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 "atomic_helpers.h"
14 #include "common.h"
15 #include "linux.h"
16 #include "mutex.h"
17 #include "string_utils.h"
18 
19 #include <errno.h>
20 #include <fcntl.h>
21 #include <linux/futex.h>
22 #include <sched.h>
23 #include <stdlib.h>
24 #include <string.h>
25 #include <sys/mman.h>
26 #include <sys/stat.h>
27 #include <sys/syscall.h>
28 #include <sys/time.h>
29 #include <time.h>
30 #include <unistd.h>
31 
32 #if SCUDO_ANDROID
33 #include <sys/prctl.h>
34 // Definitions of prctl arguments to set a vma name in Android kernels.
35 #define ANDROID_PR_SET_VMA 0x53564d41
36 #define ANDROID_PR_SET_VMA_ANON_NAME 0
37 #endif
38 
39 namespace scudo {
40 
41 uptr getPageSize() { return static_cast<uptr>(sysconf(_SC_PAGESIZE)); }
42 
43 void NORETURN die() { abort(); }
44 
45 void *map(void *Addr, uptr Size, UNUSED const char *Name, uptr Flags,
46           UNUSED MapPlatformData *Data) {
47   int MmapFlags = MAP_PRIVATE | MAP_ANONYMOUS;
48   int MmapProt;
49   if (Flags & MAP_NOACCESS) {
50     MmapFlags |= MAP_NORESERVE;
51     MmapProt = PROT_NONE;
52   } else {
53     MmapProt = PROT_READ | PROT_WRITE;
54   }
55 #if defined(__aarch64__)
56 #ifndef PROT_MTE
57 #define PROT_MTE 0x20
58 #endif
59   if (Flags & MAP_MEMTAG)
60     MmapProt |= PROT_MTE;
61 #endif
62   if (Addr) {
63     // Currently no scenario for a noaccess mapping with a fixed address.
64     DCHECK_EQ(Flags & MAP_NOACCESS, 0);
65     MmapFlags |= MAP_FIXED;
66   }
67   void *P = mmap(Addr, Size, MmapProt, MmapFlags, -1, 0);
68   if (P == MAP_FAILED) {
69     if (!(Flags & MAP_ALLOWNOMEM) || errno != ENOMEM)
70       dieOnMapUnmapError(errno == ENOMEM);
71     return nullptr;
72   }
73 #if SCUDO_ANDROID
74   if (Name)
75     prctl(ANDROID_PR_SET_VMA, ANDROID_PR_SET_VMA_ANON_NAME, P, Size, Name);
76 #endif
77   return P;
78 }
79 
80 void unmap(void *Addr, uptr Size, UNUSED uptr Flags,
81            UNUSED MapPlatformData *Data) {
82   if (munmap(Addr, Size) != 0)
83     dieOnMapUnmapError();
84 }
85 
86 void setMemoryPermission(uptr Addr, uptr Size, uptr Flags,
87                          UNUSED MapPlatformData *Data) {
88   int Prot = (Flags & MAP_NOACCESS) ? PROT_NONE : (PROT_READ | PROT_WRITE);
89   if (mprotect(reinterpret_cast<void *>(Addr), Size, Prot) != 0)
90     dieOnMapUnmapError();
91 }
92 
93 static bool madviseNeedsMemset() {
94   uptr Size = getPageSizeCached();
95   char *P = (char *)mmap(0, Size, PROT_READ | PROT_WRITE,
96                          MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
97   if (!P)
98     dieOnMapUnmapError(errno == ENOMEM);
99   *P = 1;
100   while (madvise(P, Size, MADV_DONTNEED) == -1 && errno == EAGAIN) {
101   }
102   bool R = (*P != 0);
103   if (munmap(P, Size) != 0)
104     dieOnMapUnmapError();
105   return R;
106 }
107 
108 static bool madviseNeedsMemsetCached() {
109   static atomic_u8 Cache;
110   enum State : u8 { Unknown = 0, Yes = 1, No = 2 };
111   State NeedsMemset = static_cast<State>(atomic_load_relaxed(&Cache));
112   if (NeedsMemset == Unknown) {
113     NeedsMemset = madviseNeedsMemset() ? Yes : No;
114     atomic_store_relaxed(&Cache, NeedsMemset);
115   }
116   return NeedsMemset == Yes;
117 }
118 
119 void releasePagesToOS(uptr BaseAddress, uptr Offset, uptr Size,
120                       UNUSED MapPlatformData *Data) {
121   void *Addr = reinterpret_cast<void *>(BaseAddress + Offset);
122   if (madviseNeedsMemsetCached()) {
123     // Workaround for QEMU-user ignoring MADV_DONTNEED.
124     // https://github.com/qemu/qemu/blob/b1cffefa1b163bce9aebc3416f562c1d3886eeaa/linux-user/syscall.c#L11941
125     memset(Addr, 0, Size);
126   }
127   while (madvise(Addr, Size, MADV_DONTNEED) == -1 && errno == EAGAIN) {
128   }
129 }
130 
131 // Calling getenv should be fine (c)(tm) at any time.
132 const char *getEnv(const char *Name) { return getenv(Name); }
133 
134 namespace {
135 enum State : u32 { Unlocked = 0, Locked = 1, Sleeping = 2 };
136 }
137 
138 bool HybridMutex::tryLock() {
139   return atomic_compare_exchange(&M, Unlocked, Locked) == Unlocked;
140 }
141 
142 // The following is based on https://akkadia.org/drepper/futex.pdf.
143 void HybridMutex::lockSlow() {
144   u32 V = atomic_compare_exchange(&M, Unlocked, Locked);
145   if (V == Unlocked)
146     return;
147   if (V != Sleeping)
148     V = atomic_exchange(&M, Sleeping, memory_order_acquire);
149   while (V != Unlocked) {
150     syscall(SYS_futex, reinterpret_cast<uptr>(&M), FUTEX_WAIT_PRIVATE, Sleeping,
151             nullptr, nullptr, 0);
152     V = atomic_exchange(&M, Sleeping, memory_order_acquire);
153   }
154 }
155 
156 void HybridMutex::unlock() {
157   if (atomic_fetch_sub(&M, 1U, memory_order_release) != Locked) {
158     atomic_store(&M, Unlocked, memory_order_release);
159     syscall(SYS_futex, reinterpret_cast<uptr>(&M), FUTEX_WAKE_PRIVATE, 1,
160             nullptr, nullptr, 0);
161   }
162 }
163 
164 u64 getMonotonicTime() {
165   timespec TS;
166   clock_gettime(CLOCK_MONOTONIC, &TS);
167   return static_cast<u64>(TS.tv_sec) * (1000ULL * 1000 * 1000) +
168          static_cast<u64>(TS.tv_nsec);
169 }
170 
171 u32 getNumberOfCPUs() {
172   cpu_set_t CPUs;
173   // sched_getaffinity can fail for a variety of legitimate reasons (lack of
174   // CAP_SYS_NICE, syscall filtering, etc), in which case we shall return 0.
175   if (sched_getaffinity(0, sizeof(cpu_set_t), &CPUs) != 0)
176     return 0;
177   return static_cast<u32>(CPU_COUNT(&CPUs));
178 }
179 
180 u32 getThreadID() {
181 #if SCUDO_ANDROID
182   return static_cast<u32>(gettid());
183 #else
184   return static_cast<u32>(syscall(SYS_gettid));
185 #endif
186 }
187 
188 // Blocking is possibly unused if the getrandom block is not compiled in.
189 bool getRandom(void *Buffer, uptr Length, UNUSED bool Blocking) {
190   if (!Buffer || !Length || Length > MaxRandomLength)
191     return false;
192   ssize_t ReadBytes;
193 #if defined(SYS_getrandom)
194 #if !defined(GRND_NONBLOCK)
195 #define GRND_NONBLOCK 1
196 #endif
197   // Up to 256 bytes, getrandom will not be interrupted.
198   ReadBytes =
199       syscall(SYS_getrandom, Buffer, Length, Blocking ? 0 : GRND_NONBLOCK);
200   if (ReadBytes == static_cast<ssize_t>(Length))
201     return true;
202 #endif // defined(SYS_getrandom)
203   // Up to 256 bytes, a read off /dev/urandom will not be interrupted.
204   // Blocking is moot here, O_NONBLOCK has no effect when opening /dev/urandom.
205   const int FileDesc = open("/dev/urandom", O_RDONLY);
206   if (FileDesc == -1)
207     return false;
208   ReadBytes = read(FileDesc, Buffer, Length);
209   close(FileDesc);
210   return (ReadBytes == static_cast<ssize_t>(Length));
211 }
212 
213 // Allocation free syslog-like API.
214 extern "C" WEAK int async_safe_write_log(int pri, const char *tag,
215                                          const char *msg);
216 
217 void outputRaw(const char *Buffer) {
218   if (&async_safe_write_log) {
219     constexpr s32 AndroidLogInfo = 4;
220     constexpr uptr MaxLength = 1024U;
221     char LocalBuffer[MaxLength];
222     while (strlen(Buffer) > MaxLength) {
223       uptr P;
224       for (P = MaxLength - 1; P > 0; P--) {
225         if (Buffer[P] == '\n') {
226           memcpy(LocalBuffer, Buffer, P);
227           LocalBuffer[P] = '\0';
228           async_safe_write_log(AndroidLogInfo, "scudo", LocalBuffer);
229           Buffer = &Buffer[P + 1];
230           break;
231         }
232       }
233       // If no newline was found, just log the buffer.
234       if (P == 0)
235         break;
236     }
237     async_safe_write_log(AndroidLogInfo, "scudo", Buffer);
238   } else {
239     (void)write(2, Buffer, strlen(Buffer));
240   }
241 }
242 
243 extern "C" WEAK void android_set_abort_message(const char *);
244 
245 void setAbortMessage(const char *Message) {
246   if (&android_set_abort_message)
247     android_set_abort_message(Message);
248 }
249 
250 } // namespace scudo
251 
252 #endif // SCUDO_LINUX
253