Enable the service runtime to use a zero-based sandbox on Linux.

src/trusted/service_runtime/arch/arm/sel_addrspace_arm.c

Index: src/trusted/service_runtime/arch/arm/sel_addrspace_arm.c
diff --git a/src/trusted/service_runtime/arch/arm/sel_addrspace_arm.c b/src/trusted/service_runtime/arch/arm/sel_addrspace_arm.c
index 7283cd604598ce31c0daf3e8b4f7f7e3b38e426f..0db3d7b12609d9fb5f79dca850849c50004d5686 100644
--- a/src/trusted/service_runtime/arch/arm/sel_addrspace_arm.c
+++ b/src/trusted/service_runtime/arch/arm/sel_addrspace_arm.c
@@ -11,21 +11,53 @@
 #include "native_client/src/trusted/service_runtime/sel_memory.h"
 
 
-#define POST_ADDR_SPACE_GUARD_SIZE  (2 * NACL_PAGESIZE)
-
 /*
  * On ARM, we cheat slightly: we add two pages to the requested allocation!
  * This accomodates the guard region we require at the top end of untrusted
  * memory.
  */
+#define POST_ADDR_SPACE_GUARD_SIZE  (2 * NACL_PAGESIZE)
+
+/* NOTE: This routine is almost identical to the x86_32 version.
+ */
 NaClErrorCode NaClAllocateSpace(void **mem, size_t addrsp_size) {
-  CHECK(mem);
+  const void* ONE_MEGABYTE = (void *)1024*1024;

[Mark Seaborn, 2011/08/18 23:09:45]

Nit: " *" style not "* " in this code.

[Brad Chen, 2011/08/19 00:24:35]

Done.

+  int result;
+
+  CHECK(NULL != mem);
 
   addrsp_size += POST_ADDR_SPACE_GUARD_SIZE;
-  addrsp_size -= NACL_TRAMPOLINE_START;
+#if NACL_LINUX
+  /*
+   * On 32 bit Linux, a 1 gigabyte block of address space may be reserved at
+   * the zero-end of the address space during process creation, to address
+   * sandbox layout requirements on ARM and performance issues on Intel ATOM.
+   * Look for this pre-reserved block and if found, pass its address to the
+   * page allocation function.
+   */
+  if (!NaCl_find_prereserved_sandbox_memory(mem, addrsp_size)) {
+    /* zero-based sandbox not pre-reserved */

[Mark Seaborn, 2011/08/18 23:09:45]

Capitalise the start of the sentence, please.

[Brad Chen, 2011/08/19 00:24:35]

Done.

+    return LOAD_NO_MEMORY;
+  } else {
+    /* sanity check zero sandbox base address */

[Mark Seaborn, 2011/08/18 23:09:45]

Capitalise.

[Brad Chen, 2011/08/19 00:24:35]

Done.

+    if (0 == *mem || ONE_MEGABYTE > *mem)
+      return LOAD_NO_MEMORY;
 
-  *mem = (void *) NACL_TRAMPOLINE_START;
-  if (NaCl_page_alloc_at_addr(mem, addrsp_size) != 0) {
+    /*
+     * When creating a zero-based sandbox, we do not allocate the first 64K of
+     * pages beneath the trampolines, because -- on Linux at least -- we cannot.
+     * Instead, we allocate starting at the trampolines, and then coerce the
+     * "mem" out parameter.
+     */
+    addrsp_size -= NACL_TRAMPOLINE_START;
+    *mem = (void *) NACL_TRAMPOLINE_START;
+    result = NaCl_page_alloc_at_addr(mem, addrsp_size);
+    *mem = 0;
+  }
+#else
+# error "I only know how to allocate memory for ARM on Linux."
+#endif
+  if (0 != result) {
     NaClLog(2,
         "NaClAllocateSpace: NaCl_page_alloc_at_addr 0x%08"NACL_PRIxPTR
         " failed\n",
@@ -36,12 +68,6 @@ NaClErrorCode NaClAllocateSpace(void **mem, size_t addrsp_size) {
           (uintptr_t) *mem,
           addrsp_size);
 
-  /*
-   * makes sel_ldr think that the module's address space is at 0x0, this where
-   * it should be
-   */
-  *mem = 0x0;
-
   return LOAD_OK;
 }