commit 6625986f3a5c7989b45022413c851f611783f361
author Nick Kralevich <nnk@google.com> Fri Mar 16 13:06:12 2012 -0700
committer Nick Kralevich <nnk@google.com> Fri Mar 16 13:06:12 2012 -0700
tree de566f83421e8b4c31d7bab4fdbbc0e0ae51fe79
parent adb6989786dcc7248d51a3a5a76221b93951f84a

linker: initially reserved memory as PROT_NONE

When the dynamic linker loads a shared library into memory, it
initially allocates a chunk of memory. The memory is then carved
into smaller chunks for each LOAD region, and appropriate memory
protections applied.

Modify the initial memory allocation so that the pages are mapped
as PROT_NONE, rather than PROT_READ / PROT_EXEC. This ensures that
gaps between LOAD regions are not inadvertantly readable / executable.

(Long term, we should munmap() these gaps entirely)

Change-Id: If128a203ccc6fe12dcbbd2bfe0cf13a2045675af

linker/linker.c

diff --git a/linker/linker.c b/linker/linker.c
index 7463811..f365fb6 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -815,16 +815,15 @@
     return (unsigned)req_base;
 }
 
-/* alloc_mem_region
+/* reserve_mem_region
  *
  *     This function reserves a chunk of memory to be used for mapping in
- *     the shared library. We reserve the entire memory region here, and
+ *     a prelinked shared library. We reserve the entire memory region here, and
  *     then the rest of the linker will relocate the individual loadable
  *     segments into the correct locations within this memory range.
  *
  * Args:
- *     si->base: The requested base of the allocation. If 0, a sane one will be
- *               chosen in the range LIBBASE <= base < LIBLAST.
+ *     si->base: The requested base of the allocation.
  *     si->size: The size of the allocation.
  *
  * Returns:
@@ -834,7 +833,7 @@
 
 static int reserve_mem_region(soinfo *si)
 {
-    void *base = mmap((void *)si->base, si->size, PROT_READ | PROT_EXEC,
+    void *base = mmap((void *)si->base, si->size, PROT_NONE,
                       MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
     if (base == MAP_FAILED) {
         DL_ERR("%5d can NOT map (%sprelinked) library '%s' at 0x%08x "
@@ -852,8 +851,7 @@
     return 0;
 }
 
-static int
-alloc_mem_region(soinfo *si)
+static int alloc_mem_region(soinfo *si)
 {
     if (si->base) {
         /* Attempt to mmap a prelinked library. */
@@ -864,7 +862,7 @@
        allocator.
     */
 
-    void *base = mmap(NULL, si->size, PROT_READ | PROT_EXEC,
+    void *base = mmap(NULL, si->size, PROT_NONE,
                       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
     if (base == MAP_FAILED) {
         DL_ERR("%5d mmap of library '%s' failed: %d (%s)\n",