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Follow-up for masks on shift operations #105

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merged 2 commits into from
Mar 15, 2024
Merged

Follow-up for masks on shift operations #105

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7e9f2e1
tests/ubpf_vm.rs: Add tests for arsh offset masking
qmonnet Mar 14, 2024
19a2be8
src/interpreter: Remove/explain masks for 32-bit shift operations
qmonnet Mar 15, 2024
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13 changes: 8 additions & 5 deletions src/interpreter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,6 @@ fn check_mem(addr: u64, len: usize, access_type: &str, insn_ptr: usize,
#[allow(cyclomatic_complexity)]
pub fn execute_program(prog_: Option<&[u8]>, mem: &[u8], mbuff: &[u8], helpers: &HashMap<u32, ebpf::Helper>) -> Result<u64, Error> {
const U32MAX: u64 = u32::MAX as u64;
const SHIFT_MASK_32: u32 = 0x1f;
const SHIFT_MASK_64: u64 = 0x3f;

let prog = match prog_ {
Expand Down Expand Up @@ -226,10 +225,12 @@ pub fn execute_program(prog_: Option<&[u8]>, mem: &[u8], mbuff: &[u8], helpers:
ebpf::OR32_REG => reg[_dst] = (reg[_dst] as u32 | reg[_src] as u32) as u64,
ebpf::AND32_IMM => reg[_dst] = (reg[_dst] as u32 & insn.imm as u32) as u64,
ebpf::AND32_REG => reg[_dst] = (reg[_dst] as u32 & reg[_src] as u32) as u64,
ebpf::LSH32_IMM => reg[_dst] = (reg[_dst] as u32).wrapping_shl(insn.imm as u32 & SHIFT_MASK_32) as u64,
ebpf::LSH32_REG => reg[_dst] = (reg[_dst] as u32).wrapping_shl(reg[_src] as u32 & SHIFT_MASK_32) as u64,
ebpf::RSH32_IMM => reg[_dst] = (reg[_dst] as u32).wrapping_shr(insn.imm as u32 & SHIFT_MASK_32) as u64,
ebpf::RSH32_REG => reg[_dst] = (reg[_dst] as u32).wrapping_shr(reg[_src] as u32 & SHIFT_MASK_32) as u64,
// As for the 64-bit version, we should mask the number of bits to shift with
// 0x1f, but .wrappping_shr() already takes care of it for us.
ebpf::LSH32_IMM => reg[_dst] = (reg[_dst] as u32).wrapping_shl(insn.imm as u32) as u64,
ebpf::LSH32_REG => reg[_dst] = (reg[_dst] as u32).wrapping_shl(reg[_src] as u32) as u64,
ebpf::RSH32_IMM => reg[_dst] = (reg[_dst] as u32).wrapping_shr(insn.imm as u32) as u64,
ebpf::RSH32_REG => reg[_dst] = (reg[_dst] as u32).wrapping_shr(reg[_src] as u32) as u64,
ebpf::NEG32 => { reg[_dst] = (reg[_dst] as i32).wrapping_neg() as u64; reg[_dst] &= U32MAX; },
ebpf::MOD32_IMM if insn.imm as u32 == 0 => (),
ebpf::MOD32_IMM => reg[_dst] = (reg[_dst] as u32 % insn.imm as u32) as u64,
Expand All @@ -239,6 +240,8 @@ pub fn execute_program(prog_: Option<&[u8]>, mem: &[u8], mbuff: &[u8], helpers:
ebpf::XOR32_REG => reg[_dst] = (reg[_dst] as u32 ^ reg[_src] as u32) as u64,
ebpf::MOV32_IMM => reg[_dst] = insn.imm as u32 as u64,
ebpf::MOV32_REG => reg[_dst] = (reg[_src] as u32) as u64,
// As for the 64-bit version, we should mask the number of bits to shift with
// 0x1f, but .wrappping_shr() already takes care of it for us.
ebpf::ARSH32_IMM => { reg[_dst] = (reg[_dst] as i32).wrapping_shr(insn.imm as u32) as u64; reg[_dst] &= U32MAX; },
ebpf::ARSH32_REG => { reg[_dst] = (reg[_dst] as i32).wrapping_shr(reg[_src] as u32) as u64; reg[_dst] &= U32MAX; },
ebpf::LE => {
Expand Down
46 changes: 46 additions & 0 deletions tests/ubpf_vm.rs
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Expand Up @@ -194,6 +194,52 @@ fn test_vm_arsh_reg() {
assert_eq!(vm.execute_program().unwrap(), 0xffff8000);
}

#[test]
fn test_vm_arsh_imm_overflow() {
let prog = assemble("
mov r0, 1
lsh r0, 63
arsh r0, 0xff20
exit").unwrap();
let vm = rbpf::EbpfVmNoData::new(Some(&prog)).unwrap();
assert_eq!(vm.execute_program().unwrap(), 0xffffffff80000000);
}

#[test]
fn test_vm_arsh_reg_overflow() {
let prog = assemble("
mov r0, 1
lsh r0, 63
mov r1, 0xff04
arsh r0, r1
exit").unwrap();
let vm = rbpf::EbpfVmNoData::new(Some(&prog)).unwrap();
assert_eq!(vm.execute_program().unwrap(), 0xf800000000000000);
}

#[test]
fn test_vm_arsh32_imm_overflow() {
let prog = assemble("
mov32 r0, 1
lsh32 r0, 31
arsh32 r0, 0xff10
exit").unwrap();
let vm = rbpf::EbpfVmNoData::new(Some(&prog)).unwrap();
assert_eq!(vm.execute_program().unwrap(), 0xffff8000);
}

#[test]
fn test_vm_arsh32_reg_overflow() {
let prog = assemble("
mov32 r0, 1
lsh32 r0, 31
mov32 r1, 32
arsh32 r0, r1
exit").unwrap();
let vm = rbpf::EbpfVmNoData::new(Some(&prog)).unwrap();
assert_eq!(vm.execute_program().unwrap(), 0x80000000);
}

#[test]
fn test_vm_be16() {
let prog = assemble("
Expand Down
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