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-rw-r--r--build/unix/elfhack/inject.c225
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diff --git a/build/unix/elfhack/inject.c b/build/unix/elfhack/inject.c
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+++ b/build/unix/elfhack/inject.c
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <elf.h>
+
+/* The Android NDK headers define those */
+#undef Elf_Ehdr
+#undef Elf_Addr
+
+#if defined(__LP64__)
+# define Elf_Ehdr Elf64_Ehdr
+# define Elf_Phdr Elf64_Phdr
+# define Elf_Addr Elf64_Addr
+# define Elf_Word Elf64_Word
+# define Elf_Dyn Elf64_Dyn
+#else
+# define Elf_Phdr Elf32_Phdr
+# define Elf_Ehdr Elf32_Ehdr
+# define Elf_Addr Elf32_Addr
+# define Elf_Word Elf32_Word
+# define Elf_Dyn Elf32_Dyn
+#endif
+
+#ifdef RELRHACK
+# include "relrhack.h"
+# define mprotect_cb mprotect
+# define sysconf_cb sysconf
+
+#else
+// On ARM, PC-relative function calls have a limit in how far they can jump,
+// which might not be enough for e.g. libxul.so. The easy way out would be
+// to use the long_call attribute, which forces the compiler to generate code
+// that can call anywhere, but clang doesn't support the attribute yet
+// (https://bugs.llvm.org/show_bug.cgi?id=40623), and while the command-line
+// equivalent does exist, it's currently broken
+// (https://bugs.llvm.org/show_bug.cgi?id=40624). So we create a manual
+// trampoline, corresponding to the code GCC generates with long_call.
+# ifdef __arm__
+__attribute__((section(".text._init_trampoline"), naked)) int init_trampoline(
+ int argc, char** argv, char** env) {
+ __asm__ __volatile__(
+ // thumb doesn't allow to use r12/ip with ldr, and thus would require an
+ // additional push/pop to save/restore the modified register, which would
+ // also change the call into a blx. It's simpler to switch to arm.
+ ".arm\n"
+ " ldr ip, .LADDR\n"
+ ".LAFTER:\n"
+ " add ip, pc, ip\n"
+ " bx ip\n"
+ ".LADDR:\n"
+ " .word real_original_init-(.LAFTER+8)\n");
+}
+# endif
+
+// On aarch64, a similar problem exists, but long_call is not an option at all
+// (even GCC doesn't support them on aarch64).
+# ifdef __aarch64__
+__attribute__((section(".text._init_trampoline"), naked)) int init_trampoline(
+ int argc, char** argv, char** env) {
+ __asm__ __volatile__(
+ " adrp x8, .LADDR\n"
+ " add x8, x8, :lo12:.LADDR\n" // adrp + add gives us the full address
+ // for .LADDR
+ " ldr x0, [x8]\n" // Load the address of real_original_init relative to
+ // .LADDR
+ " add x0, x8, x0\n" // Add the address of .LADDR
+ " br x0\n" // Branch to real_original_init
+ ".LADDR:\n"
+ " .xword real_original_init-.LADDR\n");
+}
+# endif
+
+extern __attribute__((visibility("hidden"))) void original_init(int argc,
+ char** argv,
+ char** env);
+
+extern __attribute__((visibility("hidden"))) Elf_Addr relhack[];
+extern __attribute__((visibility("hidden"))) Elf_Addr relhack_end[];
+
+extern __attribute__((visibility("hidden"))) int (*mprotect_cb)(void* addr,
+ size_t len,
+ int prot);
+extern __attribute__((visibility("hidden"))) long (*sysconf_cb)(int name);
+extern __attribute__((visibility("hidden"))) char relro_start[];
+extern __attribute__((visibility("hidden"))) char relro_end[];
+#endif
+
+extern __attribute__((visibility("hidden"))) Elf_Ehdr __ehdr_start;
+
+static inline __attribute__((always_inline)) void do_relocations(
+ Elf_Addr* relhack, Elf_Addr* relhack_end) {
+ Elf_Addr* ptr;
+ for (Elf_Addr* entry = relhack; entry < relhack_end; entry++) {
+ if ((*entry & 1) == 0) {
+ ptr = (Elf_Addr*)((intptr_t)&__ehdr_start + *entry);
+ *ptr += (intptr_t)&__ehdr_start;
+ } else {
+ Elf_Addr bits = *entry;
+ Elf_Addr* end = ptr + 8 * sizeof(Elf_Addr) - 1;
+ do {
+ ptr++;
+ bits >>= 1;
+ if (bits & 1) {
+ *ptr += (intptr_t)&__ehdr_start;
+ }
+ } while (ptr < end);
+ }
+ }
+}
+
+#ifndef RELRHACK
+__attribute__((section(".text._init_noinit"))) int init_noinit(int argc,
+ char** argv,
+ char** env) {
+ do_relocations(relhack, relhack_end);
+ return 0;
+}
+
+__attribute__((section(".text._init"))) int init(int argc, char** argv,
+ char** env) {
+ do_relocations(relhack, relhack_end);
+ original_init(argc, argv, env);
+ // Ensure there is no tail-call optimization, avoiding the use of the
+ // B.W instruction in Thumb for the call above.
+ return 0;
+}
+#endif
+
+static inline __attribute__((always_inline)) void do_relocations_with_relro(
+ Elf_Addr* relhack, Elf_Addr* relhack_end, char* relro_start,
+ char* relro_end) {
+ long page_size = sysconf_cb(_SC_PAGESIZE);
+ uintptr_t aligned_relro_start = ((uintptr_t)relro_start) & ~(page_size - 1);
+ // The relro segment may not end at a page boundary. If that's the case, the
+ // remainder of the page needs to stay read-write, so the last page is never
+ // set read-only. Thus the aligned relro end is page-rounded down.
+ uintptr_t aligned_relro_end = ((uintptr_t)relro_end) & ~(page_size - 1);
+ // By the time the injected code runs, the relro segment is read-only. But
+ // we want to apply relocations in it, so we set it r/w first. We'll restore
+ // it to read-only in relro_post.
+ mprotect_cb((void*)aligned_relro_start,
+ aligned_relro_end - aligned_relro_start, PROT_READ | PROT_WRITE);
+
+ do_relocations(relhack, relhack_end);
+
+ mprotect_cb((void*)aligned_relro_start,
+ aligned_relro_end - aligned_relro_start, PROT_READ);
+#ifndef RELRHACK
+ // mprotect_cb and sysconf_cb are allocated in .bss, so we need to restore
+ // them to a NULL value.
+ mprotect_cb = NULL;
+ sysconf_cb = NULL;
+#endif
+}
+
+#ifndef RELRHACK
+__attribute__((section(".text._init_noinit_relro"))) int init_noinit_relro(
+ int argc, char** argv, char** env) {
+ do_relocations_with_relro(relhack, relhack_end, relro_start, relro_end);
+ return 0;
+}
+
+__attribute__((section(".text._init_relro"))) int init_relro(int argc,
+ char** argv,
+ char** env) {
+ do_relocations_with_relro(relhack, relhack_end, relro_start, relro_end);
+ original_init(argc, argv, env);
+ return 0;
+}
+#else
+
+extern __attribute__((visibility("hidden"))) Elf_Dyn _DYNAMIC[];
+
+static void _relrhack_init(void) {
+ // Get the location of the SHT_RELR data from the PT_DYNAMIC segment.
+ uintptr_t elf_header = (uintptr_t)&__ehdr_start;
+ Elf_Addr* relhack = NULL;
+ Elf_Word size = 0;
+ for (Elf_Dyn* dyn = _DYNAMIC; dyn->d_tag != DT_NULL; dyn++) {
+ if ((dyn->d_tag & ~DT_RELRHACK_BIT) == DT_RELR) {
+ relhack = (Elf_Addr*)(elf_header + dyn->d_un.d_ptr);
+ } else if ((dyn->d_tag & ~DT_RELRHACK_BIT) == DT_RELRSZ) {
+ size = dyn->d_un.d_val;
+ }
+ }
+
+ Elf_Addr* relhack_end = (Elf_Addr*)((uintptr_t)relhack + size);
+
+ // Find the location of the PT_GNU_RELRO segment in the program headers.
+ Elf_Phdr* phdr = (Elf_Phdr*)(elf_header + __ehdr_start.e_phoff);
+ char* relro_start = NULL;
+ char* relro_end = NULL;
+ for (int i = 0; i < __ehdr_start.e_phnum; i++) {
+ if (phdr[i].p_type == PT_GNU_RELRO) {
+ relro_start = (char*)(elf_header + phdr[i].p_vaddr);
+ relro_end = (char*)(relro_start + phdr[i].p_memsz);
+ break;
+ }
+ }
+
+ if (relro_start != relro_end) {
+ do_relocations_with_relro(relhack, relhack_end, relro_start, relro_end);
+ } else {
+ do_relocations(relhack, relhack_end);
+ }
+}
+
+// The Android CRT doesn't contain an init function.
+# ifndef ANDROID
+extern __attribute__((visibility("hidden"))) void _init(int argc, char** argv,
+ char** env);
+# endif
+
+void _relrhack_wrap_init(int argc, char** argv, char** env) {
+ _relrhack_init();
+# ifndef ANDROID
+ _init(argc, argv, env);
+# endif
+}
+#endif
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