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// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/files/memory_mapped_file.h"
#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include "base/files/file_util.h"
#include "base/logging.h"
#include "base/numerics/safe_conversions.h"
#include "base/threading/scoped_blocking_call.h"
#include "build/build_config.h"
namespace base {
MemoryMappedFile::MemoryMappedFile() = default;
#if !BUILDFLAG(IS_NACL)
bool MemoryMappedFile::MapFileRegionToMemory(
const MemoryMappedFile::Region& region,
Access access) {
ScopedBlockingCall scoped_blocking_call(FROM_HERE, BlockingType::MAY_BLOCK);
off_t map_start = 0;
size_t map_size = 0u;
int32_t data_offset = 0;
size_t byte_size = 0u;
if (region == MemoryMappedFile::Region::kWholeFile) {
int64_t file_len = file_.GetLength();
if (file_len < 0) {
DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
return false;
}
if (!IsValueInRangeForNumericType<size_t>(file_len)) {
return false;
}
map_size = base::checked_cast<size_t>(file_len);
byte_size = map_size;
} else {
// The region can be arbitrarily aligned. mmap, instead, requires both the
// start and size to be page-aligned. Hence, we map here the page-aligned
// outer region [|aligned_start|, |aligned_start| + |size|] which contains
// |region| and then add up the |data_offset| displacement.
int64_t aligned_start = 0;
size_t aligned_size = 0u;
CalculateVMAlignedBoundaries(region.offset, region.size, &aligned_start,
&aligned_size, &data_offset);
// Ensure that the casts in the mmap call below are sane.
if (aligned_start < 0 ||
!IsValueInRangeForNumericType<off_t>(aligned_start)) {
DLOG(ERROR) << "Region bounds are not valid for mmap";
return false;
}
map_start = base::checked_cast<off_t>(aligned_start);
map_size = aligned_size;
byte_size = region.size;
}
if (map_size == 0u) {
// mmap() requires `map_size > 0`, and this ensures an empty span indicates
// invalid.
return false;
}
int prot = 0;
int flags = MAP_SHARED;
switch (access) {
case READ_ONLY:
prot |= PROT_READ;
break;
case READ_WRITE:
prot |= PROT_READ | PROT_WRITE;
break;
case READ_WRITE_COPY:
prot |= PROT_READ | PROT_WRITE;
flags = MAP_PRIVATE;
break;
case READ_WRITE_EXTEND:
prot |= PROT_READ | PROT_WRITE;
if (!AllocateFileRegion(&file_, region.offset, region.size)) {
return false;
}
break;
}
auto* ptr = static_cast<uint8_t*>(
mmap(nullptr, map_size, prot, flags, file_.GetPlatformFile(), map_start));
if (ptr == MAP_FAILED) {
DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
return false;
}
// SAFETY: For the span construction to be valid, `ptr` needs to point to at
// least `map_size` many bytes, which is the guarantee of mmap() when it
// returns a valid pointer, and that `data_offset + byte_size <= map_size`.
//
// If the mapping is of the whole file, `map_size == byte_size`
// and `data_offset == 0`, so `data_offset + byte_size <= map_size` is
// trivially satisfied.
//
// If the mapping is a sub-range of the file:
// - `aligned_start` is page aligned and <= `start`.
// - `map_size` is a multiple of the VM granularity and >=
// `byte_size`.
// - `data_offset` is the displacement of `start` w.r.t `aligned_start`.
// |..................|xxxxxxxxxxxxxxxxxx|.................|
// ^ aligned start ^ start | |
// ^------------------^ data_offset | |
// ^------------------^ byte_size |
// ^-------------------------------------------------------^ map_size
//
// The `data_offset` undoes the alignment of start. The `map_size` contains
// the padding before and after the mapped region to satisfy alignment. So
// the `data_offset + byte_size <= map_size`.
bytes_ = UNSAFE_BUFFERS(base::span(ptr + data_offset, byte_size));
return true;
}
#endif
void MemoryMappedFile::CloseHandles() {
ScopedBlockingCall scoped_blocking_call(FROM_HERE, BlockingType::MAY_BLOCK);
if (!bytes_.empty()) {
munmap(bytes_.data(), bytes_.size());
}
file_.Close();
bytes_ = base::span<uint8_t>();
}
} // namespace base
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