malloc: Implement heap protector

2016-10-27  Florian Weimer  <fweimer@redhat.com>

	* malloc/mallc-internal.h (__malloc_header_guard)
	(__malloc_footer_guard): Declare.
	* malloc/malloc-guard.c: New file.
	* malloc/Makefile (routines): Add it.
	* malloc/malloc.c (HEAP_CRYPT_SIZE, HEAP_CRYPT_PREVSIZE): Define.
	(chunksize_nomask, prev_size, set_prev_size, set_head_size)
	(set_head, set_foot): Add encryption.
	* malloc/arena.c (ptmalloc_init): For shared builds, initialize
	the heap guard variables.  Initialize the top chunk.
	* malloc/hooks.c (malloc_set_state): Apply the heap guard to the
	dumped heap.
	* malloc/tst-mallocstate.c (malloc_usable_size_valid): New
	variable.
	(check_allocation): Check malloc_usable_size result if
	malloc_usable_size_valid.
	(init_heap): Set malloc_usable_size_valid.
	* csu/libc-start.c (LIBC_START_MAIN): Initialize heap guard
	variables.
	* sysdeps/generic/ldsodefs.h (struct rtld_global_ro): Add members
	_dl_malloc_header_guard, _dl_malloc_footer_guard.
	* elf/rtld.c (security_init): Initialize temporary copy of the
	heap guard variables.

diff --git a/csu/libc-start.c b/csu/libc-start.c
index 333a4cc..ae6abde 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -22,6 +22,7 @@
 #include <ldsodefs.h>
 #include <exit-thread.h>
 #include <elf/dl-keysetup.h>
+#include <malloc/malloc-internal.h>
 
 extern void __libc_init_first (int argc, char **argv, char **envp);
 
@@ -210,6 +211,11 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
   __pointer_chk_guard_local = keys.pointer;
 # endif
 
+  /* In the non-shared case, we initialize the heap guard
+     directly.  */
+  __malloc_header_guard = keys.heap_header;
+  __malloc_footer_guard = keys.heap_footer;
+
 #endif
 
   /* Register the destructor of the dynamic linker if there is any.  */
diff --git a/elf/rtld.c b/elf/rtld.c
index de965da..7ea06e4 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -42,6 +42,7 @@
 #include <stap-probe.h>
 #include <stackinfo.h>
 #include <dl-keysetup.h>
+#include <malloc/malloc-internal.h>
 
 #include <assert.h>
 
@@ -716,6 +717,11 @@ security_init (void)
 #endif
   __pointer_chk_guard_local = keys.pointer;
 
+  /* Keep a copy of the computed keys, so that they can be obtained
+     during malloc initialization in libc.so.  */
+  GLRO (dl_malloc_header_guard) = keys.heap_header;
+  GLRO (dl_malloc_footer_guard) = keys.heap_footer;
+
   /* We do not need the _dl_random value anymore.  The less
      information we leave behind, the better, so clear the
      variable.  */
diff --git a/malloc/Makefile b/malloc/Makefile
index b8efcd6..cd289f8 100644
--- a/malloc/Makefile
+++ b/malloc/Makefile
@@ -41,7 +41,7 @@ tests-static := \
 tests += $(tests-static)
 test-srcs = tst-mtrace
 
-routines = malloc morecore mcheck mtrace obstack \
+routines = malloc morecore mcheck mtrace obstack malloc-guard \
   scratch_buffer_grow scratch_buffer_grow_preserve \
   scratch_buffer_set_array_size
 
diff --git a/malloc/arena.c b/malloc/arena.c
index f85b0af..792451a 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -340,6 +340,19 @@ ptmalloc_init (void)
       if (check_action != 0)
         __malloc_check_init ();
     }
+
+#ifdef SHARED
+  /* For a shared library, elf/rtld.c performed key setup in
+     security_init, and we copy the keys.  In static builds, the guard
+     cookies have already been initialized in csu/libc-start.c.  */
+  __malloc_header_guard = GLRO (dl_malloc_header_guard);
+  __malloc_footer_guard = GLRO (dl_malloc_footer_guard);
+#endif
+
+  /* Initialize the top chunk, based on the heap protector guards.  */
+  malloc_init_state (&main_arena);
+  set_head (main_arena.top, 0);
+
 #if HAVE_MALLOC_INIT_HOOK
   void (*hook) (void) = atomic_forced_read (__malloc_initialize_hook);
   if (hook != NULL)
diff --git a/malloc/hooks.c b/malloc/hooks.c
index 12995d3..8bb2b74 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -537,35 +537,38 @@ malloc_set_state (void *msptr)
      dumped_main_arena_end, realloc and free will recognize these
      chunks as dumped fake mmapped chunks and never free them.  */
 
-  /* Find the chunk with the lowest address with the heap.  */
-  mchunkptr chunk = NULL;
+  /* Find the chunk with the lowest address with the heap.  If
+     successful, size_header will point to the mchunk_size member (not
+     the chunk start, i.e. the mchunck_prev_size member).  */
+  size_t *size_header = NULL;
   {
     size_t *candidate = (size_t *) ms->sbrk_base;
     size_t *end = (size_t *) (ms->sbrk_base + ms->sbrked_mem_bytes);
     while (candidate < end)
       if (*candidate != 0)
 	{
-	  chunk = mem2chunk ((void *) (candidate + 1));
+	  size_header = candidate;
 	  break;
 	}
       else
 	++candidate;
   }
-  if (chunk == NULL)
+  if (size_header == NULL)
     return 0;
 
   /* Iterate over the dumped heap and patch the chunks so that they
-     are treated as fake mmapped chunks.  */
+     are treated as fake mmapped chunks.  We cannot use the regular
+     accessors because the chunks we read are not yet encrypted.  */
   mchunkptr top = ms->av[2];
-  while (chunk < top)
+  size_t *top_size_header = ((size_t *) top) + 1;
+  while (size_header < top_size_header)
     {
-      if (inuse (chunk))
-	{
-	  /* Mark chunk as mmapped, to trigger the fallback path.  */
-	  size_t size = chunksize (chunk);
-	  set_head (chunk, size | IS_MMAPPED);
-	}
-      chunk = next_chunk (chunk);
+      size_t size = *size_header & ~SIZE_BITS;
+      /* We treat all chunks as allocated.  The heap consistency
+	 checks do not trigger because they are not active for the
+	 dumped heap.  */
+      *size_header = HEAP_CRYPT_SIZE (size) | IS_MMAPPED;
+      size_header += size / sizeof (*size_header);
     }
 
   /* The dumped fake mmapped chunks all lie in this address range.  */
diff --git a/malloc/malloc-guard.c b/malloc/malloc-guard.c
new file mode 100644
index 0000000..c8b3581
--- /dev/null
+++ b/malloc/malloc-guard.c
@@ -0,0 +1,29 @@
+/* Heap protector variables.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+/* These variables are defined in a separate file because the static
+   startup code initializes them, but this should not pull the rest of
+   the libc malloc implementation into the link.  */
+
+#include <malloc-internal.h>
+
+/* The heap cookie.  The lowest three bits (corresponding to
+   SIZE_BITS) in __malloc_guard_header must be clear.  Initialized
+   during libc startup, and computed by elf/dl-keysetup.c.  */
+INTERNAL_SIZE_T __malloc_header_guard; /* For size.  */
+INTERNAL_SIZE_T __malloc_footer_guard; /* For prev_size.  */
diff --git a/malloc/malloc-internal.h b/malloc/malloc-internal.h
index a3df8c3..e723539 100644
--- a/malloc/malloc-internal.h
+++ b/malloc/malloc-internal.h
@@ -81,5 +81,8 @@ void __malloc_fork_unlock_parent (void) internal_function attribute_hidden;
 /* Called in the child process after a fork.  */
 void __malloc_fork_unlock_child (void) internal_function attribute_hidden;
 
+/* Random values for the heap protector.  */
+extern INTERNAL_SIZE_T __malloc_header_guard attribute_hidden;
+extern INTERNAL_SIZE_T __malloc_footer_guard attribute_hidden;
 
 #endif /* _MALLOC_INTERNAL_H */
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 72d22bd..e1e732d 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1221,6 +1221,10 @@ nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 /* Mark a chunk as not being on the main arena.  */
 #define set_non_main_arena(p) ((p)->mchunk_size |= NON_MAIN_ARENA)
 
+/* Decrypt a heap header chunk.  */
+#define HEAP_CRYPT_SIZE(val) (__malloc_header_guard ^ ((INTERNAL_SIZE_T) val))
+#define HEAP_CRYPT_PREVSIZE(val) \
+  (__malloc_footer_guard ^ ((INTERNAL_SIZE_T) val))
 
 /*
    Bits to mask off when extracting size
@@ -1236,16 +1240,16 @@ nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 #define chunksize(p) (chunksize_nomask (p) & ~(SIZE_BITS))
 
 /* Like chunksize, but do not mask SIZE_BITS.  */
-#define chunksize_nomask(p)         ((p)->mchunk_size)
+#define chunksize_nomask(p) HEAP_CRYPT_SIZE ((p)->mchunk_size)
 
 /* Ptr to next physical malloc_chunk. */
 #define next_chunk(p) ((mchunkptr) (((char *) (p)) + chunksize (p)))
 
 /* Size of the chunk below P.  Only valid if prev_inuse (P).  */
-#define prev_size(p) ((p)->mchunk_prev_size)
+#define prev_size(p) HEAP_CRYPT_PREVSIZE ((p)->mchunk_prev_size)
 
 /* Set the size of the chunk below P.  Only valid if prev_inuse (P).  */
-#define set_prev_size(p, sz) ((p)->mchunk_prev_size = (sz))
+#define set_prev_size(p, sz) ((p)->mchunk_prev_size = HEAP_CRYPT_PREVSIZE (sz))
 
 /* Ptr to previous physical malloc_chunk.  Only valid if prev_inuse (P).  */
 #define prev_chunk(p) ((mchunkptr) (((char *) (p)) - prev_size (p)))
@@ -1277,13 +1281,16 @@ nextchunk-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
 /* Set size at head, without disturbing its use bit */
-#define set_head_size(p, s)  ((p)->mchunk_size = (((p)->mchunk_size & SIZE_BITS) | (s)))
+#define set_head_size(p, s) \
+  ((p)->mchunk_size = ((p)->mchunk_size & SIZE_BITS) | HEAP_CRYPT_SIZE (s))
 
 /* Set size/use field */
-#define set_head(p, s)       ((p)->mchunk_size = (s))
+#define set_head(p, s) ((p)->mchunk_size = HEAP_CRYPT_SIZE (s))
 
 /* Set size at footer (only when chunk is not in use) */
-#define set_foot(p, s)       (((mchunkptr) ((char *) (p) + (s)))->mchunk_prev_size = (s))
+#define set_foot(p, s) \
+  (((mchunkptr) ((char *) (p) + (s)))->mchunk_prev_size \
+    = HEAP_CRYPT_PREVSIZE (s))
 
 
 #pragma GCC poison mchunk_size
diff --git a/malloc/tst-mallocstate.c b/malloc/tst-mallocstate.c
index 7e081c5..bd6678e 100644
--- a/malloc/tst-mallocstate.c
+++ b/malloc/tst-mallocstate.c
@@ -186,6 +186,10 @@ struct allocation
   unsigned int seed;
 };
 
+/* After heap initialization, we can call malloc_usable_size to check
+   if it gives valid results.  */
+static bool malloc_usable_size_valid;
+
 /* Check that the allocation task allocation has the expected
    contents.  */
 static void
@@ -221,6 +225,23 @@ check_allocation (const struct allocation *alloc, int index)
       putc ('\n', stdout);
       errors = true;
     }
+
+  if (malloc_usable_size_valid)
+    {
+      size_t usable = malloc_usable_size (alloc->data);
+      if (usable < size)
+        {
+          printf ("error: allocation %d has reported size %zu (expected %zu)\n",
+                  index, usable, size);
+          errors = true;
+        }
+      else if (usable > size + 4096)
+        {
+          printf ("error: allocation %d reported as %zu bytes (requested %zu)\n",
+                  index, usable, size);
+          errors = true;
+        }
+    }
 }
 
 /* A heap allocation combined with pending actions on it.  */
@@ -317,6 +338,10 @@ init_heap (void)
       write_message ("error: malloc_set_state failed\n");
       _exit (1);
     }
+
+  /* The heap has been initialized.  We may now call
+     malloc_usable_size.  */
+  malloc_usable_size_valid = true;
 }
 
 /* Interpose the initialization callback.  */
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index f68fdf4..801ded8 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -607,6 +607,10 @@ struct rtld_global_ro
   /* List of auditing interfaces.  */
   struct audit_ifaces *_dl_audit;
   unsigned int _dl_naudit;
+
+  /* malloc protection keys. */
+  uintptr_t _dl_malloc_header_guard;
+  uintptr_t _dl_malloc_footer_guard;
 };
 # define __rtld_global_attribute__
 # if IS_IN (rtld)
