am 8d01c055: am 1271cdc1: Merge "Revert "stack protector: use AT_RANDOM""

* commit '8d01c0557bb2b7ea30f4038b6c84b816800073a7':
  Revert "stack protector: use AT_RANDOM"

libc/bionic/libc_init_common.c

@@ -53,22 +53,6 @@ unsigned int __page_shift = PAGE_SHIFT;
 
 int __system_properties_init(void);
 
-static Elf32_auxv_t* get_aux_from_elfdata(uintptr_t* elf_data) {
-  int argc = *elf_data;
-  char** argv = (char**) (elf_data + 1);
-  char** envp = argv + argc + 1;
-
-  // The auxiliary vector is at the end of the environment block
-  while(*envp != NULL) {
-    envp++;
-  }
-  /* The end of the environment block is marked by two NULL pointers */
-  envp++;
-
-  return (Elf32_auxv_t*) envp;
-}
-
-
 /* Init TLS for the initial thread. Called by the linker _before_ libc is mapped
  * in memory. Beware: all writes to libc globals from this function will
  * apply to linker-private copies and will not be visible from libc later on.
@@ -80,7 +64,7 @@ static Elf32_auxv_t* get_aux_from_elfdata(uintptr_t* elf_data) {
  * This function also stores the elf_data argument in a specific TLS slot to be later
  * picked up by the libc constructor.
  */
-void __libc_init_tls(uintptr_t* elf_data) {
+void __libc_init_tls(unsigned** elf_data) {
   unsigned stack_top = (__get_sp() & ~(PAGE_SIZE - 1)) + PAGE_SIZE;
   unsigned stack_size = 128 * 1024;
   unsigned stack_bottom = stack_top - stack_size;
@@ -93,7 +77,6 @@ void __libc_init_tls(uintptr_t* elf_data) {
   _init_thread(&thread, gettid(), &thread_attr, (void*) stack_bottom, false);
 
   static void* tls_area[BIONIC_TLS_SLOTS];
-  __libc_auxv = get_aux_from_elfdata(elf_data);
   __init_tls(tls_area, &thread);
   tls_area[TLS_SLOT_BIONIC_PREINIT] = elf_data;
 }
@@ -113,7 +96,14 @@ void __libc_init_common(uintptr_t* elf_data) {
   __progname = argv[0] ? argv[0] : "<unknown>";
   environ = envp;
 
-  __libc_auxv = get_aux_from_elfdata(elf_data);
+  // The auxiliary vector is at the end of the environment block
+  while(*envp != NULL) {
+    envp++;
+  }
+  /* The end of the environment block is marked by two NULL pointers */
+  envp++;
+
+  __libc_auxv = (Elf32_auxv_t*) envp;
 
   __system_properties_init(); // Requires 'environ'.
 }

libc/bionic/libc_init_static.c

@@ -96,7 +96,7 @@ __noreturn void __libc_init(uintptr_t *elfdata,
     int  argc;
     char **argv, **envp;
 
-    __libc_init_tls(elfdata);
+    __libc_init_tls(NULL);
 
     /* Initialize the C runtime environment */
     __libc_init_common(elfdata);

libc/private/bionic_ssp.h

@@ -29,8 +29,8 @@
 #ifndef _PRIVATE_SSP_H
 #define _PRIVATE_SSP_H
 
-#include <string.h>
-#include <sys/auxv.h>
+#include <errno.h>
+#include <sys/cdefs.h>
 
 __BEGIN_DECLS
 
@@ -48,11 +48,27 @@ extern void* __stack_chk_guard;
 extern void __stack_chk_fail();
 
 __inline__ static void* __attribute__((always_inline)) __generate_stack_chk_guard(void) {
+  union {
+    uintptr_t value;
+    char bytes[sizeof(uintptr_t)];
+  } u;
 
-  void* src = (void*) getauxval(AT_RANDOM);
-  void* result;
-  memcpy(&result, src, sizeof(result));
-  return result;
+  /* Try pulling random bytes from /dev/urandom. */
+  int fd = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY));
+  if (fd != -1) {
+    ssize_t byte_count = TEMP_FAILURE_RETRY(read(fd, &u.bytes, sizeof(u)));
+    close(fd);
+    if (byte_count == sizeof(u)) {
+      return (void*) u.value;
+    }
+  }
+
+  /* If that failed, switch to 'terminator canary'. */
+  u.bytes[0] = 0;
+  u.bytes[1] = 0;
+  u.bytes[2] = '\n';
+  u.bytes[3] = 255;
+  return (void*) u.value;
 }
 
 __END_DECLS

libc/private/bionic_tls.h

@@ -29,7 +29,6 @@
 #define _SYS_TLS_H
 
 #include <sys/cdefs.h>
-#include <stdint.h>
 
 __BEGIN_DECLS
 
@@ -135,7 +134,7 @@ extern void*  __get_tls( void );
 extern void*  __get_stack_base(int  *p_stack_size);
 
 /* Initialize the TLS. */
-extern void __libc_init_tls(uintptr_t* elfdata);
+extern void __libc_init_tls(unsigned** elfdata);
 
 __END_DECLS