am 91bc5865: am 8d01c055: am 1271cdc1: Merge "Revert "stack protector: use AT_RANDOM""

* commit '91bc5865a333212e7cac934b0a2ac7c522911d58':
  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
 

linker/linker.cpp

@@ -1785,7 +1785,7 @@ static bool soinfo_link_image(soinfo* si) {
  * fixed it's own GOT. It is safe to make references to externs
  * and other non-local data at this point.
  */
-static unsigned __linker_init_post_relocation(uintptr_t* elfdata, unsigned linker_base)
+static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base)
 {
     static soinfo linker_soinfo;
 
@@ -1976,7 +1976,7 @@ static unsigned __linker_init_post_relocation(uintptr_t* elfdata, unsigned linke
  * Find the value of AT_BASE passed to us by the kernel. This is the load
  * location of the linker.
  */
-static unsigned find_linker_base(uintptr_t* elfdata) {
+static unsigned find_linker_base(unsigned **elfdata) {
     int argc = (int) *elfdata;
     char **argv = (char**) (elfdata + 1);
     unsigned *vecs = (unsigned*) (argv + argc + 1);
@@ -2032,8 +2032,8 @@ get_elf_exec_load_bias(const Elf32_Ehdr* elf)
  * relocations, any attempt to reference an extern variable, extern
  * function, or other GOT reference will generate a segfault.
  */
-extern "C" unsigned __linker_init(uintptr_t* elfdata) {
-    uintptr_t linker_addr = find_linker_base(elfdata);
+extern "C" unsigned __linker_init(unsigned **elfdata) {
+    unsigned linker_addr = find_linker_base(elfdata);
     Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr;
     Elf32_Phdr *phdr =
         (Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff);

tests/stack_protector_test.cpp

@@ -56,7 +56,13 @@ struct stack_protector_checker {
 
     // Duplicate tid. gettid(2) bug? Seeing this would be very upsetting.
     ASSERT_TRUE(tids.find(tid) == tids.end());
-
+#ifdef __GLIBC__
+    // glibc uses the same guard for every thread. bionic uses a different guard for each one.
+#else
+    // Duplicate guard. Our bug. Note this is potentially flaky; we _could_ get the
+    // same guard for two threads, but it should be vanishingly unlikely.
+    ASSERT_TRUE(guards.find(guard) == guards.end());
+#endif
     // Uninitialized guard. Our bug. Note this is potentially flaky; we _could_ get
     // four random zero bytes, but it should be vanishingly unlikely.
     ASSERT_NE(guard, 0U);
@@ -72,7 +78,7 @@ static void* ThreadGuardHelper(void* arg) {
   return NULL;
 }
 
-TEST(stack_protector, same_guard_per_thread) {
+TEST(stack_protector, guard_per_thread) {
   stack_protector_checker checker;
   size_t thread_count = 10;
   for (size_t i = 0; i < thread_count; ++i) {
@@ -84,8 +90,12 @@ TEST(stack_protector, same_guard_per_thread) {
   }
   ASSERT_EQ(thread_count, checker.tids.size());
 
-  // bionic x86 and glibc uses the same guard for every thread.
+  // glibc uses the same guard for every thread. bionic uses a different guard for each one.
+#ifdef __BIONIC__
+  ASSERT_EQ(thread_count, checker.guards.size());
+#else
   ASSERT_EQ(1U, checker.guards.size());
+#endif
 }
 
 #endif