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fix: clarify signed & unsigned for jump insts #119

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fix: clarify signed & unsigned for jump insts #119

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f7ad168
fix: clarify signed & unsigned for jump insts
hsqStephenZhang Jan 11, 2025
8098c81
fix: add jmp insn unsigned extend unittest
hsqStephenZhang Jan 15, 2025
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20 changes: 14 additions & 6 deletions src/interpreter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,12 @@ pub fn execute_program(
insn_ptr = (insn_ptr as i16 + insn.off) as usize;
};

macro_rules! unsigned_u64 {
($imm:expr) => {
($imm as u32) as u64
};
}

match insn.opc {

// BPF_LD class
Expand Down Expand Up @@ -298,20 +304,22 @@ pub fn execute_program(

// BPF_JMP class
// TODO: check this actually works as expected for signed / unsigned ops
// J-EQ, J-NE, J-GT, J-GE, J-LT, J-LE: unsigned
// JS-GT, JS-GE, JS-LT, JS-LE: signed
ebpf::JA => do_jump(),
ebpf::JEQ_IMM => if reg[_dst] == insn.imm as u64 { do_jump(); },
ebpf::JEQ_IMM => if reg[_dst] == unsigned_u64!(insn.imm) { do_jump(); },
ebpf::JEQ_REG => if reg[_dst] == reg[_src] { do_jump(); },
ebpf::JGT_IMM => if reg[_dst] > insn.imm as u64 { do_jump(); },
ebpf::JGT_IMM => if reg[_dst] > unsigned_u64!(insn.imm) { do_jump(); },
ebpf::JGT_REG => if reg[_dst] > reg[_src] { do_jump(); },
ebpf::JGE_IMM => if reg[_dst] >= insn.imm as u64 { do_jump(); },
ebpf::JGE_IMM => if reg[_dst] >= unsigned_u64!(insn.imm) { do_jump(); },
ebpf::JGE_REG => if reg[_dst] >= reg[_src] { do_jump(); },
ebpf::JLT_IMM => if reg[_dst] < insn.imm as u64 { do_jump(); },
ebpf::JLT_IMM => if reg[_dst] < unsigned_u64!(insn.imm) { do_jump(); },
ebpf::JLT_REG => if reg[_dst] < reg[_src] { do_jump(); },
ebpf::JLE_IMM => if reg[_dst] <= insn.imm as u64 { do_jump(); },
ebpf::JLE_IMM => if reg[_dst] <= unsigned_u64!(insn.imm) { do_jump(); },
ebpf::JLE_REG => if reg[_dst] <= reg[_src] { do_jump(); },
ebpf::JSET_IMM => if reg[_dst] & insn.imm as u64 != 0 { do_jump(); },
ebpf::JSET_REG => if reg[_dst] & reg[_src] != 0 { do_jump(); },
ebpf::JNE_IMM => if reg[_dst] != insn.imm as u64 { do_jump(); },
ebpf::JNE_IMM => if reg[_dst] != unsigned_u64!(insn.imm) { do_jump(); },
ebpf::JNE_REG => if reg[_dst] != reg[_src] { do_jump(); },
ebpf::JSGT_IMM => if reg[_dst] as i64 > insn.imm as i64 { do_jump(); },
ebpf::JSGT_REG => if reg[_dst] as i64 > reg[_src] as i64 { do_jump(); },
Expand Down
32 changes: 32 additions & 0 deletions tests/ubpf_vm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -769,6 +769,38 @@ fn test_vm_jset_imm() {
assert_eq!(vm.execute_program().unwrap(), 0x1);
}

#[test]
fn test_vm_jmp_unsigned_extend() {
use rbpf::ebpf::{Insn, BE, EXIT, JEQ_IMM, MOV32_IMM, LD_W_REG};

// the insn `jeq r2, 0x80000000, +2` will be rejected
assert!(assemble("jeq r2, 0x80000000, +2").is_err());
// the prog is as follows:
// ldxw r2, [r1]
// be32 r2
// jeq r2, 0x80000000, +2 # 0x80000000 should be interpreted as 0x0000000080000000 (unsigned)
// mov32 r0, 2
// exit
// mov32 r0, 1
// exit
// we build it manually to bypass the verifier in `assemble(...)`
let insns = vec![
Insn { opc: LD_W_REG, dst: 2, src: 1, off: 0, imm: 0 },
Insn { opc: BE, dst: 2, src: 0, off: 0, imm: 32 },
Insn { opc: JEQ_IMM, dst: 2, src: 0, off: 2, imm: 0x80000000u32 as i32 },
Insn { opc: MOV32_IMM, dst: 0, src: 0, off: 0, imm: 2 },
Insn { opc: EXIT, dst: 0, src: 0, off: 0, imm: 0 },
Insn { opc: MOV32_IMM, dst: 0, src: 0, off: 0, imm: 1 },
Insn { opc: EXIT, dst: 0, src: 0, off: 0, imm: 0 }
];
let prog = insns.iter().map(|x| x.to_array()).flatten().collect::<Vec<u8>>();
let vm = rbpf::EbpfVmRaw::new(Some(&prog)).unwrap();
let mut data = vec![
0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
];
assert_eq!(vm.execute_program(&mut data).unwrap(), 1);
}

#[test]
fn test_vm_jset_reg() {
let prog = assemble("
Expand Down