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To see description in Russian, please look at source:README_ru.md.

The repository contains ACSL specifications for the Linux kernel functions. The aim of the project is formal verification of Linux kernel library functions.

Papers

- D. Efremov, M. Mandrykin, Formal Verification of Linux Kernel Library Functions (in Russian) [PDF]
- D. Efremov, M. Mandrykin, A. Khoroshilov, Deductive Verification of Unmodified Linux Kernel Library Functions (will be published soon)

Proofs Status

ID Function Status Logic function libfuzzer Comment
1 check_bytes8 proved proved yes
2 match_string not required
3 memchr proved yes
4 memcmp proved yes
5 memscan proved not required yes
6 skip_spaces proved proved yes requires too strict (remove strlen)
7 strcasecmp proved yes
8 strcat proved not required usr strcmp in ensures
9 strchr proved proved yes
10 strchrnul proved proved yes
11 strcmp proved yes
12 strcpy proved not required use strcmp logic function
13 strcspn proved proved yes
14 strim not required !const
15 strlen proved proved yes
16 strncasecmp yes
17 strncat not required
18 strnchr proved yes
19 strncmp yes
20 strncpy not required
21 strnlen proved proved yes
22 strnstr yes
23 strpbrk proved proved yes
24 strrchr proved yes
25 strreplace not required !const
26 strsep proved not required !const
27 strspn proved proved yes
28 strstr yes
29 sysfs_streq yes
30 strlcat not required
31 strlcpy proved not required use strncmp lf in ensures
32 memmove proved(*) not required use memcmp logic function at ensures
33 memcpy proved not required use memcmp logic function at ensures
34 memset proved not required !const
35 kstrtobool proved not required yes
36 _parse_integer_fixup_radix proved not required yes
37 _parse_integer yes
(*) memmove - except pointer difference vc fail. Model limitation.

Toolchain

The specifications are developed in the ACSL language. Frama-C with AstraVer plugin are used for deductive verification. Installation instructions are available here.

Repository files

Each library function of the Linux kernel is located in a separate *.c file. The corresponding *.h file contains declarations, types, and structures specific to the function.

- The kernel_definitons.h file contains common for all functions types, macros, and other declarations.
- In ctype.h there are several functions, which were initially developed as macro. For the convenience of formal verification, these macro (islower, isupper, isdigit, ...) have been rewritten as an inline functions.

How to add a function in the repository

There is a tool called dismember in the [repository]. It is used to "transfer" the function code into a separate file.
Example (code for the strim function):

$ dismember -m ~/linux-stable/lib/string.c -k ~/linux-stable --double -f strim --output-dir .

Two files will be created: strim.c and strim.h

- -m - path to the file with function definition
- -k - path to the kernel directory
- -double - generate two files *.h and *.c
- -f - function name
- -output-dir - output directory

Specifications

The specification contract (precondition and postcondition) is located in the corresponding *.h file for each proved function (for example, strlen.h). A header file may also contain lemmas/axioms/logical functions if they are developed for a function.

A *.c file contain a body of a function with loops invariants, evaluation functions, and assertions.

For some functions, specifications are redundant. In fact, they describe function's behavior in two different ways. For example, the contract for the strlen function consists of a "regular" functional requirements and the requirement for correspondence of the returned result to the logical function strlen.

What is the reason for a such "redundancy"?

The logical function strlen is convenient to use in the other function's specification. For example, strcmp function (and strcmp logical function in the strcpy contract). All the basic properties of a logical functions are expressed in lemmas (lemmas are not proved at this stage). Such specifications can't be translated in the run-time assertions with E-ACSL plugin. Therefore, for those functions with a correspondent logical function, there are additionally exists a "usual" specification.

Criteria to develop a logical function:

1. It is possible to write a logical function only for a pure C function;
2. It is rational to write logical functions if they are useful for developing specifications of other functions. For example, in the memcpy contract, you can express the equality of src and dest by calling the memcmp logical function.

Full verification protocols (solver launches) are included (*.jessie folders) in the repository for the proved functions.

At the given stage, the correctness of the lemmas in the specifications is not proved in any way. Thus, they can contain contradictions. The lemmas will be proved at the second project stage by means of Coq or lemma functions.

How to run the tools

$ frama-c -jessie <func>.c
$ frama-c -jessie check_bytes8.c

Or

$ make verify-<func>
$ make verify-check_bytes8

LibFuzzer integration

[LibFuzzer] - is the library for function fuzzing. The status of functions fuzzing integration can be viewed in proved functions table. It is required to have clang compiler installed and libFuzzer.a in the project directory to run fuzzing.
How to run fuzzing:

$ make fuzz-<func>
$ make fuzz-check_bytes8