diff options
Diffstat (limited to 'sys')
| -rw-r--r-- | sys/README.md | 229 |
1 files changed, 0 insertions, 229 deletions
diff --git a/sys/README.md b/sys/README.md deleted file mode 100644 index b5b497bc6..000000000 --- a/sys/README.md +++ /dev/null @@ -1,229 +0,0 @@ -# Syscall Description - -`syzkaller` uses declarative description of syscalls to generate, mutate, minimize, -serialize and deserialize programs (sequences of syscalls). Below you can see -(hopefully self-explanatory) excerpt from the description: - -``` -open(file filename, flags flags[open_flags], mode flags[open_mode]) fd -read(fd fd, buf buffer[out], count len[buf]) len[buf] -close(fd fd) -open_mode = S_IRUSR, S_IWUSR, S_IXUSR, S_IRGRP, S_IWGRP, S_IXGRP, S_IROTH, S_IWOTH, S_IXOTH -``` - -The description is contained in `sys/*.txt` files. See for example [sys/sys.txt](/sys/sys.txt) file. - -## Syntax - -Pseudo-formal grammar of syscall description: -``` - syscallname "(" [arg ["," arg]*] ")" [type] - arg = argname type - argname = identifier - type = typename [ "[" type-options "]" ] - typename = "const" | "intN" | "intptr" | "flags" | "array" | "ptr" | - "buffer" | "string" | "strconst" | "filename" | - "len" | "bytesize" | "vma" | "proc" - type-options = [type-opt ["," type-opt]] -``` -common type-options include: -``` - "opt" - the argument is optional (like mmap fd argument, or accept peer argument) -``` -rest of the type-options are type-specific: -``` - "const": integer constant, type-options: - value, underlying type (one if "intN", "intptr") - "intN"/"intptr": an integer without a particular meaning, type-options: - optional range of values (e.g. "5:10", or "-100:200") - "flags": a set of flags, type-options: - reference to flags description (see below) - "array": a variable/fixed-length array, type-options: - type of elements, optional size (fixed "5", or ranged "5:10", boundaries inclusive) - "ptr": a pointer to an object, type-options: - type of the object; direction (in/out/inout) - "buffer": a pointer to a memory buffer (like read/write buffer argument), type-options: - direction (in/out/inout) - "string": a zero-terminated memory buffer (no pointer indirection implied), type-options: - either a string value in quotes for constant strings (e.g. "foo"), - or a reference to string flags, - optionally followed by a buffer size (string values will be padded with \x00 to that size) - "filename": a file/link/dir name, no pointer indirection implied, in most cases you want `ptr[in, filename]` - "fileoff": offset within a file - "len": length of another field (for array it is number of elements), type-options: - argname of the object - "bytesize": similar to "len", but always denotes the size in bytes, type-options: - argname of the object - "vma": a pointer to a set of pages (used as input for mmap/munmap/mremap/madvise), type-options: - optional number of pages (e.g. vma[7]), or a range of pages (e.g. vma[2-4]) - "proc": per process int (see description below), type-options: - underlying type, value range start, how many values per process - "text16", "text32", "text64": machine code of the specified bitness -``` -flags/len/flags also have trailing underlying type type-option when used in structs/unions/pointers. - -Flags are described as: -``` - flagname = const ["," const]* -``` -or for string flags as: -``` - flagname = "\"" literal "\"" ["," "\"" literal "\""]* -``` - -### Ints - -You can use `int8`, `int16`, `int32`, `int64` and `int64` to denote an integer of the corresponding size. - -By appending `be` suffix (like `int16be`) integers become big-endian. - -It's possible to specify range of values for an integer in the format of `int32[0:100]`. - -To denote a bitfield of size N use `int64:N`. - -It's possible to use these various kinds of ints as base types for `const`, `flags`, `len` and `proc`. - -``` -example_struct { - f0 int8 # random 1-byte integer - f1 const[0x42, int16be] # const 2-byte integer with value 0x4200 (big-endian 0x42) - f2 int32[0:100] # random 4-byte integer with values from 0 to 100 inclusive - f3 int64:20 # random 20-bit bitfield -} -``` - -### Structs - -Structs are described as: -``` - structname "{" "\n" - (fieldname type "\n")+ - "}" -``` -Structs can have trailing attributes "packed" and "align_N", -they are specified in square brackets after the struct. - -### Unions - -Unions are described as: -``` - unionname "[" "\n" - (fieldname type "\n")+ - "]" -``` -Unions can have a trailing "varlen" attribute (specified in square brackets after the union), -which means that union length is not maximum of all option lengths, -but rather length of a particular chosen option. - -### Resources - -Custom resources are described as: -``` - resource identifier "[" underlying_type "]" [ ":" const ("," const)* ] -``` -`underlying_type` is either one of `int8`, `int16`, `int32`, `int64`, `intptr` or another resource. -Resources can then be used as types. For example: -``` -resource fd[int32]: 0xffffffffffffffff, AT_FDCWD, 1000000 -resource sock[fd] -resource sock_unix[sock] - -socket(...) sock -accept(fd sock, ...) sock -listen(fd sock, backlog int32) -``` - -### Length - -You can specify length of a particular field in struct or a named argument by using `len` and `bytesize` types, for example: -``` -write(fd fd, buf buffer[in], count len[buf]) len[buf] - -sock_fprog { - len len[filter, int16] - filter ptr[in, array[sock_filter]] -} -``` - -If `len`'s argument is a pointer (or a `buffer`), then the length of the pointee argument is used. - -To denote the length of a field in N-byte words use `bytesizeN`, possible values for N are 1, 2, 4 and 8. - -To denote the length of the parent struct, you can use `len[parent, int8]`. -To denote the length of the higher level parent when structs are embedded into one another, you can specify the type name of the particular parent: -``` -struct s1 { - f0 len[s2] # length of s2 -} - -struct s2 { - f0 s1 - f1 array[int32] -} - -``` - -### Proc - -The `proc` type can be used to denote per process integers. -The idea is to have a separate range of values for each executor, so they don't interfere. - -The simplest example is a port number. -The `proc[int16be, 20000, 4]` type means that we want to generate an `int16be` integer starting from `20000` and assign no more than `4` integers for each process. -As a result the executor number `n` will get values in the `[20000 + n * 4, 20000 + (n + 1) * 4)` range. - -### Misc - -Description files also contain `include` directives that refer to Linux kernel header files -and `define` directives that define symbolic constant values. See the following section for details. - -## Code generation - -Textual syscall descriptions are translated into code used by `syzkaller`. -This process consists of 2 steps. The first step is extraction of values of symbolic -constants from Linux sources using `syz-extract` utility. -`syz-extract` generates a small C program that includes kernel headers referenced -by `include` directives, defines macros as specified by `define` directives and -prints values of symbolic constants. Results are stored in `.const` files, one per arch. -For example, [sys/tty.txt](/sys/tty.txt) is translated into [sys/tty_amd64.const](/sys/tty_amd64.const). - -The second step is generation of Go code for syzkaller. This step uses syscall descriptions -and the const files generated during the first step. You can see a result in [sys/sys_amd64.go](/sys/sys_amd64.go) -and in [executor/syscalls.h](/executor/syscalls.h). - -## Describing new system calls - -This section describes how to extend syzkaller to allow fuzz testing of a new system call; -this is particularly useful for kernel developers who are proposing new system calls. - -First, add a declarative description of the new system call to the appropriate file: - - Various `sys/<subsystem>.txt` files hold system calls for particular kernel - subsystems, for example `bpf` or `socket`. - - [sys/sys.txt](/sys/sys.txt) holds descriptions for more general system calls. - - An entirely new subsystem can be added as a new `sys/<new>.txt` file. - -The description format is described [above](#syntax). - -If the subsystem is present in the mainline kernel, add the new txt file to `extract.sh` -file and run `make extract LINUX=$KSRC` with `KSRC` set to the location of a kernel -source tree. This will generate const files. - -If the subsystem is not present in the mainline kernel, then you need to manually -run `syz-extract` binary: -``` -make bin/syz-extract -bin/syz-extract -arch $ARCH -linux "$LINUX" -linuxbld "$LINUXBLD" sys/<new>.txt -``` -`$ARCH` is one of `amd64`, `arm64`, `ppc64le`. If the subsystem is supported on several architectures, -then run `syz-exctact` for each arch. -`$LINUX` should point to kernel source checkout, which is configured for the corresponding arch -(i.e. you need to run `make someconfig && make` there first). If the kernel was built into a separate -directory (with `make O=...`) then also set `$LINUXBLD` to the location of the -build directory. - -Then, run `make generate` which will update generated code. - -Rebuild syzkaller (`make clean all`) to force use of the new system call definitions. - -Optionally, adjust the `enable_syscalls` configuration value for syzkaller to specifically target the -new system calls. |