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Handle VFS reads into trapped memory regions

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pread will refuse to read into any trapped regions so implement a manual path with a staging buffer and memcpy for such cases
This commit is contained in:
Billy Laws 2022-05-10 18:33:55 +01:00
parent 1609fd2a32
commit d2acec24f5
1 changed files with 21 additions and 4 deletions
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25
app/src/main/cpp/skyline/vfs/os_backing.cpp
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@ -21,11 +21,28 @@ namespace skyline::vfs {
}
size_t OsBacking::ReadImpl(span<u8> output, size_t offset) {
auto ret{pread64(fd, output.data(), output.size(), static_cast<off64_t>(offset))};
if (ret < 0)
throw exception("Failed to read from fd: {}", strerror(errno));
size_t bytesRead{};
while (bytesRead < output.size()) {
auto ret{pread64(fd, output.data() + bytesRead, output.size() - bytesRead, static_cast<off64_t>(offset + bytesRead))};
if (ret < 0) {
if (errno == EFAULT) {
// If EFAULT is returned then we're reading into a trapped region so create a temporary buffer and read into that instead
// This is required since pread doesn't trigger signal handlers itself
std::vector<u8> buffer(output.size() - bytesRead);
ret = pread64(fd, buffer.data(), buffer.size(), static_cast<off64_t>(offset + bytesRead));
if (ret >= 0) {
output.subspan(bytesRead).copy_from(buffer);
bytesRead += static_cast<size_t>(ret);
continue;
}
}
return static_cast<size_t>(ret);
throw exception("Failed to read from fd: {}", strerror(errno));
} else {
bytesRead += static_cast<size_t>(ret);
}
}
return output.size();
}
size_t OsBacking::WriteImpl(span<u8> input, size_t offset) {