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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include <sys/mman.h>
     18 
     19 #include "private/CFIShadow.h"
     20 
     21 __attribute__((__weak__, visibility("default"))) extern "C" void __loader_cfi_fail(
     22     uint64_t CallSiteTypeId, void* Ptr, void* DiagData, void* CallerPc);
     23 
     24 // Base address of the CFI shadow. Passed down from the linker in __cfi_init()
     25 // and does not change after that. The contents of the shadow change in
     26 // dlopen/dlclose.
     27 static struct {
     28   uintptr_t v;
     29   char padding[PAGE_SIZE - sizeof(v)];
     30 } shadow_base_storage alignas(PAGE_SIZE);
     31 
     32 // __cfi_init is called by the loader as soon as the shadow is mapped. This may happen very early
     33 // during startup, before libdl.so global constructors, and, on i386, even before __libc_sysinfo is
     34 // initialized. This function should not do any system calls.
     35 extern "C" uintptr_t* __cfi_init(uintptr_t shadow_base) {
     36   shadow_base_storage.v = shadow_base;
     37   static_assert(sizeof(shadow_base_storage) == PAGE_SIZE, "");
     38   return &shadow_base_storage.v;
     39 }
     40 
     41 static uint16_t shadow_load(void* p) {
     42   uintptr_t addr = reinterpret_cast<uintptr_t>(p);
     43   uintptr_t ofs = CFIShadow::MemToShadowOffset(addr);
     44   if (ofs > CFIShadow::kShadowSize) return CFIShadow::kInvalidShadow;
     45   return *reinterpret_cast<uint16_t*>(shadow_base_storage.v + ofs);
     46 }
     47 
     48 static uintptr_t cfi_check_addr(uint16_t v, void* Ptr) {
     49   uintptr_t addr = reinterpret_cast<uintptr_t>(Ptr);
     50   uintptr_t aligned_addr = align_up(addr, CFIShadow::kShadowAlign);
     51   uintptr_t p = aligned_addr - (static_cast<uintptr_t>(v - CFIShadow::kRegularShadowMin)
     52                                 << CFIShadow::kCfiCheckGranularity);
     53 #ifdef __arm__
     54   // Assume Thumb encoding. FIXME: force thumb at compile time?
     55   p++;
     56 #endif
     57   return p;
     58 }
     59 
     60 static inline void cfi_slowpath_common(uint64_t CallSiteTypeId, void* Ptr, void* DiagData) {
     61   uint16_t v = shadow_load(Ptr);
     62   switch (v) {
     63     case CFIShadow::kInvalidShadow:
     64       __loader_cfi_fail(CallSiteTypeId, Ptr, DiagData, __builtin_return_address(0));
     65       break;
     66     case CFIShadow::kUncheckedShadow:
     67       break;
     68     default:
     69       reinterpret_cast<CFIShadow::CFICheckFn>(cfi_check_addr(v, Ptr))(CallSiteTypeId, Ptr, DiagData);
     70   }
     71 }
     72 
     73 extern "C" void __cfi_slowpath(uint64_t CallSiteTypeId, void* Ptr) {
     74   cfi_slowpath_common(CallSiteTypeId, Ptr, nullptr);
     75 }
     76 
     77 extern "C" void __cfi_slowpath_diag(uint64_t CallSiteTypeId, void* Ptr, void* DiagData) {
     78   cfi_slowpath_common(CallSiteTypeId, Ptr, DiagData);
     79 }
     80