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// Copyright 2017 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 file contains all the logic necessary to intercept allocations on
// macOS. "malloc zones" are an abstraction that allows the process to intercept
// all malloc-related functions. There is no good mechanism [short of
// interposition] to determine new malloc zones are added, so there's no clean
// mechanism to intercept all malloc zones. This file contains logic to
// intercept the default and purgeable zones, which always exist. A cursory
// review of Chrome seems to imply that non-default zones are almost never used.
//
// This file also contains logic to intercept Core Foundation and Objective-C
// allocations. The implementations forward to the default malloc zone, so the
// only reason to intercept these calls is to re-label OOM crashes with slightly
// more details.
#include "base/allocator/allocator_interception_mac.h"
#include <CoreFoundation/CoreFoundation.h>
#import <Foundation/Foundation.h>
#include <errno.h>
#include <mach/mach.h>
#include <mach/mach_vm.h>
#import <objc/runtime.h>
#include <stddef.h>
#include <new>
#include "base/allocator/allocator_shim.h"
#include "base/allocator/features.h"
#include "base/allocator/malloc_zone_functions_mac.h"
#include "base/logging.h"
#include "base/mac/mac_util.h"
#include "base/mac/mach_logging.h"
#include "base/process/memory.h"
#include "base/scoped_clear_errno.h"
#include "build/build_config.h"
#include "third_party/apple_apsl/CFBase.h"
namespace base {
namespace allocator {
bool g_replaced_default_zone = false;
namespace {
bool g_oom_killer_enabled;
// Starting with Mac OS X 10.7, the zone allocators set up by the system are
// read-only, to prevent them from being overwritten in an attack. However,
// blindly unprotecting and reprotecting the zone allocators fails with
// GuardMalloc because GuardMalloc sets up its zone allocator using a block of
// memory in its bss. Explicit saving/restoring of the protection is required.
//
// This function takes a pointer to a malloc zone, de-protects it if necessary,
// and returns (in the out parameters) a region of memory (if any) to be
// re-protected when modifications are complete. This approach assumes that
// there is no contention for the protection of this memory.
void DeprotectMallocZone(ChromeMallocZone* default_zone,
mach_vm_address_t* reprotection_start,
mach_vm_size_t* reprotection_length,
vm_prot_t* reprotection_value) {
mach_port_t unused;
*reprotection_start = reinterpret_cast<mach_vm_address_t>(default_zone);
struct vm_region_basic_info_64 info;
mach_msg_type_number_t count = VM_REGION_BASIC_INFO_COUNT_64;
kern_return_t result = mach_vm_region(
mach_task_self(), reprotection_start, reprotection_length,
VM_REGION_BASIC_INFO_64, reinterpret_cast<vm_region_info_t>(&info),
&count, &unused);
MACH_CHECK(result == KERN_SUCCESS, result) << "mach_vm_region";
// The kernel always returns a null object for VM_REGION_BASIC_INFO_64, but
// balance it with a deallocate in case this ever changes. See 10.9.2
// xnu-2422.90.20/osfmk/vm/vm_map.c vm_map_region.
mach_port_deallocate(mach_task_self(), unused);
// Does the region fully enclose the zone pointers? Possibly unwarranted
// simplification used: using the size of a full version 8 malloc zone rather
// than the actual smaller size if the passed-in zone is not version 8.
CHECK(*reprotection_start <=
reinterpret_cast<mach_vm_address_t>(default_zone));
mach_vm_size_t zone_offset =
reinterpret_cast<mach_vm_size_t>(default_zone) -
reinterpret_cast<mach_vm_size_t>(*reprotection_start);
CHECK(zone_offset + sizeof(ChromeMallocZone) <= *reprotection_length);
if (info.protection & VM_PROT_WRITE) {
// No change needed; the zone is already writable.
*reprotection_start = 0;
*reprotection_length = 0;
*reprotection_value = VM_PROT_NONE;
} else {
*reprotection_value = info.protection;
result = mach_vm_protect(mach_task_self(), *reprotection_start,
*reprotection_length, false,
info.protection | VM_PROT_WRITE);
MACH_CHECK(result == KERN_SUCCESS, result) << "mach_vm_protect";
}
}
#if !defined(ADDRESS_SANITIZER)
MallocZoneFunctions g_old_zone;
MallocZoneFunctions g_old_purgeable_zone;
void* oom_killer_malloc(struct _malloc_zone_t* zone, size_t size) {
void* result = g_old_zone.malloc(zone, size);
if (!result && size)
TerminateBecauseOutOfMemory(size);
return result;
}
void* oom_killer_calloc(struct _malloc_zone_t* zone,
size_t num_items,
size_t size) {
void* result = g_old_zone.calloc(zone, num_items, size);
if (!result && num_items && size)
TerminateBecauseOutOfMemory(num_items * size);
return result;
}
void* oom_killer_valloc(struct _malloc_zone_t* zone, size_t size) {
void* result = g_old_zone.valloc(zone, size);
if (!result && size)
TerminateBecauseOutOfMemory(size);
return result;
}
void oom_killer_free(struct _malloc_zone_t* zone, void* ptr) {
g_old_zone.free(zone, ptr);
}
void* oom_killer_realloc(struct _malloc_zone_t* zone, void* ptr, size_t size) {
void* result = g_old_zone.realloc(zone, ptr, size);
if (!result && size)
TerminateBecauseOutOfMemory(size);
return result;
}
void* oom_killer_memalign(struct _malloc_zone_t* zone,
size_t alignment,
size_t size) {
void* result = g_old_zone.memalign(zone, alignment, size);
// Only die if posix_memalign would have returned ENOMEM, since there are
// other reasons why NULL might be returned (see
// http://opensource.apple.com/source/Libc/Libc-583/gen/malloc.c ).
if (!result && size && alignment >= sizeof(void*) &&
(alignment & (alignment - 1)) == 0) {
TerminateBecauseOutOfMemory(size);
}
return result;
}
void* oom_killer_malloc_purgeable(struct _malloc_zone_t* zone, size_t size) {
void* result = g_old_purgeable_zone.malloc(zone, size);
if (!result && size)
TerminateBecauseOutOfMemory(size);
return result;
}
void* oom_killer_calloc_purgeable(struct _malloc_zone_t* zone,
size_t num_items,
size_t size) {
void* result = g_old_purgeable_zone.calloc(zone, num_items, size);
if (!result && num_items && size)
TerminateBecauseOutOfMemory(num_items * size);
return result;
}
void* oom_killer_valloc_purgeable(struct _malloc_zone_t* zone, size_t size) {
void* result = g_old_purgeable_zone.valloc(zone, size);
if (!result && size)
TerminateBecauseOutOfMemory(size);
return result;
}
void oom_killer_free_purgeable(struct _malloc_zone_t* zone, void* ptr) {
g_old_purgeable_zone.free(zone, ptr);
}
void* oom_killer_realloc_purgeable(struct _malloc_zone_t* zone,
void* ptr,
size_t size) {
void* result = g_old_purgeable_zone.realloc(zone, ptr, size);
if (!result && size)
TerminateBecauseOutOfMemory(size);
return result;
}
void* oom_killer_memalign_purgeable(struct _malloc_zone_t* zone,
size_t alignment,
size_t size) {
void* result = g_old_purgeable_zone.memalign(zone, alignment, size);
// Only die if posix_memalign would have returned ENOMEM, since there are
// other reasons why NULL might be returned (see
// http://opensource.apple.com/source/Libc/Libc-583/gen/malloc.c ).
if (!result && size && alignment >= sizeof(void*) &&
(alignment & (alignment - 1)) == 0) {
TerminateBecauseOutOfMemory(size);
}
return result;
}
#endif // !defined(ADDRESS_SANITIZER)
#if !defined(ADDRESS_SANITIZER)
// === Core Foundation CFAllocators ===
bool CanGetContextForCFAllocator() {
return !base::mac::IsOSLaterThan10_12_DontCallThis();
}
CFAllocatorContext* ContextForCFAllocator(CFAllocatorRef allocator) {
ChromeCFAllocatorLions* our_allocator = const_cast<ChromeCFAllocatorLions*>(
reinterpret_cast<const ChromeCFAllocatorLions*>(allocator));
return &our_allocator->_context;
}
CFAllocatorAllocateCallBack g_old_cfallocator_system_default;
CFAllocatorAllocateCallBack g_old_cfallocator_malloc;
CFAllocatorAllocateCallBack g_old_cfallocator_malloc_zone;
void* oom_killer_cfallocator_system_default(CFIndex alloc_size,
CFOptionFlags hint,
void* info) {
void* result = g_old_cfallocator_system_default(alloc_size, hint, info);
if (!result)
TerminateBecauseOutOfMemory(alloc_size);
return result;
}
void* oom_killer_cfallocator_malloc(CFIndex alloc_size,
CFOptionFlags hint,
void* info) {
void* result = g_old_cfallocator_malloc(alloc_size, hint, info);
if (!result)
TerminateBecauseOutOfMemory(alloc_size);
return result;
}
void* oom_killer_cfallocator_malloc_zone(CFIndex alloc_size,
CFOptionFlags hint,
void* info) {
void* result = g_old_cfallocator_malloc_zone(alloc_size, hint, info);
if (!result)
TerminateBecauseOutOfMemory(alloc_size);
return result;
}
#endif // !defined(ADDRESS_SANITIZER)
// === Cocoa NSObject allocation ===
typedef id (*allocWithZone_t)(id, SEL, NSZone*);
allocWithZone_t g_old_allocWithZone;
id oom_killer_allocWithZone(id self, SEL _cmd, NSZone* zone) {
id result = g_old_allocWithZone(self, _cmd, zone);
if (!result)
TerminateBecauseOutOfMemory(0);
return result;
}
} // namespace
bool UncheckedMallocMac(size_t size, void** result) {
#if defined(ADDRESS_SANITIZER)
*result = malloc(size);
#else
if (g_old_zone.malloc) {
*result = g_old_zone.malloc(malloc_default_zone(), size);
} else {
*result = malloc(size);
}
#endif // defined(ADDRESS_SANITIZER)
return *result != NULL;
}
bool UncheckedCallocMac(size_t num_items, size_t size, void** result) {
#if defined(ADDRESS_SANITIZER)
*result = calloc(num_items, size);
#else
if (g_old_zone.calloc) {
*result = g_old_zone.calloc(malloc_default_zone(), num_items, size);
} else {
*result = calloc(num_items, size);
}
#endif // defined(ADDRESS_SANITIZER)
return *result != NULL;
}
void ReplaceZoneFunctions(ChromeMallocZone* zone,
const MallocZoneFunctions* functions) {
// Remove protection.
mach_vm_address_t reprotection_start = 0;
mach_vm_size_t reprotection_length = 0;
vm_prot_t reprotection_value = VM_PROT_NONE;
DeprotectMallocZone(zone, &reprotection_start, &reprotection_length,
&reprotection_value);
CHECK(functions->malloc && functions->calloc && functions->valloc &&
functions->free && functions->realloc);
zone->malloc = functions->malloc;
zone->calloc = functions->calloc;
zone->valloc = functions->valloc;
zone->free = functions->free;
zone->realloc = functions->realloc;
if (functions->batch_malloc)
zone->batch_malloc = functions->batch_malloc;
if (functions->batch_free)
zone->batch_free = functions->batch_free;
if (functions->size)
zone->size = functions->size;
if (zone->version >= 5 && functions->memalign) {
zone->memalign = functions->memalign;
}
if (zone->version >= 6 && functions->free_definite_size) {
zone->free_definite_size = functions->free_definite_size;
}
// Restore protection if it was active.
if (reprotection_start) {
kern_return_t result =
mach_vm_protect(mach_task_self(), reprotection_start,
reprotection_length, false, reprotection_value);
MACH_CHECK(result == KERN_SUCCESS, result) << "mach_vm_protect";
}
}
void StoreFunctionsForDefaultZone() {
ChromeMallocZone* default_zone = reinterpret_cast<ChromeMallocZone*>(
malloc_default_zone());
StoreMallocZone(default_zone);
}
void StoreFunctionsForAllZones() {
// This ensures that the default zone is always at the front of the array,
// which is important for performance.
StoreFunctionsForDefaultZone();
vm_address_t* zones;
unsigned int count;
kern_return_t kr = malloc_get_all_zones(mach_task_self(), 0, &zones, &count);
if (kr != KERN_SUCCESS)
return;
for (unsigned int i = 0; i < count; ++i) {
ChromeMallocZone* zone = reinterpret_cast<ChromeMallocZone*>(zones[i]);
StoreMallocZone(zone);
}
}
void ReplaceFunctionsForStoredZones(const MallocZoneFunctions* functions) {
vm_address_t* zones;
unsigned int count;
kern_return_t kr =
malloc_get_all_zones(mach_task_self(), nullptr, &zones, &count);
if (kr != KERN_SUCCESS)
return;
for (unsigned int i = 0; i < count; ++i) {
ChromeMallocZone* zone = reinterpret_cast<ChromeMallocZone*>(zones[i]);
if (IsMallocZoneAlreadyStored(zone) && zone->malloc != functions->malloc) {
ReplaceZoneFunctions(zone, functions);
}
}
g_replaced_default_zone = true;
}
void InterceptAllocationsMac() {
if (g_oom_killer_enabled)
return;
g_oom_killer_enabled = true;
// === C malloc/calloc/valloc/realloc/posix_memalign ===
// This approach is not perfect, as requests for amounts of memory larger than
// MALLOC_ABSOLUTE_MAX_SIZE (currently SIZE_T_MAX - (2 * PAGE_SIZE)) will
// still fail with a NULL rather than dying (see
// http://opensource.apple.com/source/Libc/Libc-583/gen/malloc.c for details).
// Unfortunately, it's the best we can do. Also note that this does not affect
// allocations from non-default zones.
#if !defined(ADDRESS_SANITIZER)
// Don't do anything special on OOM for the malloc zones replaced by
// AddressSanitizer, as modifying or protecting them may not work correctly.
ChromeMallocZone* default_zone =
reinterpret_cast<ChromeMallocZone*>(malloc_default_zone());
if (!IsMallocZoneAlreadyStored(default_zone)) {
StoreZoneFunctions(default_zone, &g_old_zone);
MallocZoneFunctions new_functions;
new_functions.malloc = oom_killer_malloc;
new_functions.calloc = oom_killer_calloc;
new_functions.valloc = oom_killer_valloc;
new_functions.free = oom_killer_free;
new_functions.realloc = oom_killer_realloc;
new_functions.memalign = oom_killer_memalign;
ReplaceZoneFunctions(default_zone, &new_functions);
g_replaced_default_zone = true;
}
ChromeMallocZone* purgeable_zone =
reinterpret_cast<ChromeMallocZone*>(malloc_default_purgeable_zone());
if (purgeable_zone && !IsMallocZoneAlreadyStored(purgeable_zone)) {
StoreZoneFunctions(purgeable_zone, &g_old_purgeable_zone);
MallocZoneFunctions new_functions;
new_functions.malloc = oom_killer_malloc_purgeable;
new_functions.calloc = oom_killer_calloc_purgeable;
new_functions.valloc = oom_killer_valloc_purgeable;
new_functions.free = oom_killer_free_purgeable;
new_functions.realloc = oom_killer_realloc_purgeable;
new_functions.memalign = oom_killer_memalign_purgeable;
ReplaceZoneFunctions(purgeable_zone, &new_functions);
}
#endif
// === C malloc_zone_batch_malloc ===
// batch_malloc is omitted because the default malloc zone's implementation
// only supports batch_malloc for "tiny" allocations from the free list. It
// will fail for allocations larger than "tiny", and will only allocate as
// many blocks as it's able to from the free list. These factors mean that it
// can return less than the requested memory even in a non-out-of-memory
// situation. There's no good way to detect whether a batch_malloc failure is
// due to these other factors, or due to genuine memory or address space
// exhaustion. The fact that it only allocates space from the "tiny" free list
// means that it's likely that a failure will not be due to memory exhaustion.
// Similarly, these constraints on batch_malloc mean that callers must always
// be expecting to receive less memory than was requested, even in situations
// where memory pressure is not a concern. Finally, the only public interface
// to batch_malloc is malloc_zone_batch_malloc, which is specific to the
// system's malloc implementation. It's unlikely that anyone's even heard of
// it.
#ifndef ADDRESS_SANITIZER
// === Core Foundation CFAllocators ===
// This will not catch allocation done by custom allocators, but will catch
// all allocation done by system-provided ones.
CHECK(!g_old_cfallocator_system_default && !g_old_cfallocator_malloc &&
!g_old_cfallocator_malloc_zone)
<< "Old allocators unexpectedly non-null";
bool cf_allocator_internals_known = CanGetContextForCFAllocator();
if (cf_allocator_internals_known) {
CFAllocatorContext* context =
ContextForCFAllocator(kCFAllocatorSystemDefault);
CHECK(context) << "Failed to get context for kCFAllocatorSystemDefault.";
g_old_cfallocator_system_default = context->allocate;
CHECK(g_old_cfallocator_system_default)
<< "Failed to get kCFAllocatorSystemDefault allocation function.";
context->allocate = oom_killer_cfallocator_system_default;
context = ContextForCFAllocator(kCFAllocatorMalloc);
CHECK(context) << "Failed to get context for kCFAllocatorMalloc.";
g_old_cfallocator_malloc = context->allocate;
CHECK(g_old_cfallocator_malloc)
<< "Failed to get kCFAllocatorMalloc allocation function.";
context->allocate = oom_killer_cfallocator_malloc;
context = ContextForCFAllocator(kCFAllocatorMallocZone);
CHECK(context) << "Failed to get context for kCFAllocatorMallocZone.";
g_old_cfallocator_malloc_zone = context->allocate;
CHECK(g_old_cfallocator_malloc_zone)
<< "Failed to get kCFAllocatorMallocZone allocation function.";
context->allocate = oom_killer_cfallocator_malloc_zone;
} else {
DLOG(WARNING) << "Internals of CFAllocator not known; out-of-memory "
"failures via CFAllocator will not result in termination. "
"http://crbug.com/45650";
}
#endif
// === Cocoa NSObject allocation ===
// Note that both +[NSObject new] and +[NSObject alloc] call through to
// +[NSObject allocWithZone:].
CHECK(!g_old_allocWithZone) << "Old allocator unexpectedly non-null";
Class nsobject_class = [NSObject class];
Method orig_method =
class_getClassMethod(nsobject_class, @selector(allocWithZone:));
g_old_allocWithZone =
reinterpret_cast<allocWithZone_t>(method_getImplementation(orig_method));
CHECK(g_old_allocWithZone)
<< "Failed to get allocWithZone allocation function.";
method_setImplementation(orig_method,
reinterpret_cast<IMP>(oom_killer_allocWithZone));
}
} // namespace allocator
} // namespace base