	app->global = 1;
 	app->constructed = 1;
@@ -900,12 +920,10 @@ void *__dynlink(int argc, char **argv)
 	load_deps(app);
 	make_global(app);
 
-	/* Make an initial pass setting up TLS before performing relocs.
-	 * This provides the TP-based offset of each DSO's TLS for
-	 * use in TP-relative relocations. After relocations, we need
-	 * to copy the TLS images again in case they had relocs. */
-	tls_size += sizeof(struct pthread) + 4*sizeof(size_t);
-	__libc.tls_size = tls_size;
+	reloc_all(app->next);
+	reloc_all(app);
+
+	update_tls_size();
 	if (tls_cnt) {
 		struct dso *p;
 		void *mem = mmap(0, __libc.tls_size, PROT_READ|PROT_WRITE,
@@ -913,23 +931,11 @@ void *__dynlink(int argc, char **argv)
 		if (mem==MAP_FAILED ||
 		    !__install_initial_tls(__copy_tls(mem))) {
 			dprintf(2, "%s: Error getting %zu bytes thread-local storage: %m\n",
-				argv[0], tls_size);
+				argv[0], __libc.tls_size);
 			_exit(127);
 		}
-		for (p=head; p; p=p->next) {
-			if (!p->tls_id) continue;
-			p->tls_offset = (char *)__pthread_self()
-				- (char *)__pthread_self()->dtv[p->tls_id];
-		}
 	}
 
-	reloc_all(app->next);
-	reloc_all(app);
-
-	/* The initial DTV is located at the base of the memory
-	 * allocated for TLS. Repeat copying TLS to pick up relocs. */
-	if (tls_cnt) __copy_tls((void *)__pthread_self()->dtv);
-
 	if (ldso_fail) _exit(127);
 	if (ldd_mode) _exit(0);
 
@@ -963,7 +969,7 @@ void *__dynlink(int argc, char **argv)
 void *dlopen(const char *file, int mode)
 {
 	struct dso *volatile p, *orig_tail, *next;
-	size_t orig_tls_cnt;
+	size_t orig_tls_cnt, orig_tls_offset, orig_tls_align;
 	size_t i;
 	int cs;
 
@@ -975,6 +981,8 @@ void *dlopen(const char *file, int mode)
 
 	p = 0;
 	orig_tls_cnt = tls_cnt;
+	orig_tls_offset = tls_offset;
+	orig_tls_align = tls_align;
 	orig_tail = tail;
 
 	if (setjmp(rtld_fail)) {
@@ -989,7 +997,8 @@ void *dlopen(const char *file, int mode)
 			free(p);
 		}
 		tls_cnt = orig_tls_cnt;
-		tls_size = __libc.tls_size;
+		tls_offset = orig_tls_offset;
+		tls_align = orig_tls_align;
 		tail = orig_tail;
 		tail->next = 0;
 		p = 0;
@@ -1024,7 +1033,7 @@ void *dlopen(const char *file, int mode)
 		p->global = 1;
 	}
 
-	__libc.tls_size = tls_size;
+	update_tls_size();
 
 	if (ssp_used) __init_ssp(auxv);