Abseil Common Libraries (C++) (grcp 依赖)
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96 lines
3.3 KiB
96 lines
3.3 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// base::AddressIsReadable() probes an address to see whether it is readable, |
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// without faulting. |
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#include "absl/debugging/internal/address_is_readable.h" |
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#if !defined(__linux__) || defined(__ANDROID__) |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace debugging_internal { |
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// On platforms other than Linux, just return true. |
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bool AddressIsReadable(const void* /* addr */) { return true; } |
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} // namespace debugging_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#else // __linux__ && !__ANDROID__ |
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#include <stdint.h> |
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#include <syscall.h> |
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#include <unistd.h> |
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#include "absl/base/internal/errno_saver.h" |
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#include "absl/base/internal/raw_logging.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace debugging_internal { |
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// NOTE: be extra careful about adding any interposable function calls here |
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// (such as open(), read(), etc.). These symbols may be interposed and will get |
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// invoked in contexts they don't expect. |
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// |
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// NOTE: any new system calls here may also require sandbox reconfiguration. |
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// |
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bool AddressIsReadable(const void *addr) { |
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// Align address on 8-byte boundary. On aarch64, checking last |
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// byte before inaccessible page returned unexpected EFAULT. |
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const uintptr_t u_addr = reinterpret_cast<uintptr_t>(addr) & ~7; |
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addr = reinterpret_cast<const void *>(u_addr); |
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// rt_sigprocmask below will succeed for this input. |
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if (addr == nullptr) return false; |
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absl::base_internal::ErrnoSaver errno_saver; |
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// Here we probe with some syscall which |
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// - accepts an 8-byte region of user memory as input |
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// - tests for EFAULT before other validation |
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// - has no problematic side-effects |
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// |
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// rt_sigprocmask(2) works for this. It copies sizeof(kernel_sigset_t)==8 |
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// bytes from the address into the kernel memory before any validation. |
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// |
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// The call can never succeed, since the `how` parameter is not one of |
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// SIG_BLOCK, SIG_UNBLOCK, SIG_SETMASK. |
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// |
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// This strategy depends on Linux implementation details, |
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// so we rely on the test to alert us if it stops working. |
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// |
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// Some discarded past approaches: |
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// - msync() doesn't reject PROT_NONE regions |
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// - write() on /dev/null doesn't return EFAULT |
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// - write() on a pipe requires creating it and draining the writes |
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// - connect() works but is problematic for sandboxes and needs a valid |
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// file descriptor |
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// |
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// This can never succeed (invalid first argument to sigprocmask). |
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ABSL_RAW_CHECK(syscall(SYS_rt_sigprocmask, ~0, addr, nullptr, |
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/*sizeof(kernel_sigset_t)*/ 8) == -1, |
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"unexpected success"); |
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ABSL_RAW_CHECK(errno == EFAULT || errno == EINVAL, "unexpected errno"); |
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return errno != EFAULT; |
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} |
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} // namespace debugging_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#endif // __linux__ && !__ANDROID__
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