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.
__cfi_init(uintptr_t shadow_base)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 // Returns the size of the CFI shadow mapping, or 0 if CFI is not (yet) used in this process.
__cfi_shadow_size()42 extern "C" size_t __cfi_shadow_size() {
43 return shadow_base_storage.v != 0 ? CFIShadow::kShadowSize : 0;
44 }
45
shadow_load(void * p)46 static uint16_t shadow_load(void* p) {
47 // Untag the pointer to move it into the address space covered by the shadow.
48 uintptr_t addr = reinterpret_cast<uintptr_t>(untag_address(p));
49 uintptr_t ofs = CFIShadow::MemToShadowOffset(addr);
50 if (ofs > CFIShadow::kShadowSize) return CFIShadow::kInvalidShadow;
51 return *reinterpret_cast<uint16_t*>(shadow_base_storage.v + ofs);
52 }
53
cfi_check_addr(uint16_t v,void * Ptr)54 static uintptr_t cfi_check_addr(uint16_t v, void* Ptr) {
55 uintptr_t addr = reinterpret_cast<uintptr_t>(Ptr);
56 // The aligned range of [0, kShadowAlign) uses a single shadow element, therefore all pointers in
57 // this range must get the same aligned_addr below. This matches CFIShadowWriter::Add; not the
58 // same as align_up().
59 uintptr_t aligned_addr = align_down(addr, CFIShadow::kShadowAlign) + CFIShadow::kShadowAlign;
60 uintptr_t p = aligned_addr - (static_cast<uintptr_t>(v - CFIShadow::kRegularShadowMin)
61 << CFIShadow::kCfiCheckGranularity);
62 #ifdef __arm__
63 // Assume Thumb encoding. FIXME: force thumb at compile time?
64 p++;
65 #endif
66 return p;
67 }
68
cfi_slowpath_common(uint64_t CallSiteTypeId,void * Ptr,void * DiagData)69 static inline void cfi_slowpath_common(uint64_t CallSiteTypeId, void* Ptr, void* DiagData) {
70 uint16_t v = shadow_load(Ptr);
71 switch (v) {
72 case CFIShadow::kInvalidShadow:
73 __loader_cfi_fail(CallSiteTypeId, Ptr, DiagData, __builtin_return_address(0));
74 break;
75 case CFIShadow::kUncheckedShadow:
76 break;
77 default:
78 reinterpret_cast<CFIShadow::CFICheckFn>(cfi_check_addr(v, Ptr))(CallSiteTypeId, Ptr, DiagData);
79 }
80 }
81
__cfi_slowpath(uint64_t CallSiteTypeId,void * Ptr)82 extern "C" void __cfi_slowpath(uint64_t CallSiteTypeId, void* Ptr) {
83 cfi_slowpath_common(CallSiteTypeId, Ptr, nullptr);
84 }
85
__cfi_slowpath_diag(uint64_t CallSiteTypeId,void * Ptr,void * DiagData)86 extern "C" void __cfi_slowpath_diag(uint64_t CallSiteTypeId, void* Ptr, void* DiagData) {
87 cfi_slowpath_common(CallSiteTypeId, Ptr, DiagData);
88 }
89