vyre 0.1.0

/// GPU-ready file metadata passed into bytecode evaluation.
#[repr(C)]
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
#[cfg_attr(feature = "gpu", derive(bytemuck::Pod, bytemuck::Zeroable))]
pub struct FileContext {
    /// Total file size in bytes.
    pub file_size: u32,
    /// Dominant entropy bucket.
    pub entropy_bucket: u32,
    /// First four bytes of the file.
    pub magic_u32: u32,
    /// Whether the file is a PE.
    pub is_pe: u32,
    /// Whether the PE is a DLL.
    pub is_dll: u32,
    /// Whether the PE is 64-bit.
    pub is_64bit: u32,
    /// Whether the PE carries an Authenticode directory.
    pub has_signature: u32,
    /// Number of PE sections.
    pub num_sections: u32,
    /// Number of PE imports.
    pub num_imports: u32,
    /// Entry point RVA.
    pub entry_point_rva: u32,
    /// Padding for WGSL alignment.
    pub _pad0: u32,
    /// Padding for WGSL alignment.
    pub _pad1: u32,
}

#[derive(Debug, Clone, Copy, Default)]
struct PeSummary {
    is_dll: bool,
    is_64bit: bool,
    has_signature: bool,
    num_sections: u16,
    num_imports: u32,
    entry_point_rva: u32,
}

impl FileContext {
    /// Build a compact context from raw bytes.
    pub fn from_bytes(data: &[u8]) -> Self {
        let pe = parse_pe_summary(data);
        Self {
            file_size: u32::try_from(data.len()).unwrap_or(u32::MAX),
            entropy_bucket: entropy_bucket(data) as u32,
            magic_u32: if data.len() >= 4 {
                u32::from_le_bytes([data[0], data[1], data[2], data[3]])
            } else {
                0
            },
            is_pe: pe.is_some() as u32,
            is_dll: pe.map(|value| value.is_dll as u32).unwrap_or(0),
            is_64bit: pe.map(|value| value.is_64bit as u32).unwrap_or(0),
            has_signature: pe.map(|value| value.has_signature as u32).unwrap_or(0),
            num_sections: pe.map(|value| value.num_sections as u32).unwrap_or(0),
            num_imports: pe.map(|value| value.num_imports).unwrap_or(0),
            entry_point_rva: pe.map(|value| value.entry_point_rva).unwrap_or(0),
            ..Self::default()
        }
    }
}

fn entropy_bucket(data: &[u8]) -> u8 {
    if data.is_empty() {
        return 0;
    }
    let mut counts = [0usize; 256];
    for byte in data {
        counts[*byte as usize] += 1;
    }
    let len = data.len() as f64;
    let mut entropy = 0.0f64;
    for count in counts {
        if count == 0 {
            continue;
        }
        let p = count as f64 / len;
        entropy -= p * p.log2();
    }
    ((entropy / 8.0) * 255.0).round().clamp(0.0, 255.0) as u8
}

fn parse_pe_summary(data: &[u8]) -> Option<PeSummary> {
    if data.len() < 0x40 || &data[..2] != b"MZ" {
        return None;
    }
    let pe_offset = read_u32(data, 0x3c)? as usize;
    if pe_offset.checked_add(0x18)? > data.len() || data.get(pe_offset..pe_offset + 4)? != b"PE\0\0" {
        return None;
    }

    let coff_offset = pe_offset + 4;
    let characteristics = read_u16(data, coff_offset + 18)?;
    let num_sections = read_u16(data, coff_offset + 2)?;
    let optional_size = read_u16(data, coff_offset + 16)? as usize;
    let optional_offset = coff_offset + 20;
    if optional_offset.checked_add(optional_size)? > data.len() || optional_size < 2 {
        return None;
    }

    let optional_magic = read_u16(data, optional_offset)?;
    let is_64bit = optional_magic == 0x20b;
    let data_dir_offset = if is_64bit {
        optional_offset + 112
    } else if optional_magic == 0x10b {
        optional_offset + 96
    } else {
        return None;
    };
    if data_dir_offset.checked_add(8 * 5)? > optional_offset + optional_size {
        return None;
    }

    let entry_point_rva = read_u32(data, optional_offset + 16).unwrap_or(0);
    let cert_rva = read_u32(data, data_dir_offset + 8 * 4).unwrap_or(0);
    let cert_size = read_u32(data, data_dir_offset + 8 * 4 + 4).unwrap_or(0);
    let import_rva = read_u32(data, data_dir_offset + 8).unwrap_or(0);
    let import_size = read_u32(data, data_dir_offset + 12).unwrap_or(0);

    let section_table = optional_offset + optional_size;
    let sections = parse_sections(data, section_table, num_sections as usize)?;
    let num_imports = count_pe_imports(data, &sections, import_rva, import_size, is_64bit).unwrap_or(0);

    Some(PeSummary {
        is_dll: (characteristics & 0x2000) != 0,
        is_64bit,
        has_signature: cert_rva != 0 && cert_size != 0,
        num_sections,
        num_imports,
        entry_point_rva,
    })
}

fn parse_sections(data: &[u8], offset: usize, count: usize) -> Option<Vec<(u32, u32, u32)>> {
    let table_len = count.checked_mul(40)?;
    if offset.checked_add(table_len)? > data.len() {
        return None;
    }
    let mut sections = Vec::with_capacity(count);
    for idx in 0..count {
        let base = offset + idx * 40;
        let virtual_size = read_u32(data, base + 8)?;
        let virtual_address = read_u32(data, base + 12)?;
        let raw_size = read_u32(data, base + 16)?;
        let raw_ptr = read_u32(data, base + 20)?;
        sections.push((virtual_address, virtual_size.max(raw_size), raw_ptr));
    }
    Some(sections)
}

fn count_pe_imports(
    data: &[u8],
    sections: &[(u32, u32, u32)],
    import_rva: u32,
    import_size: u32,
    is_64bit: bool,
) -> Option<u32> {
    if import_rva == 0 || import_size == 0 {
        return Some(0);
    }
    let import_offset = rva_to_offset(sections, import_rva)?;
    let import_limit = import_offset.checked_add(import_size as usize)?.min(data.len());
    let thunk_width = if is_64bit { 8usize } else { 4usize };
    let mut descriptor = import_offset;
    let mut imports = 0u32;

    while descriptor.checked_add(20)? <= import_limit {
        let original_first_thunk = read_u32(data, descriptor)?;
        let name_rva = read_u32(data, descriptor + 12)?;
        let first_thunk = read_u32(data, descriptor + 16)?;
        if original_first_thunk == 0 && name_rva == 0 && first_thunk == 0 {
            break;
        }
        let thunk_rva = if original_first_thunk != 0 {
            original_first_thunk
        } else {
            first_thunk
        };
        let mut thunk_offset = match rva_to_offset(sections, thunk_rva) {
            Some(value) => value,
            None => {
                descriptor += 20;
                continue;
            }
        };
        while thunk_offset.checked_add(thunk_width)? <= data.len() {
            let entry = if is_64bit {
                read_u64(data, thunk_offset)?
            } else {
                read_u32(data, thunk_offset)? as u64
            };
            if entry == 0 {
                break;
            }
            let ordinal_mask = if is_64bit { 1u64 << 63 } else { 1u64 << 31 };
            if (entry & ordinal_mask) == 0 {
                imports = imports.saturating_add(1);
            }
            thunk_offset += thunk_width;
        }
        descriptor += 20;
    }

    Some(imports)
}

fn rva_to_offset(sections: &[(u32, u32, u32)], rva: u32) -> Option<usize> {
    sections.iter().find_map(|(start, size, raw)| {
        let end = start.checked_add(*size)?;
        if (*start..end).contains(&rva) {
            Some((*raw).checked_add(rva - *start)? as usize)
        } else {
            None
        }
    })
}

fn read_u16(data: &[u8], offset: usize) -> Option<u16> {
    Some(u16::from_le_bytes(data.get(offset..offset + 2)?.try_into().ok()?))
}

fn read_u32(data: &[u8], offset: usize) -> Option<u32> {
    Some(u32::from_le_bytes(data.get(offset..offset + 4)?.try_into().ok()?))
}

fn read_u64(data: &[u8], offset: usize) -> Option<u64> {
    Some(u64::from_le_bytes(data.get(offset..offset + 8)?.try_into().ok()?))
}