forked from mirrors/gecko-dev
e226046cb8
# ignore-this-changeset Depends on D28954 Differential Revision: https://phabricator.services.mozilla.com/D28956 --HG-- extra : moz-landing-system : lando
124 lines
4.8 KiB
C
124 lines
4.8 KiB
C
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include <stdint.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/mman.h>
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#include <elf.h>
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/* The Android NDK headers define those */
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#undef Elf_Ehdr
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#undef Elf_Addr
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#if defined(__LP64__)
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# define Elf_Ehdr Elf64_Ehdr
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# define Elf_Addr Elf64_Addr
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#else
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# define Elf_Ehdr Elf32_Ehdr
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# define Elf_Addr Elf32_Addr
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#endif
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// On ARM, PC-relative function calls have a limit in how far they can jump,
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// which might not be enough for e.g. libxul.so. The easy way out would be
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// to use the long_call attribute, which forces the compiler to generate code
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// that can call anywhere, but clang doesn't support the attribute yet
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// (https://bugs.llvm.org/show_bug.cgi?id=40623), and while the command-line
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// equivalent does exist, it's currently broken
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// (https://bugs.llvm.org/show_bug.cgi?id=40624). So we create a manual
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// trampoline, corresponding to the code GCC generates with long_call.
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#ifdef __arm__
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__attribute__((section(".text._init_trampoline"), naked)) int init_trampoline(
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int argc, char** argv, char** env) {
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__asm__ __volatile__(
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// thumb doesn't allow to use r12/ip with ldr, and thus would require an
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// additional push/pop to save/restore the modified register, which would
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// also change the call into a blx. It's simpler to switch to arm.
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".arm\n"
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" ldr ip, .LADDR\n"
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".LAFTER:\n"
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" add ip, pc, ip\n"
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" bx ip\n"
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".LADDR:\n"
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" .word real_original_init-(.LAFTER+8)\n");
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}
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#endif
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extern __attribute__((visibility("hidden"))) void original_init(int argc,
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char** argv,
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char** env);
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extern __attribute__((visibility("hidden"))) Elf32_Rel relhack[];
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extern __attribute__((visibility("hidden"))) Elf_Ehdr elf_header;
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extern __attribute__((visibility("hidden"))) int (*mprotect_cb)(void* addr,
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size_t len,
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int prot);
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extern __attribute__((visibility("hidden"))) long (*sysconf_cb)(int name);
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extern __attribute__((visibility("hidden"))) char relro_start[];
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extern __attribute__((visibility("hidden"))) char relro_end[];
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static inline __attribute__((always_inline)) void do_relocations(void) {
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Elf32_Rel* rel;
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Elf_Addr *ptr, *start;
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for (rel = relhack; rel->r_offset; rel++) {
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start = (Elf_Addr*)((intptr_t)&elf_header + rel->r_offset);
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for (ptr = start; ptr < &start[rel->r_info]; ptr++)
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*ptr += (intptr_t)&elf_header;
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}
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}
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__attribute__((section(".text._init_noinit"))) int init_noinit(int argc,
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char** argv,
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char** env) {
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do_relocations();
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return 0;
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}
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__attribute__((section(".text._init"))) int init(int argc, char** argv,
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char** env) {
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do_relocations();
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original_init(argc, argv, env);
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// Ensure there is no tail-call optimization, avoiding the use of the
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// B.W instruction in Thumb for the call above.
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return 0;
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}
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static inline __attribute__((always_inline)) void do_relocations_with_relro(
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void) {
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long page_size = sysconf_cb(_SC_PAGESIZE);
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uintptr_t aligned_relro_start = ((uintptr_t)relro_start) & ~(page_size - 1);
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// The relro segment may not end at a page boundary. If that's the case, the
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// remainder of the page needs to stay read-write, so the last page is never
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// set read-only. Thus the aligned relro end is page-rounded down.
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uintptr_t aligned_relro_end = ((uintptr_t)relro_end) & ~(page_size - 1);
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// By the time the injected code runs, the relro segment is read-only. But
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// we want to apply relocations in it, so we set it r/w first. We'll restore
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// it to read-only in relro_post.
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mprotect_cb((void*)aligned_relro_start,
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aligned_relro_end - aligned_relro_start, PROT_READ | PROT_WRITE);
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do_relocations();
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mprotect_cb((void*)aligned_relro_start,
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aligned_relro_end - aligned_relro_start, PROT_READ);
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// mprotect_cb and sysconf_cb are allocated in .bss, so we need to restore
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// them to a NULL value.
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mprotect_cb = NULL;
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sysconf_cb = NULL;
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}
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__attribute__((section(".text._init_noinit_relro"))) int init_noinit_relro(
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int argc, char** argv, char** env) {
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do_relocations_with_relro();
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return 0;
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}
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__attribute__((section(".text._init_relro"))) int init_relro(int argc,
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char** argv,
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char** env) {
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do_relocations_with_relro();
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original_init(argc, argv, env);
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return 0;
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}
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