Revert 98909 - Use chain-loading for Linux nacl_helper

chrome/nacl/nacl_helper_bootstrap_linux.c

 /* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
- * This is a standalone program that loads and runs the dynamic linker.
- * This program itself must be linked statically.  To keep it small, it's
- * written to avoid all dependencies on libc and standard startup code.
- * Hence, this should be linked using -nostartfiles.  It must be compiled
- * with -fno-stack-protector to ensure the compiler won't emit code that
- * presumes some special setup has been done.
- *
- * On ARM, the compiler will emit calls to some libc functions, so we
- * cannot link with -nostdlib.  The functions it does use (memset and
- * __aeabi_* functions for integer division) are sufficiently small and
- * self-contained in ARM's libc.a that we don't have any problem using
- * the libc definitions though we aren't using the rest of libc or doing
- * any of the setup it might expect.
+ * Bootstraping the nacl_helper. This executable reserves the bottom 1G
+ * of the address space, then invokes nacl_helper_init. Note that,
+ * as the text of this executable will eventually be overwritten by the
+ * native_client module, nacl_helper_init must not attempt to return.
  */
 
-#include <elf.h>
-#include <fcntl.h>
-#include <link.h>
-#include <stddef.h>
-#include <stdint.h>
-#include <sys/mman.h>
+#include <stdlib.h>
 
-#define MAX_PHNUM               12
+/* reserve 1GB of space */
+#define ONEGIG (1 << 30)
+char nacl_reserved_space[ONEGIG];
 
-#if defined(__i386__)
-# define DYNAMIC_LINKER "/lib/ld-linux.so.2"
-#elif defined(__x86_64__)
-# define DYNAMIC_LINKER "/lib64/ld-linux-x86-64.so.2"
-#elif defined(__ARM_EABI__)
-# define DYNAMIC_LINKER "/lib/ld-linux.so.3"
-#else
-# error "Don't know the dynamic linker file name for this architecture!"
-#endif
+void nacl_helper_init(int argc, char *argv[],
+                      const char *nacl_reserved_space);
 
-
-/*
- * We're not using <string.h> functions here, to avoid dependencies.
- * In the x86 libc, even "simple" functions like memset and strlen can
- * depend on complex startup code, because in newer libc
- * implementations they are defined using STT_GNU_IFUNC.
- */
-
-static void my_bzero(void *buf, size_t n) {
-  char *p = buf;
-  while (n-- > 0)
-    *p++ = 0;
+int main(int argc, char *argv[]) {
+  nacl_helper_init(argc, argv, nacl_reserved_space);
+  abort();
+  return 0;  // convince the tools I'm sane.
 }
-
-static size_t my_strlen(const char *s) {
-  size_t n = 0;
-  while (*s++ != '\0')
-    ++n;
-  return n;
-}
-
-
-/*
- * Get inline functions for system calls.
- */
-static int my_errno;
-#define SYS_ERRNO my_errno
-#include "third_party/lss/linux_syscall_support.h"
-
-
-/*
- * We're avoiding libc, so no printf.  The only nontrivial thing we need
- * is rendering numbers, which is, in fact, pretty trivial.
- */
-static void iov_int_string(int value, struct kernel_iovec *iov,
-                           char *buf, size_t bufsz) {
-  char *p = &buf[bufsz];
-  do {
-    --p;
-    *p = "0123456789"[value % 10];
-    value /= 10;
-  } while (value != 0);
-  iov->iov_base = p;
-  iov->iov_len = &buf[bufsz] - p;
-}
-
-#define STRING_IOV(string_constant, cond) \
-  { (void *) string_constant, cond ? (sizeof(string_constant) - 1) : 0 }
-
-__attribute__((noreturn)) static void fail(const char *message,
-                                           const char *item1, int value1,
-                                           const char *item2, int value2) {
-  char valbuf1[32];
-  char valbuf2[32];
-  struct kernel_iovec iov[] = {
-    STRING_IOV("bootstrap_helper", 1),
-    STRING_IOV(DYNAMIC_LINKER, 1),
-    STRING_IOV(": ", 1),
-    { (void *) message, my_strlen(message) },
-    { (void *) item1, item1 == NULL ? 0 : my_strlen(item1) },
-    STRING_IOV("=", item1 != NULL),
-    {},
-    STRING_IOV(", ", item1 != NULL && item2 != NULL),
-    { (void *) item2, item2 == NULL ? 0 : my_strlen(item2) },
-    STRING_IOV("=", item2 != NULL),
-    {},
-    { "\n", 1 },
-  };
-  const int niov = sizeof(iov) / sizeof(iov[0]);
-
-  if (item1 != NULL)
-    iov_int_string(value1, &iov[6], valbuf1, sizeof(valbuf1));
-  if (item2 != NULL)
-    iov_int_string(value1, &iov[10], valbuf2, sizeof(valbuf2));
-
-  sys_writev(2, iov, niov);
-  sys_exit_group(2);
-  while (1) *(volatile int *) 0 = 0;  /* Crash.  */
-}
-
-
-static int my_open(const char *file, int oflag) {
-  int result = sys_open(file, oflag, 0);
-  if (result < 0)
-    fail("Cannot open dynamic linker!  ", "errno", my_errno, NULL, 0);
-  return result;
-}
-
-static void my_pread(const char *fail_message,
-                     int fd, void *buf, size_t bufsz, uintptr_t pos) {
-  ssize_t result = sys_pread64(fd, buf, bufsz, pos);
-  if (result < 0)
-    fail(fail_message, "errno", my_errno, NULL, 0);
-  if ((size_t) result != bufsz)
-    fail(fail_message, "read count", result, NULL, 0);
-}
-
-static uintptr_t my_mmap(const char *segment_type, unsigned int segnum,
-                         uintptr_t address, size_t size,
-                         int prot, int flags, int fd, uintptr_t pos) {
-#if defined(__NR_mmap2)
-  void *result = sys_mmap2((void *) address, size, prot, flags, fd, pos >> 12);
-#else
-  void *result = sys_mmap((void *) address, size, prot, flags, fd, pos);
-#endif
-  if (result == MAP_FAILED)
-    fail("Failed to map from dynamic linker!  ",
-         segment_type, segnum, "errno", my_errno);
-  return (uintptr_t) result;
-}
-
-static void my_mprotect(unsigned int segnum,
-                        uintptr_t address, size_t size, int prot) {
-  if (sys_mprotect((void *) address, size, prot) < 0)
-    fail("Failed to mprotect hole in dynamic linker!  ",
-         "segment", segnum, "errno", my_errno);
-}
-
-
-static int prot_from_phdr(const ElfW(Phdr) *phdr) {
-  int prot = 0;
-  if (phdr->p_flags & PF_R)
-    prot |= PROT_READ;
-  if (phdr->p_flags & PF_W)
-    prot |= PROT_WRITE;
-  if (phdr->p_flags & PF_X)
-    prot |= PROT_EXEC;
-  return prot;
-}
-
-static uintptr_t round_up(uintptr_t value, uintptr_t size) {
-  return (value + size - 1) & -size;
-}
-
-static uintptr_t round_down(uintptr_t value, uintptr_t size) {
-  return value & -size;
-}
-
-/*
- * Handle the "bss" portion of a segment, where the memory size
- * exceeds the file size and we zero-fill the difference.  For any
- * whole pages in this region, we over-map anonymous pages.  For the
- * sub-page remainder, we zero-fill bytes directly.
- */
-static void handle_bss(unsigned int segnum, const ElfW(Phdr) *ph,
-                       ElfW(Addr) load_bias, size_t pagesize) {
-  if (ph->p_memsz > ph->p_filesz) {
-    ElfW(Addr) file_end = ph->p_vaddr + load_bias + ph->p_filesz;
-    ElfW(Addr) file_page_end = round_up(file_end, pagesize);
-    ElfW(Addr) page_end = round_up(ph->p_vaddr + load_bias +
-                                   ph->p_memsz, pagesize);
-    if (page_end > file_page_end)
-      my_mmap("bss segment", segnum,
-              file_page_end, page_end - file_page_end,
-              prot_from_phdr(ph), MAP_ANON | MAP_PRIVATE | MAP_FIXED, -1, 0);
-    if (file_page_end > file_end && (ph->p_flags & PF_W))
-      my_bzero((void *) file_end, file_page_end - file_end);
-  }
-}
-
-/*
- * This is the main loading code.  It's called with the address of the
- * auxiliary vector on the stack, which we need to examine and modify.
- * It returns the dynamic linker's runtime entry point address, where
- * we should jump to.  This is called by the machine-dependent _start
- * code (below).  On return, it restores the original stack pointer
- * and jumps to this entry point.
- */
-ElfW(Addr) do_load(ElfW(auxv_t) *auxv) {
-  /*
-   * Record the auxv entries that are specific to the file loaded.
-   * The incoming entries point to our own static executable.
-   */
-  ElfW(auxv_t) *av_entry = NULL;
-  ElfW(auxv_t) *av_phdr = NULL;
-  ElfW(auxv_t) *av_phnum = NULL;
-  size_t pagesize = 0;
-
-  ElfW(auxv_t) *av;
-  for (av = auxv;
-       av_entry == NULL || av_phdr == NULL || av_phnum == NULL || pagesize == 0;
-       ++av) {
-    switch (av->a_type) {
-      case AT_NULL:
-        fail("Failed to find AT_ENTRY, AT_PHDR, AT_PHNUM, or AT_PAGESZ!",
-             NULL, 0, NULL, 0);
-        /*NOTREACHED*/
-        break;
-      case AT_ENTRY:
-        av_entry = av;
-        break;
-      case AT_PAGESZ:
-        pagesize = av->a_un.a_val;
-        break;
-      case AT_PHDR:
-        av_phdr = av;
-        break;
-      case AT_PHNUM:
-        av_phnum = av;
-        break;
-    }
-  }
-
-  int fd = my_open(DYNAMIC_LINKER, O_RDONLY);
-
-  ElfW(Ehdr) ehdr;
-  my_pread("Failed to read ELF header from dynamic linker!  ",
-           fd, &ehdr, sizeof(ehdr), 0);
-
-  if (ehdr.e_ident[EI_MAG0] != ELFMAG0 ||
-      ehdr.e_ident[EI_MAG1] != ELFMAG1 ||
-      ehdr.e_ident[EI_MAG2] != ELFMAG2 ||
-      ehdr.e_ident[EI_MAG3] != ELFMAG3 ||
-      ehdr.e_version != EV_CURRENT ||
-      ehdr.e_ehsize != sizeof(ehdr) ||
-      ehdr.e_phentsize != sizeof(ElfW(Phdr)))
-    fail("Dynamic linker has no valid ELF header!", NULL, 0, NULL, 0);
-
-  switch (ehdr.e_machine) {
-#if defined(__i386__)
-    case EM_386:
-#elif defined(__x86_64__)
-    case EM_X86_64:
-#elif defined(__arm__)
-    case EM_ARM:
-#else
-# error "Don't know the e_machine value for this architecture!"
-#endif
-      break;
-    default:
-      fail("Dynamic linker has wrong architecture!  ",
-           "e_machine", ehdr.e_machine, NULL, 0);
-      break;
-  }
-
-  ElfW(Phdr) phdr[MAX_PHNUM];
-  if (ehdr.e_phnum > sizeof(phdr) / sizeof(phdr[0]) || ehdr.e_phnum < 1)
-    fail("Dynamic linker has unreasonable ",
-         "e_phnum", ehdr.e_phnum, NULL, 0);
-
-  if (ehdr.e_type != ET_DYN)
-    fail("Dynamic linker not ET_DYN!  ",
-         "e_type", ehdr.e_type, NULL, 0);
-
-  my_pread("Failed to read program headers from dynamic linker!  ",
-           fd, phdr, sizeof(phdr[0]) * ehdr.e_phnum, ehdr.e_phoff);
-
-  size_t i = 0;
-  while (i < ehdr.e_phnum && phdr[i].p_type != PT_LOAD)
-    ++i;
-  if (i == ehdr.e_phnum)
-    fail("Dynamic linker has no PT_LOAD header!",
-         NULL, 0, NULL, 0);
-
-  /*
-   * ELF requires that PT_LOAD segments be in ascending order of p_vaddr.
-   * Find the last one to calculate the whole address span of the image.
-   */
-  const ElfW(Phdr) *first_load = &phdr[i];
-  const ElfW(Phdr) *last_load = &phdr[ehdr.e_phnum - 1];
-  while (last_load > first_load && last_load->p_type != PT_LOAD)
-    --last_load;
-
-  size_t span = last_load->p_vaddr + last_load->p_memsz - first_load->p_vaddr;
-
-  /*
-   * Map the first segment and reserve the space used for the rest and
-   * for holes between segments.
-   */
-  const uintptr_t mapping = my_mmap("segment", first_load - phdr,
-                                    round_down(first_load->p_vaddr, pagesize),
-                                    span, prot_from_phdr(first_load),
-                                    MAP_PRIVATE, fd,
-                                    round_down(first_load->p_offset, pagesize));
-
-  const ElfW(Addr) load_bias = mapping - round_down(first_load->p_vaddr,
-                                                    pagesize);
-
-  if (first_load->p_offset > ehdr.e_phoff ||
-      first_load->p_filesz < ehdr.e_phoff + (ehdr.e_phnum * sizeof(ElfW(Phdr))))
-    fail("First load segment of dynamic linker does not contain phdrs!",
-         NULL, 0, NULL, 0);
-
-  /* Point the auxv elements at the dynamic linker's phdrs and entry.  */
-  av_phdr->a_un.a_val = (ehdr.e_phoff - first_load->p_offset +
-                         first_load->p_vaddr + load_bias);
-  av_phnum->a_un.a_val = ehdr.e_phnum;
-  av_entry->a_un.a_val = ehdr.e_entry + load_bias;
-
-  handle_bss(first_load - phdr, first_load, load_bias, pagesize);
-
-  ElfW(Addr) last_end = first_load->p_vaddr + load_bias + first_load->p_memsz;
-
-  /*
-   * Map the remaining segments, and protect any holes between them.
-   */
-  const ElfW(Phdr) *ph;
-  for (ph = first_load + 1; ph <= last_load; ++ph) {
-    if (ph->p_type == PT_LOAD) {
-      ElfW(Addr) last_page_end = round_up(last_end, pagesize);
-
-      last_end = ph->p_vaddr + load_bias + ph->p_memsz;
-      ElfW(Addr) start = round_down(ph->p_vaddr + load_bias, pagesize);
-      ElfW(Addr) end = round_up(last_end, pagesize);
-
-      if (start > last_page_end)
-        my_mprotect(ph - phdr, last_page_end, start - last_page_end, PROT_NONE);
-
-      my_mmap("segment", ph - phdr,
-              start, end - start,
-              prot_from_phdr(ph), MAP_PRIVATE | MAP_FIXED, fd,
-              round_down(ph->p_offset, pagesize));
-
-      handle_bss(ph - phdr, ph, load_bias, pagesize);
-    }
-  }
-
-  sys_close(fd);
-
-  return ehdr.e_entry + load_bias;
-}
-
-/*
- * We have to define the actual entry point code (_start) in assembly
- * for each machine.  The kernel startup protocol is not compatible
- * with the normal C function calling convention.  Here, we calculate
- * the address of the auxiliary vector on the stack; call do_load
- * (above) using the normal C convention as per the ABI; restore the
- * original starting stack; and finally, jump to the dynamic linker's
- * entry point address.
- */
-#if defined(__i386__)
-asm(".globl _start\n"
-    ".type _start,@function\n"
-    "_start:\n"
-    "xorl %ebp, %ebp\n"
-    "movl %esp, %ebx\n"         /* Save starting SP in %ebx.  */
-    "andl $-16, %esp\n"         /* Align the stack as per ABI.  */
-    "movl (%ebx), %eax\n"       /* argc */
-    "leal 8(%ebx,%eax,4), %ecx\n" /* envp */
-    /* Find the envp element that is NULL, and auxv is past there.  */
-    "0: addl $4, %ecx\n"
-    "cmpl $0, -4(%ecx)\n"
-    "jne 0b\n"
-    "pushl %ecx\n"              /* Argument: auxv.  */
-    "call do_load\n"
-    "movl %ebx, %esp\n"         /* Restore the saved SP.  */
-    "jmp *%eax\n"               /* Jump to the entry point.  */
-    );
-#elif defined(__x86_64__)
-asm(".globl _start\n"
-    ".type _start,@function\n"
-    "_start:\n"
-    "xorq %rbp, %rbp\n"
-    "movq %rsp, %rbx\n"         /* Save starting SP in %rbx.  */
-    "andq $-16, %rsp\n"         /* Align the stack as per ABI.  */
-    "movq (%rbx), %rax\n"       /* argc */
-    "leaq 16(%rbx,%rax,8), %rdi\n"  /* envp */
-    /* Find the envp element that is NULL, and auxv is past there.  */
-    "0: addq $8, %rdi\n"
-    "cmpq $0, -8(%rdi)\n"
-    "jne 0b\n"
-    "call do_load\n"            /* Argument already in %rdi: auxv */
-    "movq %rbx, %rsp\n"         /* Restore the saved SP.  */
-    "jmp *%rax\n"               /* Jump to the entry point.  */
-    );
-#elif defined(__arm__)
-asm(".globl _start\n"
-    ".type _start,#function\n"
-    "_start:\n"
-#if defined(__thumb2__)
-    ".thumb\n"
-    ".syntax unified\n"
-#endif
-    "mov fp, #0\n"
-    "mov lr, #0\n"
-    "mov r4, sp\n"              /* Save starting SP in r4.  */
-    "ldr r1, [r4]\n"            /* argc */
-    "add r1, r1, #2\n"
-    "add r0, r4, r1, asl #2\n"  /* envp */
-    /* Find the envp element that is NULL, and auxv is past there.  */
-    "0: ldr r1, [r0], #4\n"
-    "cmp r1, #0\n"
-    "bne 0b\n"
-    "bl do_load\n"
-    "mov sp, r4\n"              /* Restore the saved SP.  */
-    "blx r0\n"                  /* Jump to the entry point.  */
-    );
-#else
-# error "Need stack-preserving _start code for this architecture!"
-#endif