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verifier.rs
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verifier.rs
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// SPDX-License-Identifier: (Apache-2.0 OR MIT)
// Derived from uBPF <https://github.com/iovisor/ubpf>
// Copyright 2015 Big Switch Networks, Inc
// (uBPF: safety checks, originally in C)
// Copyright 2016 6WIND S.A. <quentin.monnet@6wind.com>
// (Translation to Rust)
// This “verifier” performs simple checks when the eBPF program is loaded into the VM (before it is
// interpreted or JIT-compiled). It has nothing to do with the much more elaborated verifier inside
// Linux kernel. There is no verification regarding the program flow control (should be a Direct
// Acyclic Graph) or the consistency for registers usage (the verifier of the kernel assigns types
// to the registers and is much stricter).
//
// On the other hand, rbpf is not expected to run in kernel space.
//
// Improving the verifier would be nice, but this is not trivial (and Linux kernel is under GPL
// license, so we cannot copy it).
//
// Contrary to the verifier of the Linux kernel, this one does not modify the bytecode at all.
use ebpf;
use std::io::{Error, ErrorKind};
fn reject<S: AsRef<str>>(msg: S) -> Result<(), Error> {
let full_msg = format!("[Verifier] Error: {}", msg.as_ref());
Err(Error::new(ErrorKind::Other, full_msg))
}
fn check_prog_len(prog: &[u8]) -> Result<(), Error> {
if prog.len() % ebpf::INSN_SIZE != 0 {
reject(format!("eBPF program length must be a multiple of {:?} octets",
ebpf::INSN_SIZE))?;
}
if prog.len() > ebpf::PROG_MAX_SIZE {
reject(format!("eBPF program length limited to {:?}, here {:?}",
ebpf::PROG_MAX_INSNS, prog.len() / ebpf::INSN_SIZE))?;
}
if prog.is_empty() {
reject("no program set, call set_program() to load one")?;
}
let last_opc = ebpf::get_insn(prog, (prog.len() / ebpf::INSN_SIZE) - 1).opc;
if last_opc & ebpf::BPF_CLS_MASK != ebpf::BPF_JMP {
reject("program does not end with “EXIT” instruction")?;
}
Ok(())
}
fn check_imm_endian(insn: &ebpf::Insn, insn_ptr: usize) -> Result<(), Error> {
match insn.imm {
16 | 32 | 64 => Ok(()),
_ => reject(format!("unsupported argument for LE/BE (insn #{insn_ptr:?})"))
}
}
fn check_load_dw(prog: &[u8], insn_ptr: usize) -> Result<(), Error> {
// We know we can reach next insn since we enforce an EXIT insn at the end of program, while
// this function should be called only for LD_DW insn, that cannot be last in program.
let next_insn = ebpf::get_insn(prog, insn_ptr + 1);
if next_insn.opc != 0 {
reject(format!("incomplete LD_DW instruction (insn #{insn_ptr:?})"))?;
}
Ok(())
}
fn check_jmp_offset(prog: &[u8], insn_ptr: usize) -> Result<(), Error> {
let insn = ebpf::get_insn(prog, insn_ptr);
if insn.off == -1 {
reject(format!("infinite loop (insn #{insn_ptr:?})"))?;
}
let dst_insn_ptr = insn_ptr as isize + 1 + insn.off as isize;
if dst_insn_ptr < 0 || dst_insn_ptr as usize >= (prog.len() / ebpf::INSN_SIZE) {
reject(format!("jump out of code to #{dst_insn_ptr:?} (insn #{insn_ptr:?})"))?;
}
let dst_insn = ebpf::get_insn(prog, dst_insn_ptr as usize);
if dst_insn.opc == 0 {
reject(format!("jump to middle of LD_DW at #{dst_insn_ptr:?} (insn #{insn_ptr:?})"))?;
}
Ok(())
}
fn check_registers(insn: &ebpf::Insn, store: bool, insn_ptr: usize) -> Result<(), Error> {
if insn.src > 10 {
reject(format!("invalid source register (insn #{insn_ptr:?})"))?;
}
match (insn.dst, store) {
(0 ..= 9, _) | (10, true) => Ok(()),
(10, false) => reject(format!("cannot write into register r10 (insn #{insn_ptr:?})")),
(_, _) => reject(format!("invalid destination register (insn #{insn_ptr:?})"))
}
}
pub fn check(prog: &[u8]) -> Result<(), Error> {
check_prog_len(prog)?;
let mut insn_ptr:usize = 0;
while insn_ptr * ebpf::INSN_SIZE < prog.len() {
let insn = ebpf::get_insn(prog, insn_ptr);
let mut store = false;
match insn.opc {
// BPF_LD class
ebpf::LD_ABS_B => {},
ebpf::LD_ABS_H => {},
ebpf::LD_ABS_W => {},
ebpf::LD_ABS_DW => {},
ebpf::LD_IND_B => {},
ebpf::LD_IND_H => {},
ebpf::LD_IND_W => {},
ebpf::LD_IND_DW => {},
ebpf::LD_DW_IMM => {
store = true;
check_load_dw(prog, insn_ptr)?;
insn_ptr += 1;
},
// BPF_LDX class
ebpf::LD_B_REG => {},
ebpf::LD_H_REG => {},
ebpf::LD_W_REG => {},
ebpf::LD_DW_REG => {},
// BPF_ST class
ebpf::ST_B_IMM => store = true,
ebpf::ST_H_IMM => store = true,
ebpf::ST_W_IMM => store = true,
ebpf::ST_DW_IMM => store = true,
// BPF_STX class
ebpf::ST_B_REG => store = true,
ebpf::ST_H_REG => store = true,
ebpf::ST_W_REG => store = true,
ebpf::ST_DW_REG => store = true,
ebpf::ST_W_XADD => { unimplemented!(); },
ebpf::ST_DW_XADD => { unimplemented!(); },
// BPF_ALU class
ebpf::ADD32_IMM => {},
ebpf::ADD32_REG => {},
ebpf::SUB32_IMM => {},
ebpf::SUB32_REG => {},
ebpf::MUL32_IMM => {},
ebpf::MUL32_REG => {},
ebpf::DIV32_IMM => {},
ebpf::DIV32_REG => {},
ebpf::OR32_IMM => {},
ebpf::OR32_REG => {},
ebpf::AND32_IMM => {},
ebpf::AND32_REG => {},
ebpf::LSH32_IMM => {},
ebpf::LSH32_REG => {},
ebpf::RSH32_IMM => {},
ebpf::RSH32_REG => {},
ebpf::NEG32 => {},
ebpf::MOD32_IMM => {},
ebpf::MOD32_REG => {},
ebpf::XOR32_IMM => {},
ebpf::XOR32_REG => {},
ebpf::MOV32_IMM => {},
ebpf::MOV32_REG => {},
ebpf::ARSH32_IMM => {},
ebpf::ARSH32_REG => {},
ebpf::LE => { check_imm_endian(&insn, insn_ptr)?; },
ebpf::BE => { check_imm_endian(&insn, insn_ptr)?; },
// BPF_ALU64 class
ebpf::ADD64_IMM => {},
ebpf::ADD64_REG => {},
ebpf::SUB64_IMM => {},
ebpf::SUB64_REG => {},
ebpf::MUL64_IMM => {},
ebpf::MUL64_REG => {},
ebpf::DIV64_IMM => {},
ebpf::DIV64_REG => {},
ebpf::OR64_IMM => {},
ebpf::OR64_REG => {},
ebpf::AND64_IMM => {},
ebpf::AND64_REG => {},
ebpf::LSH64_IMM => {},
ebpf::LSH64_REG => {},
ebpf::RSH64_IMM => {},
ebpf::RSH64_REG => {},
ebpf::NEG64 => {},
ebpf::MOD64_IMM => {},
ebpf::MOD64_REG => {},
ebpf::XOR64_IMM => {},
ebpf::XOR64_REG => {},
ebpf::MOV64_IMM => {},
ebpf::MOV64_REG => {},
ebpf::ARSH64_IMM => {},
ebpf::ARSH64_REG => {},
// BPF_JMP class
ebpf::JA => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JEQ_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JEQ_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGT_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGT_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGE_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGE_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLT_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLT_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLE_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLE_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSET_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSET_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JNE_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JNE_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGT_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGT_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGE_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGE_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLT_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLT_REG => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLE_IMM => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLE_REG => { check_jmp_offset(prog, insn_ptr)?; },
// BPF_JMP32 class
ebpf::JEQ_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JEQ_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGT_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGT_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGE_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JGE_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLT_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLT_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLE_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JLE_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSET_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSET_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JNE_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JNE_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGT_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGT_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGE_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSGE_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLT_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLT_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLE_IMM32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::JSLE_REG32 => { check_jmp_offset(prog, insn_ptr)?; },
ebpf::CALL => {},
ebpf::TAIL_CALL => { unimplemented!() },
ebpf::EXIT => {},
_ => {
reject(format!("unknown eBPF opcode {:#2x} (insn #{insn_ptr:?})", insn.opc))?;
},
}
check_registers(&insn, store, insn_ptr)?;
insn_ptr += 1;
}
// insn_ptr should now be equal to number of instructions.
if insn_ptr != prog.len() / ebpf::INSN_SIZE {
reject(format!("jumped out of code to #{insn_ptr:?}"))?;
}
Ok(())
}