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/*
* Copyright (C) 2016 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <sys/mman.h>
#include "private/CFIShadow.h"
__attribute__((__weak__, visibility("default"))) extern "C" void __loader_cfi_fail(
uint64_t CallSiteTypeId, void* Ptr, void* DiagData, void* CallerPc);
// Base address of the CFI shadow. Passed down from the linker in __cfi_init()
// and does not change after that. The contents of the shadow change in
// dlopen/dlclose.
static struct {
uintptr_t v;
char padding[PAGE_SIZE - sizeof(v)];
} shadow_base_storage alignas(PAGE_SIZE);
// __cfi_init is called by the loader as soon as the shadow is mapped. This may happen very early
// during startup, before libdl.so global constructors, and, on i386, even before __libc_sysinfo is
// initialized. This function should not do any system calls.
extern "C" uintptr_t* __cfi_init(uintptr_t shadow_base) {
shadow_base_storage.v = shadow_base;
static_assert(sizeof(shadow_base_storage) == PAGE_SIZE, "");
return &shadow_base_storage.v;
}
// Returns the size of the CFI shadow mapping, or 0 if CFI is not (yet) used in this process.
extern "C" size_t __cfi_shadow_size() {
return shadow_base_storage.v != 0 ? CFIShadow::kShadowSize : 0;
}
static uint16_t shadow_load(void* p) {
uintptr_t addr = reinterpret_cast<uintptr_t>(p);
uintptr_t ofs = CFIShadow::MemToShadowOffset(addr);
if (ofs > CFIShadow::kShadowSize) return CFIShadow::kInvalidShadow;
return *reinterpret_cast<uint16_t*>(shadow_base_storage.v + ofs);
}
static uintptr_t cfi_check_addr(uint16_t v, void* Ptr) {
uintptr_t addr = reinterpret_cast<uintptr_t>(Ptr);
uintptr_t aligned_addr = align_up(addr, CFIShadow::kShadowAlign);
uintptr_t p = aligned_addr - (static_cast<uintptr_t>(v - CFIShadow::kRegularShadowMin)
<< CFIShadow::kCfiCheckGranularity);
#ifdef __arm__
// Assume Thumb encoding. FIXME: force thumb at compile time?
p++;
#endif
return p;
}
static inline void cfi_slowpath_common(uint64_t CallSiteTypeId, void* Ptr, void* DiagData) {
uint16_t v = shadow_load(Ptr);
switch (v) {
case CFIShadow::kInvalidShadow:
__loader_cfi_fail(CallSiteTypeId, Ptr, DiagData, __builtin_return_address(0));
break;
case CFIShadow::kUncheckedShadow:
break;
default:
reinterpret_cast<CFIShadow::CFICheckFn>(cfi_check_addr(v, Ptr))(CallSiteTypeId, Ptr, DiagData);
}
}
extern "C" void __cfi_slowpath(uint64_t CallSiteTypeId, void* Ptr) {
cfi_slowpath_common(CallSiteTypeId, Ptr, nullptr);
}
extern "C" void __cfi_slowpath_diag(uint64_t CallSiteTypeId, void* Ptr, void* DiagData) {
cfi_slowpath_common(CallSiteTypeId, Ptr, DiagData);
}
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