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Member "abseil-cpp-20230802.1/absl/debugging/internal/address_is_readable.cc" (18 Sep 2023, 3400 Bytes) of package /linux/misc/abseil-cpp-20230802.1.tar.gz:

    1 // Copyright 2017 The Abseil Authors.
    2 //
    3 // Licensed under the Apache License, Version 2.0 (the "License");
    4 // you may not use this file except in compliance with the License.
    5 // You may obtain a copy of the License at
    6 //
    7 //      https://www.apache.org/licenses/LICENSE-2.0
    8 //
    9 // Unless required by applicable law or agreed to in writing, software
   10 // distributed under the License is distributed on an "AS IS" BASIS,
   11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   12 // See the License for the specific language governing permissions and
   13 // limitations under the License.
   14 
   15 // base::AddressIsReadable() probes an address to see whether it is readable,
   16 // without faulting.
   17 
   18 #include "absl/debugging/internal/address_is_readable.h"
   19 
   20 #if !defined(__linux__) || defined(__ANDROID__)
   21 
   22 namespace absl {
   23 ABSL_NAMESPACE_BEGIN
   24 namespace debugging_internal {
   25 
   26 // On platforms other than Linux, just return true.
   27 bool AddressIsReadable(const void* /* addr */) { return true; }
   28 
   29 }  // namespace debugging_internal
   30 ABSL_NAMESPACE_END
   31 }  // namespace absl
   32 
   33 #else  // __linux__ && !__ANDROID__
   34 
   35 #include <stdint.h>
   36 #include <syscall.h>
   37 #include <unistd.h>
   38 
   39 #include "absl/base/internal/errno_saver.h"
   40 #include "absl/base/internal/raw_logging.h"
   41 
   42 namespace absl {
   43 ABSL_NAMESPACE_BEGIN
   44 namespace debugging_internal {
   45 
   46 // NOTE: be extra careful about adding any interposable function calls here
   47 // (such as open(), read(), etc.). These symbols may be interposed and will get
   48 // invoked in contexts they don't expect.
   49 //
   50 // NOTE: any new system calls here may also require sandbox reconfiguration.
   51 //
   52 bool AddressIsReadable(const void *addr) {
   53   // Align address on 8-byte boundary. On aarch64, checking last
   54   // byte before inaccessible page returned unexpected EFAULT.
   55   const uintptr_t u_addr = reinterpret_cast<uintptr_t>(addr) & ~uintptr_t{7};
   56   addr = reinterpret_cast<const void *>(u_addr);
   57 
   58   // rt_sigprocmask below will succeed for this input.
   59   if (addr == nullptr) return false;
   60 
   61   absl::base_internal::ErrnoSaver errno_saver;
   62 
   63   // Here we probe with some syscall which
   64   // - accepts an 8-byte region of user memory as input
   65   // - tests for EFAULT before other validation
   66   // - has no problematic side-effects
   67   //
   68   // rt_sigprocmask(2) works for this.  It copies sizeof(kernel_sigset_t)==8
   69   // bytes from the address into the kernel memory before any validation.
   70   //
   71   // The call can never succeed, since the `how` parameter is not one of
   72   // SIG_BLOCK, SIG_UNBLOCK, SIG_SETMASK.
   73   //
   74   // This strategy depends on Linux implementation details,
   75   // so we rely on the test to alert us if it stops working.
   76   //
   77   // Some discarded past approaches:
   78   // - msync() doesn't reject PROT_NONE regions
   79   // - write() on /dev/null doesn't return EFAULT
   80   // - write() on a pipe requires creating it and draining the writes
   81   // - connect() works but is problematic for sandboxes and needs a valid
   82   //   file descriptor
   83   //
   84   // This can never succeed (invalid first argument to sigprocmask).
   85   ABSL_RAW_CHECK(syscall(SYS_rt_sigprocmask, ~0, addr, nullptr,
   86                          /*sizeof(kernel_sigset_t)*/ 8) == -1,
   87                  "unexpected success");
   88   ABSL_RAW_CHECK(errno == EFAULT || errno == EINVAL, "unexpected errno");
   89   return errno != EFAULT;
   90 }
   91 
   92 }  // namespace debugging_internal
   93 ABSL_NAMESPACE_END
   94 }  // namespace absl
   95 
   96 #endif  // __linux__ && !__ANDROID__