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- // Copyright 2021 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.
- #include "base/stack_canary_linux.h"
- #include <dlfcn.h>
- #include <stdint.h>
- #include <sys/mman.h>
- #include "base/bits.h"
- #include "base/check_op.h"
- #include "base/compiler_specific.h"
- #include "base/logging.h"
- #include "base/memory/page_size.h"
- #include "base/rand_util.h"
- #include "build/build_config.h"
- namespace base {
- #if defined(LIBC_GLIBC)
- #if defined(ARCH_CPU_ARM_FAMILY)
- // On ARM, Glibc uses a global variable (exported) called __stack_chk_guard.
- extern "C" {
- extern uintptr_t __stack_chk_guard;
- }
- #endif // defined(ARCH_CPU_ARM_FAMILY)
- #if !defined(NDEBUG)
- // In debug builds, if we detect stack smashing in old stack frames after
- // changing the canary, it's nice to let someone know that it's because the
- // canary changed and they should prevent their function from using stack
- // canaries.
- static bool g_emit_debug_message = false;
- extern "C" {
- typedef __attribute__((noreturn)) void(GLibcStackChkFailFunction)();
- // This overrides glibc's version of __stack_chk_fail(), which is called when
- // the canary doesn't match.
- __attribute__((visibility("default"), noinline, noreturn)) void
- __stack_chk_fail() {
- if (g_emit_debug_message) {
- RAW_LOG(
- FATAL,
- "Stack smashing detected. The canary was changed during runtime "
- "(see crbug.com/1206626). You may need to mark your function with "
- "the no_stack_protector attribute, or just exit() before stack "
- "smashing occurs. You can also disable this canary-changing feature "
- "by adding --change-stack-guard-on-fork=disable to the command line.");
- }
- // Call the real __stack_chk_fail().
- // Note that dlsym may not be safe to perform since this is called during
- // corruption, but this code purposely only runs in debug builds and in the
- // normal case might provide better debug information.
- GLibcStackChkFailFunction* glibc_stack_chk_fail =
- reinterpret_cast<GLibcStackChkFailFunction*>(
- dlsym(RTLD_NEXT, "__stack_chk_fail"));
- (*glibc_stack_chk_fail)();
- }
- }
- #endif // !defined(NDEBUG)
- void NO_STACK_PROTECTOR ResetStackCanaryIfPossible() {
- uintptr_t canary;
- base::RandBytes(&canary, sizeof(canary));
- // First byte should be the null byte for string functions.
- canary &= ~static_cast<uintptr_t>(0xff);
- // The x86/x64 offsets should work for musl too.
- #if defined(ARCH_CPU_X86_64)
- asm volatile("movq %q0,%%fs:%P1" : : "er"(canary), "i"(0x28));
- #elif defined(ARCH_CPU_X86)
- asm volatile("movl %0,%%gs:%P1" : : "ir"(canary), "i"(0x14));
- #elif defined(ARCH_CPU_ARM_FAMILY)
- // ARM's stack canary is held on a relro page. So, we'll need to make the page
- // writable, change the stack canary, and then make the page ro again.
- // We want to be single-threaded when changing page permissions, since it's
- // reasonable for other threads to assume that page permissions for global
- // variables don't change.
- size_t page_size = base::GetPageSize();
- uintptr_t __stack_chk_guard_page = base::bits::AlignDown(
- reinterpret_cast<uintptr_t>(&__stack_chk_guard), page_size);
- PCHECK(0 == mprotect(reinterpret_cast<void*>(__stack_chk_guard_page),
- page_size, PROT_READ | PROT_WRITE));
- __stack_chk_guard = canary;
- PCHECK(0 == mprotect(reinterpret_cast<void*>(__stack_chk_guard_page),
- page_size, PROT_READ));
- #endif
- }
- void SetStackSmashingEmitsDebugMessage() {
- #if !defined(NDEBUG)
- g_emit_debug_message = true;
- #endif // !defined(NDEBUG)
- }
- #else // defined(LIBC_GLIBC)
- // We don't know how to reset the canary if not compiling for glibc.
- void ResetStackCanaryIfPossible() {}
- void SetStackSmashingEmitsDebugMessage() {}
- #endif // defined(LIBC_GLIBC)
- } // namespace base
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