Adds tls_edit utility which patches irt_core.nexe's TLS usage.

src/untrusted/irt/tls_edit.c

+/*
+ * Copyright (c) 2014 The Native Client 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 alters instructions for the IRT so that access to the TLS
+ * point to the IRT's TLS.
+ */
+
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#include "native_client/src/include/elf32.h"
+#include "native_client/src/include/elf64.h"
+#include "native_client/src/include/arm_sandbox.h"
+#include "native_client/src/include/portability.h"
+#include "native_client/src/trusted/validator_ragel/validator.h"
+
+#ifndef O_BINARY
+# define O_BINARY 0

[Roland McGrath, 2014/02/03 21:25:14]

This is unused since you switched to stdio.  Drop it.
Probably can also drop #include <fcntl.h>.

+#endif
+
+static void *g_contents;
+static size_t g_contents_size;
+static uint8_t *g_code_start;
+static uint32_t g_code_addr;
+static int g_errors;
+static int g_changes;
+
+static uint32_t GetInsnAddr(const void *insn) {
+  return (uint32_t) ((uint8_t *) insn - g_code_start) + g_code_addr;
+}
+
+static void ReportError(const void *insn, const char *message) {
+  uint32_t insn_addr = GetInsnAddr(insn);
+
+  fprintf(stderr, "%#x: %s\n", (unsigned int) insn_addr, message);
+  ++g_errors;
+}
+
+static void EditArmCode(void *code, size_t code_length) {
+  Elf32_Word *const words = code;
+  Elf32_Word *const end = (void *) ((uint8_t *) code + code_length);
+  Elf32_Word *insn;
+
+  for (insn = words; insn < end; ++insn) {
+    if (*insn == NACL_INSTR_ARM_LITERAL_POOL_HEAD) {
+      if ((insn - words) % 4 != 0) {
+        ReportError(insn, "Roadblock not at start of bundle");
+      } else {
+        /*
+         * Ignore the rest of this bundle.
+         */
+        insn += 3;
+      }
+    } else if ((*insn & 0x0FFF0FFF) == 0x05990000) {
+      /*
+       * This is 'ldr REG, [r9, #0]'.
+       * Turn it into 'ldr REG, [r9, #4]'.
+       */
+      *insn |= 4;
+      ++g_changes;
+    }
+  }
+}
+
+static Bool ConsiderOneInsn(const uint8_t *insn_begin, const uint8_t *insn_end,
+                            uint32_t validation_info, void *data) {
+  UNREFERENCED_PARAMETER(data);
+  if (insn_begin[0] == 0x65) {  /* GS prefix */
+    if (insn_end - insn_begin < 6) {
+      ReportError(insn_begin, "Unexpected GS prefix");
+    } else if (insn_end[-1] == 0 && insn_end[-2] == 0 &&
+               insn_end[-3] == 0 && insn_end[-4] == 0) {
+      /*
+       * This is 'something %gs:0'.
+       * Turn it into 'something %gs:4'.
+       */
+       ((uint8_t *) insn_end)[-4] = 4;
+      ++g_changes;
+    } else if (insn_end[-1] == 0 && insn_end[-2] == 0 &&
+               insn_end[-3] == 0 && insn_end[-4] == 4) {
+      /*
+       * The Instruction is already offset to the right location.
+       * TODO: This case should be removed eventually once the IRT
+       * is being properly compiled without any special TLS flags.
+       */
+      uint32_t insn_addr = GetInsnAddr(insn_begin);
+      printf("%#x: %%gs address already pointing to correct offset (4)\n",
+             insn_addr);
+    } else {
+      ReportError(insn_begin, "Unexpected %gs address");
+    }
+  }
+  return (validation_info & (VALIDATION_ERRORS_MASK | BAD_JUMP_TARGET)) == 0;
+}
+
+static void EditX86_32Code(void *code, size_t code_length) {
+  const NaClCPUFeaturesX86 *cpu_features = &kFullCPUIDFeatures;
+  if (!ValidateChunkIA32(code, code_length,
+                         CALL_USER_CALLBACK_ON_EACH_INSTRUCTION,
+                         cpu_features, &ConsiderOneInsn, NULL))
+    ReportError(code, "Validation failed");
+}
+
+static void ReadInput(const char *filename) {
+  struct stat st;
+  FILE *fp = fopen(filename, "rb");
+  if (fp == NULL) {
+    fprintf(stderr, "fopen: %s: %s\n",
+            filename, strerror(errno));
+    exit(1);
+  }
+
+  if (fstat(fileno(fp), &st) < 0) {
+    fprintf(stderr, "fstat: %s: %s\n",
+            filename, strerror(errno));
+    exit(1);
+  }
+
+  g_contents_size = st.st_size;
+  g_contents = malloc(g_contents_size);
+  if (g_contents == NULL) {
+    fprintf(stderr, "Cannot allocate %u bytes: %s\n",
+            (unsigned int) st.st_size, strerror(errno));
+    exit(1);
+  }
+
+  {
+    size_t read_bytes = fread(g_contents, 1, g_contents_size, fp);
+    if (read_bytes != g_contents_size) {
+      if (ferror(fp)) {
+        fprintf(stderr, "fread: %s: %s\n",
+                filename, strerror(errno));
+      } else if (feof(fp)) {
+        fprintf(stderr, "fread: %s: premature EOF\n",
+                filename);
+      } else {
+        fprintf(stderr, "fread: %s: unexpected read count - %u != %u\n",
+                filename, (unsigned int) read_bytes,
+                (unsigned int) g_contents_size);
+      }
+      exit(1);
+    }
+  }
+
+  fclose(fp);
+}
+
+static void WriteOutput(const char *filename) {
+  FILE *fp = fopen(filename, "wb+");
+  if (fp == NULL) {
+    fprintf(stderr, "fopen: %s: %s\n", filename, strerror(errno));
+    exit(1);
+  }
+
+  {
+    size_t nwrote = fwrite(g_contents, 1, g_contents_size, fp);
+    if (nwrote != g_contents_size) {
+      fprintf(stderr, "fwrite: %s: %s\n", filename, strerror(errno));
+      exit(1);
+    }
+  }
+
+  fclose(fp);
+}
+
+static Bool EditTLSCode(const char *infile, uint32_t code_addr,
+                        uint8_t *code_start, size_t code_length,
+                        uint16_t e_machine) {
+  g_code_addr = code_addr;
+  g_code_start = code_start;
+
+  switch (e_machine) {
+    case EM_ARM:
+      EditArmCode(g_code_start, code_length);
+      break;
+    case EM_386:
+      EditX86_32Code(g_code_start, code_length);
+      break;
+    case EM_X86_64:
+      printf("%s: x86-64 ELF detected, no instructions changed\n",
+             infile);
+      return TRUE;
+    default:

[Mark Seaborn, 2014/02/03 22:31:47]

Can you make tls_edit a no-op on MIPS so that this doesn't break the MIPS build?

+      fprintf(stderr, "%s: Unsupported e_machine %d\n",
+              infile, e_machine);
+      return FALSE;
+  }
+
+  /*
+   * TODO: Until we dep roll native_client changes, no instructions

[Mark Seaborn, 2014/02/03 22:31:47]

Nit: TODOs should have a name, i.e. "TODO(dyen):".

+   * should be changed. No changes to make should return FALSE eventually.

[Mark Seaborn, 2014/02/03 22:31:47]

FWIW, that's not necessarily true if you happen to have a trivial IRT
implementation (e.g. for testing) that happens not to use TLS at all.

+   */
+  if (g_changes == 0) {
+    fprintf(stderr, "%s: Found no changes to make\n",
+            infile);
+    return TRUE;
+  } else {
+    printf("%s: %d instructions changed\n",
+           infile, g_changes);
+  }
+
+  return TRUE;
+}
+
+static Bool Process32BitFile(const char *infile) {
+  const Elf32_Ehdr *ehdr;
+  const Elf32_Phdr *phdr;
+  int i;
+
+  ehdr = g_contents;
+  if (ehdr->e_phoff > g_contents_size) {
+    fprintf(stderr, "%s: bogus e_phoff\n",
+            infile);
+    return FALSE;
+  }
+  if (ehdr->e_ident[EI_CLASS] != ELFCLASS32) {
+    fprintf(stderr, "%s: not an ELFCLASS32 file\n",
+            infile);
+    return FALSE;
+  }
+  if (ehdr->e_phentsize != sizeof(Elf32_Phdr)) {
+    fprintf(stderr, "%s: wrong e_phentsize: %u\n",
+            infile, ehdr->e_phentsize);
+    return FALSE;
+  }
+  if (g_contents_size - ehdr->e_phoff < ehdr->e_phnum * sizeof(Elf32_Phdr)) {
+    fprintf(stderr, "%s: bogus elf32 e_phnum\n",
+            infile);
+    return FALSE;
+  }
+
+  if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB) {
+    fprintf(stderr, "%s: not an ELFDATA2LSB file\n",
+            infile);
+    return FALSE;
+  }
+
+  phdr = (const void *) ((uint8_t *) g_contents + ehdr->e_phoff);
+  for (i = 0; i < ehdr->e_phnum; ++i) {
+    if (phdr[i].p_type == PT_LOAD && (phdr[i].p_flags & PF_X) != 0)
+      break;
+    }
+  if (i == ehdr->e_phnum) {
+    fprintf(stderr, "%s: Could not find executable load segment!\n",
+            infile);
+    return FALSE;
+  }
+
+  if (phdr[i].p_offset > g_contents_size ||
+      g_contents_size - phdr[i].p_offset < phdr[i].p_filesz) {
+    fprintf(stderr, "%s: Program header %d has invalid offset or size!\n",
+            infile, i);
+    return FALSE;
+  }
+
+  return EditTLSCode(infile, phdr[i].p_vaddr,
+                     (uint8_t *) g_contents + phdr[i].p_offset,
+                     phdr[i].p_filesz, ehdr->e_machine);
+}
+
+static Bool Process64BitFile(const char *infile) {
+  const Elf64_Ehdr *ehdr;
+  const Elf64_Phdr *phdr;
+  int i;
+
+  ehdr = g_contents;
+  if (ehdr->e_phoff > g_contents_size) {
+    fprintf(stderr, "%s: bogus e_phoff\n",
+            infile);
+    return FALSE;
+  }
+  if (ehdr->e_ident[EI_CLASS] != ELFCLASS64) {
+    fprintf(stderr, "%s: not an ELFCLASS64 file\n",
+            infile);
+    return FALSE;
+  }
+  if (ehdr->e_phentsize != sizeof(Elf64_Phdr)) {
+    fprintf(stderr, "%s: wrong e_phentsize: %u\n",
+            infile, ehdr->e_phentsize);
+    return FALSE;
+  }
+  if (g_contents_size - ehdr->e_phoff < ehdr->e_phnum * sizeof(Elf64_Phdr)) {
+    fprintf(stderr, "%s: bogus elf64 e_phnum\n",
+            infile);
+    return FALSE;
+  }
+
+  if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB) {
+    fprintf(stderr, "%s: not an ELFDATA2LSB file\n",
+            infile);
+    return FALSE;
+  }
+
+  phdr = (const void *) ((uint8_t *) g_contents + ehdr->e_phoff);
+  for (i = 0; i < ehdr->e_phnum; ++i) {
+    if (phdr[i].p_type == PT_LOAD && (phdr[i].p_flags & PF_X) != 0)
+      break;
+    }
+  if (i == ehdr->e_phnum) {
+    fprintf(stderr, "%s: Could not find executable load segment!\n",
+            infile);
+    return FALSE;
+  }
+
+  if (phdr[i].p_offset > g_contents_size ||
+      g_contents_size - phdr[i].p_offset < phdr[i].p_filesz) {
+    fprintf(stderr, "%s: Program header %d has invalid offset or size!\n",
+            infile, i);
+    return FALSE;
+  }
+
+  return EditTLSCode(infile, (uint32_t) phdr[i].p_vaddr,
+                     (uint8_t *) g_contents + phdr[i].p_offset,
+                     (size_t) phdr[i].p_filesz, ehdr->e_machine);
+}
+
+int main(int argc, char **argv) {
+  const char *infile;
+  const char *outfile;
+
+  if (argc != 3) {
+    fprintf(stderr, "Usage: %s INFILE OUTFILE\n", argv[0]);
+    return 1;
+  }
+
+  infile = argv[1];
+  outfile = argv[2];
+
+  ReadInput(infile);
+
+  if (g_contents_size < SELFMAG) {
+    fprintf(stderr, "%s: too short to be an ELF file\n",
+            infile);
+    return 1;
+  }
+  if (memcmp(g_contents, ELFMAG, SELFMAG) != 0) {
+    fprintf(stderr, "%s: not an ELF file\n",
+            infile);
+    return 1;
+  }
+
+  /*
+  * We will examine the header to figure out whether we are dealing
+  * with a 32 bit or 64 bit executable file.
+  */
+  if (g_contents_size >= sizeof(Elf32_Ehdr) &&
+      ((Elf32_Ehdr*) g_contents)->e_ident[EI_CLASS] == ELFCLASS32) {
+    if (!Process32BitFile(infile)) {
+      fprintf(stderr, "%s: Could not process 32 bit ELF file\n",
+              infile);
+      return 1;
+    }
+  } else if (g_contents_size >= sizeof(Elf64_Ehdr) &&
+             ((Elf64_Ehdr*) g_contents)->e_ident[EI_CLASS] == ELFCLASS64) {
+    if (!Process64BitFile(infile)) {
+      fprintf(stderr, "%s: Could not process 64 bit ELF file\n",
+              infile);
+      return 1;
+    }
+  } else {
+    fprintf(stderr, "%s: Invalid ELF file!\n",
+            infile);
+    return 1;
+  }
+
+  if (g_errors != 0)
+    return 1;
+
+  WriteOutput(outfile);
+  return 0;
+}