1 //===-- linux.cpp -----------------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "platform.h"
10 
11 #if SCUDO_LINUX
12 
13 #include "common.h"
14 #include "linux.h"
15 #include "mutex.h"
16 #include "string_utils.h"
17 
18 #include <errno.h>
19 #include <fcntl.h>
20 #include <linux/futex.h>
21 #include <sched.h>
22 #include <stdlib.h>
23 #include <string.h>
24 #include <sys/mman.h>
25 #include <sys/stat.h>
26 #include <sys/syscall.h>
27 #include <sys/time.h>
28 #include <time.h>
29 #include <unistd.h>
30 
31 #if SCUDO_ANDROID
32 #include <sys/prctl.h>
33 // Definitions of prctl arguments to set a vma name in Android kernels.
34 #define ANDROID_PR_SET_VMA 0x53564d41
35 #define ANDROID_PR_SET_VMA_ANON_NAME 0
36 #endif
37 
38 namespace scudo {
39 
40 uptr getPageSize() { return static_cast<uptr>(sysconf(_SC_PAGESIZE)); }
41 
42 void NORETURN die() { abort(); }
43 
44 void *map(void *Addr, uptr Size, UNUSED const char *Name, uptr Flags,
45           UNUSED MapPlatformData *Data) {
46   int MmapFlags = MAP_PRIVATE | MAP_ANONYMOUS;
47   int MmapProt;
48   if (Flags & MAP_NOACCESS) {
49     MmapFlags |= MAP_NORESERVE;
50     MmapProt = PROT_NONE;
51   } else {
52     MmapProt = PROT_READ | PROT_WRITE;
53   }
54 #if defined(__aarch64__)
55 #ifndef PROT_MTE
56 #define PROT_MTE 0x20
57 #endif
58   if (Flags & MAP_MEMTAG)
59     MmapProt |= PROT_MTE;
60 #endif
61   if (Addr)
62     MmapFlags |= MAP_FIXED;
63   void *P = mmap(Addr, Size, MmapProt, MmapFlags, -1, 0);
64   if (P == MAP_FAILED) {
65     if (!(Flags & MAP_ALLOWNOMEM) || errno != ENOMEM)
66       dieOnMapUnmapError(errno == ENOMEM ? Size : 0);
67     return nullptr;
68   }
69 #if SCUDO_ANDROID
70   if (Name)
71     prctl(ANDROID_PR_SET_VMA, ANDROID_PR_SET_VMA_ANON_NAME, P, Size, Name);
72 #endif
73   return P;
74 }
75 
76 void unmap(void *Addr, uptr Size, UNUSED uptr Flags,
77            UNUSED MapPlatformData *Data) {
78   if (munmap(Addr, Size) != 0)
79     dieOnMapUnmapError();
80 }
81 
82 void setMemoryPermission(uptr Addr, uptr Size, uptr Flags,
83                          UNUSED MapPlatformData *Data) {
84   int Prot = (Flags & MAP_NOACCESS) ? PROT_NONE : (PROT_READ | PROT_WRITE);
85   if (mprotect(reinterpret_cast<void *>(Addr), Size, Prot) != 0)
86     dieOnMapUnmapError();
87 }
88 
89 void releasePagesToOS(uptr BaseAddress, uptr Offset, uptr Size,
90                       UNUSED MapPlatformData *Data) {
91   void *Addr = reinterpret_cast<void *>(BaseAddress + Offset);
92 
93   while (madvise(Addr, Size, MADV_DONTNEED) == -1 && errno == EAGAIN) {
94   }
95 }
96 
97 // Calling getenv should be fine (c)(tm) at any time.
98 const char *getEnv(const char *Name) { return getenv(Name); }
99 
100 namespace {
101 enum State : u32 { Unlocked = 0, Locked = 1, Sleeping = 2 };
102 }
103 
104 bool HybridMutex::tryLock() {
105   return atomic_compare_exchange(&M, Unlocked, Locked) == Unlocked;
106 }
107 
108 // The following is based on https://akkadia.org/drepper/futex.pdf.
109 void HybridMutex::lockSlow() {
110   u32 V = atomic_compare_exchange(&M, Unlocked, Locked);
111   if (V == Unlocked)
112     return;
113   if (V != Sleeping)
114     V = atomic_exchange(&M, Sleeping, memory_order_acquire);
115   while (V != Unlocked) {
116     syscall(SYS_futex, reinterpret_cast<uptr>(&M), FUTEX_WAIT_PRIVATE, Sleeping,
117             nullptr, nullptr, 0);
118     V = atomic_exchange(&M, Sleeping, memory_order_acquire);
119   }
120 }
121 
122 void HybridMutex::unlock() {
123   if (atomic_fetch_sub(&M, 1U, memory_order_release) != Locked) {
124     atomic_store(&M, Unlocked, memory_order_release);
125     syscall(SYS_futex, reinterpret_cast<uptr>(&M), FUTEX_WAKE_PRIVATE, 1,
126             nullptr, nullptr, 0);
127   }
128 }
129 
130 u64 getMonotonicTime() {
131   timespec TS;
132   clock_gettime(CLOCK_MONOTONIC, &TS);
133   return static_cast<u64>(TS.tv_sec) * (1000ULL * 1000 * 1000) +
134          static_cast<u64>(TS.tv_nsec);
135 }
136 
137 u32 getNumberOfCPUs() {
138   cpu_set_t CPUs;
139   // sched_getaffinity can fail for a variety of legitimate reasons (lack of
140   // CAP_SYS_NICE, syscall filtering, etc), in which case we shall return 0.
141   if (sched_getaffinity(0, sizeof(cpu_set_t), &CPUs) != 0)
142     return 0;
143   return static_cast<u32>(CPU_COUNT(&CPUs));
144 }
145 
146 u32 getThreadID() {
147 #if SCUDO_ANDROID
148   return static_cast<u32>(gettid());
149 #else
150   return static_cast<u32>(syscall(SYS_gettid));
151 #endif
152 }
153 
154 // Blocking is possibly unused if the getrandom block is not compiled in.
155 bool getRandom(void *Buffer, uptr Length, UNUSED bool Blocking) {
156   if (!Buffer || !Length || Length > MaxRandomLength)
157     return false;
158   ssize_t ReadBytes;
159 #if defined(SYS_getrandom)
160 #if !defined(GRND_NONBLOCK)
161 #define GRND_NONBLOCK 1
162 #endif
163   // Up to 256 bytes, getrandom will not be interrupted.
164   ReadBytes =
165       syscall(SYS_getrandom, Buffer, Length, Blocking ? 0 : GRND_NONBLOCK);
166   if (ReadBytes == static_cast<ssize_t>(Length))
167     return true;
168 #endif // defined(SYS_getrandom)
169   // Up to 256 bytes, a read off /dev/urandom will not be interrupted.
170   // Blocking is moot here, O_NONBLOCK has no effect when opening /dev/urandom.
171   const int FileDesc = open("/dev/urandom", O_RDONLY);
172   if (FileDesc == -1)
173     return false;
174   ReadBytes = read(FileDesc, Buffer, Length);
175   close(FileDesc);
176   return (ReadBytes == static_cast<ssize_t>(Length));
177 }
178 
179 // Allocation free syslog-like API.
180 extern "C" WEAK int async_safe_write_log(int pri, const char *tag,
181                                          const char *msg);
182 
183 void outputRaw(const char *Buffer) {
184   if (&async_safe_write_log) {
185     constexpr s32 AndroidLogInfo = 4;
186     constexpr uptr MaxLength = 1024U;
187     char LocalBuffer[MaxLength];
188     while (strlen(Buffer) > MaxLength) {
189       uptr P;
190       for (P = MaxLength - 1; P > 0; P--) {
191         if (Buffer[P] == '\n') {
192           memcpy(LocalBuffer, Buffer, P);
193           LocalBuffer[P] = '\0';
194           async_safe_write_log(AndroidLogInfo, "scudo", LocalBuffer);
195           Buffer = &Buffer[P + 1];
196           break;
197         }
198       }
199       // If no newline was found, just log the buffer.
200       if (P == 0)
201         break;
202     }
203     async_safe_write_log(AndroidLogInfo, "scudo", Buffer);
204   } else {
205     (void)write(2, Buffer, strlen(Buffer));
206   }
207 }
208 
209 extern "C" WEAK void android_set_abort_message(const char *);
210 
211 void setAbortMessage(const char *Message) {
212   if (&android_set_abort_message)
213     android_set_abort_message(Message);
214 }
215 
216 } // namespace scudo
217 
218 #endif // SCUDO_LINUX
219