Clean up DSBT support

The existing DSBT support relies on the kernel to provide DSBT info
as part of the load maps passed to user space. The problem with this
approach is that the DSBT info is in the dynamic section, so the
kernel must access a userspace mapping of the dynamic section (or
separately read a copy for the kernel) in order to retrieve the
information needed by userspace.

This patch reworks the DSBT support to remove the reliance on DSBT
info coming from the kernel. Instead, ldso reads the info itself from
the dynamic section. One other benefit of this is that it allows the
existing kernel FDPIC loader to also load DSBT binaries.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

1 files changed, 34 insertions, 36 deletions

diff --git a/ldso/ldso/dl-elf.c b/ldso/ldso/dl-elf.c
index 9e2a12ce7..31ba11ffa 100644
--- a/ldso/ldso/dl-elf.c
+++ b/ldso/ldso/dl-elf.c
@@ -851,10 +851,15 @@ struct elf_resolve *_dl_load_elf_shared_library(unsigned rflags,
 	/* Handle DSBT initialization */
 	{
 		struct elf_resolve *t, *ref;
-		int idx = tpnt->loadaddr.map->dsbt_index;
-		unsigned *dsbt = tpnt->loadaddr.map->dsbt_table;
+		int idx = tpnt->dsbt_index;
+		void **dsbt = tpnt->dsbt_table;
 
-		if (idx == 0) {
+		/*
+		 * It is okay (required actually) to have zero idx for an executable.
+		 * This is the case when running ldso standalone and the program
+		 * is being mapped in via _dl_load_shared_library().
+		 */
+		if (idx == 0 && tpnt->libtype != elf_executable) {
 			if (!dynamic_info[DT_TEXTREL]) {
 				/* This DSO has not been assigned an index. */
 				_dl_dprintf(2, "%s: '%s' is missing a dsbt index assignment!\n",
@@ -869,9 +874,9 @@ struct elf_resolve *_dl_load_elf_shared_library(unsigned rflags,
 					break;
 				}
 			}
-			idx = tpnt->loadaddr.map->dsbt_size;
+			idx = tpnt->dsbt_size;
 			while (idx-- > 0)
-				if (!ref || ref->loadaddr.map->dsbt_table[idx] == NULL)
+				if (!ref || ref->dsbt_table[idx] == NULL)
 					break;
 			if (idx <= 0) {
 				_dl_dprintf(2, "%s: '%s' caused DSBT table overflow!\n",
@@ -880,43 +885,36 @@ struct elf_resolve *_dl_load_elf_shared_library(unsigned rflags,
 			}
 			_dl_if_debug_dprint("\n\tfile='%s';  assigned index %d\n",
 					    libname, idx);
-			tpnt->loadaddr.map->dsbt_index = idx;
+			tpnt->dsbt_index = idx;
+		}
 
+		/* make sure index is not already used */
+		if (_dl_ldso_dsbt[idx]) {
+			struct elf_resolve *dup;
+			const char *dup_name;
+
+			for (dup = _dl_loaded_modules; dup; dup = dup->next)
+				if (dup != tpnt && dup->dsbt_index == idx)
+					break;
+			if (dup)
+				dup_name = dup->libname;
+			else if (idx == 1)
+				dup_name = "runtime linker";
+			else
+				dup_name = "unknown library";
+			_dl_dprintf(2, "%s: '%s' dsbt index %d already used by %s!\n",
+				    _dl_progname, libname, idx, dup_name);
+			_dl_exit(1);
 		}
 
 		/*
 		 * Setup dsbt slot for this module in dsbt of all modules.
 		 */
-		ref = NULL;
-		for (t = _dl_loaded_modules; t; t = t->next) {
-			/* find a dsbt table from another module */
-			if (ref == NULL && t != tpnt) {
-				ref = t;
-
-				/* make sure index is not already used */
-				if (t->loadaddr.map->dsbt_table[idx]) {
-					struct elf_resolve *dup;
-					char *dup_name;
-
-					for (dup = _dl_loaded_modules; dup; dup = dup->next)
-						if (dup != tpnt && dup->loadaddr.map->dsbt_index == idx)
-							break;
-					if (dup)
-						dup_name = dup->libname;
-					else if (idx == 1)
-						dup_name = "runtime linker";
-					else
-						dup_name = "unknown library";
-					_dl_dprintf(2, "%s: '%s' dsbt index %d already used by %s!\n",
-						    _dl_progname, libname, idx, dup_name);
-					_dl_exit(1);
-				}
-			}
-			t->loadaddr.map->dsbt_table[idx] = (unsigned)dsbt;
-		}
-		if (ref)
-			_dl_memcpy(dsbt, ref->loadaddr.map->dsbt_table,
-				   tpnt->loadaddr.map->dsbt_size * sizeof(unsigned *));
+		for (t = _dl_loaded_modules; t; t = t->next)
+			t->dsbt_table[idx] = dsbt;
+		_dl_ldso_dsbt[idx] = dsbt;
+		_dl_memcpy(dsbt, _dl_ldso_dsbt,
+			   tpnt->dsbt_size * sizeof(tpnt->dsbt_table[0]));
 	}
 #endif
 	_dl_if_debug_dprint("\n\tfile='%s';  generating link map\n", libname);