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110 lines
4.5 KiB
Markdown
110 lines
4.5 KiB
Markdown
# Sandboxing PFFFT library
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This library was sandboxed as part of Google's summer 2020 internship program
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([blog post](https://security.googleblog.com/2020/12/improving-open-source-security-during.html)).
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Build System: CMake
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OS: Linux
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### How to use from an existing Project
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If your project does not include Sandboxed API as a dependency yet, add the
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following lines to the main `CMakeLists.txt`:
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```cmake
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include(FetchContent)
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FetchContent_Declare(sandboxed-api
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GIT_REPOSITORY https://github.com/google/sandboxed-api
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GIT_TAG main # Or pin a specific commit/tag
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)
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FetchContent_MakeAvailable(sandboxed-api) # CMake 3.14 or higher
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add_sapi_subdirectory(contrib/pffft)
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```
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The `add_sapi_subdirectory()` macro sets up the source and binary directories
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for the sandboxed jsonnet targets.
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Afterwards your project's code can link to `sapi_contrib::pffft` and use the
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generated header `pffft_sapi.sapi.h`. An example sandbox policy can be found
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in `main_pffft_sandboxed.cc`.
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### For testing:
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`cd build`, then `./pffft_sandboxed`
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### For debug:
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display custom info with
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`./pffft_sandboxed --logtostderr`
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## ***About the project***
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PFFFT library is concerned with 1D Fast-Fourier Transformations finding a
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compromise between accuracy and speed. It deals with real and complex
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vectors, both cases being illustrated in the testing part (`test_pffft.c`
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for initially and original version, `main_pffft_sandboxed.cc` for our
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currently implemented sandboxed version).
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The original files can be found at: https://bitbucket.org/jpommier/pffft/src.*
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The purpose of sandboxing is to limit the permissions and capabilities of
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library’s methods, in order to secure the usage of them.
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After obtaining the sandbox, the functions will be called through an
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Sandbox API (being called `api` in the current test) and so, the
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operations, system calls or namspaces access may be controlled.
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From both `pffft.h` and `fftpack.h` headers, useful methods are added to
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sapi library builded with CMake. There is also a need to link math library
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as the transformations made require mathematical operators.
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Regarding the testing of the methods, one main is doing this job by
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iterating through a set of values, that represents the accuracy of
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transformations and print the speed for each value and type of
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transformation. More specifically, the input length is the target for
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accuracy (named as `n`) and it stands for the number of data points from
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the series that calculate the result of transformation. It is also
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important to mention that the `complex` variable stands for a boolean value
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that tells the type of transformation (0 for REAL and 1 for COMPLEX) and
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it is taken into account while testing.
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In the end, the performance of PFFFT library it is outlined by the output.
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There are two output formats available, from which you can choose through
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`--output_format=` command-line flag.
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Without using this type of argument when running, the output format is set
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by default.*
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#### CMake observations resume:
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* linking pffft and fftpack (which contains necessary functions for pffft)
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* set math library
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#### Sandboxed main observations resume:
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* containing two testing parts (fft / pffft benchmarks)
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* showing the performance of the transformations implies
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testing them through various FFT dimenstions.
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Variable n, the input length, will take specific values
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meaning the number of points to which it is set the calculus
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(more details of mathematical purpose of n - https://en.wikipedia.org/wiki/Cooley%E2%80%93Tukey_FFT_algorithm).
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* output shows speed depending on the input length
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* use `--output_format=0` or `--output_format=1` arguments to choose between output formats.
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`0` is for a detailed output, while `1` is only displaying each transformation process speed.
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### Bugs history
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1. [Solved] pffft benchmark bug: "Sandbox not active"
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n = 64, status OK, `pffft_transform` generates error
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n > 64, status not OK
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Problem on initialising `absl::StatusOr<PFFFT_Setup *> s;` the memory that stays
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for s is not the same with the address passed in `pffft_transform` function.
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(`sapi::v::GenericPtr` - to be changed)
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Temporary solution: change the generated files to accept
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`uintptr_t` instead of `PFFFT_Setup`
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Solution: using `sapi::v::RemotePtr` instead of `sapi::v::GenericPtr`
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to access the memory of object `s`
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2. [Unresolved] compiling bug: "No space left on device"
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The building process creates some `embed` files that use lots of
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memory, trying to write them on `/tmp`.
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Temporary solution: clean /tmp directory by `sudo rm -rf /tmp/*`
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