refactor: align platform crate boundaries

senbei-elf/src/layout.rs

@@ -0,0 +1,636 @@
+use crate::{Error, Result, invalid};
+
+pub const SHT_NOBITS: u32 = 8;
+pub const SHT_STRTAB: u32 = 3;
+pub const SHT_LOUSER: u32 = 0x8000_0000;
+pub const SHF_ALLOC: u64 = 2;
+const PT_LOAD: u32 = 1;
+pub const PF_R: u32 = 4;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct LoadSegment {
+    pub offset: u64,
+    pub virtual_address: u64,
+    pub file_size: u64,
+    pub memory_size: u64,
+    pub flags: u32,
+    pub alignment: u64,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SectionHeader {
+    pub name: u32,
+    pub section_type: u32,
+    pub flags: u64,
+    pub address: u64,
+    pub offset: u64,
+    pub size: u64,
+    pub link: u32,
+    pub info: u32,
+    pub alignment: u64,
+    pub entry_size: u64,
+}
+
+impl SectionHeader {
+    pub const SIZE: usize = 0x40;
+
+    fn parse(data: &[u8], offset: usize) -> Result<Self> {
+        Ok(Self {
+            name: read_u32(data, offset)?,
+            section_type: read_u32(data, offset + 4)?,
+            flags: read_u64(data, offset + 8)?,
+            address: read_u64(data, offset + 0x10)?,
+            offset: read_u64(data, offset + 0x18)?,
+            size: read_u64(data, offset + 0x20)?,
+            link: read_u32(data, offset + 0x28)?,
+            info: read_u32(data, offset + 0x2c)?,
+            alignment: read_u64(data, offset + 0x30)?,
+            entry_size: read_u64(data, offset + 0x38)?,
+        })
+    }
+
+    pub fn encode(self) -> [u8; Self::SIZE] {
+        let mut output = [0_u8; Self::SIZE];
+        output[0..4].copy_from_slice(&self.name.to_le_bytes());
+        output[4..8].copy_from_slice(&self.section_type.to_le_bytes());
+        output[8..0x10].copy_from_slice(&self.flags.to_le_bytes());
+        output[0x10..0x18].copy_from_slice(&self.address.to_le_bytes());
+        output[0x18..0x20].copy_from_slice(&self.offset.to_le_bytes());
+        output[0x20..0x28].copy_from_slice(&self.size.to_le_bytes());
+        output[0x28..0x2c].copy_from_slice(&self.link.to_le_bytes());
+        output[0x2c..0x30].copy_from_slice(&self.info.to_le_bytes());
+        output[0x30..0x38].copy_from_slice(&self.alignment.to_le_bytes());
+        output[0x38..0x40].copy_from_slice(&self.entry_size.to_le_bytes());
+        output
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ElfLayout {
+    pub entrypoint: u64,
+    pub program_header_offset: usize,
+    pub program_header_size: usize,
+    pub program_header_count: usize,
+    pub program_headers: Vec<LoadSegment>,
+    pub section_headers: Vec<SectionHeader>,
+    pub section_name_index: usize,
+    pub private_section_index: usize,
+}
+
+impl ElfLayout {
+    pub fn parse(data: &[u8], require_private: bool) -> Result<Self> {
+        let ident = slice(data, 0, 6)?;
+        if ident[..4] != *b"\x7fELF" || ident[4] != 2 || ident[5] != 1 {
+            return invalid("input is not a little-endian ELF64 file");
+        }
+        if read_u16(data, 0x12)? != crate::AARCH64_MACHINE {
+            return invalid("input is not an AArch64 ELF");
+        }
+        let entrypoint = read_u64(data, 0x18)?;
+        let program_header_offset = usize_from_u64(read_u64(data, 0x20)?, "program header offset")?;
+        let section_header_offset = usize_from_u64(read_u64(data, 0x28)?, "section header offset")?;
+        let program_header_size = usize::from(read_u16(data, 0x36)?);
+        let program_header_count = usize::from(read_u16(data, 0x38)?);
+        let section_header_size = usize::from(read_u16(data, 0x3a)?);
+        let section_header_count = usize::from(read_u16(data, 0x3c)?);
+        let section_name_index = usize::from(read_u16(data, 0x3e)?);
+        if program_header_size != 0x38 || section_header_size != SectionHeader::SIZE {
+            return invalid("unexpected ELF program/section header size");
+        }
+
+        let mut program_headers = Vec::new();
+        for index in 0..program_header_count {
+            let offset = checked_index(program_header_offset, index, program_header_size)?;
+            if read_u32(data, offset)? != PT_LOAD {
+                continue;
+            }
+            let segment = LoadSegment {
+                flags: read_u32(data, offset + 4)?,
+                offset: read_u64(data, offset + 8)?,
+                virtual_address: read_u64(data, offset + 0x10)?,
+                file_size: read_u64(data, offset + 0x20)?,
+                memory_size: read_u64(data, offset + 0x28)?,
+                alignment: read_u64(data, offset + 0x30)?,
+            };
+            let file_end = segment
+                .offset
+                .checked_add(segment.file_size)
+                .ok_or_else(|| Error::Invalid(format!("PT_LOAD {index} file range overflow")))?;
+            if file_end > data.len() as u64 {
+                return invalid(format!("PT_LOAD {index} exceeds input file"));
+            }
+            program_headers.push(segment);
+        }
+        if program_headers.is_empty() {
+            return invalid("input ELF contains no PT_LOAD segments");
+        }
+
+        let mut section_headers = Vec::with_capacity(section_header_count);
+        for index in 0..section_header_count {
+            let offset = checked_index(section_header_offset, index, section_header_size)?;
+            section_headers.push(SectionHeader::parse(data, offset)?);
+        }
+        if section_name_index >= section_headers.len() {
+            return invalid("ELF section-name index is out of range");
+        }
+        let private = section_headers
+            .iter()
+            .enumerate()
+            .filter_map(|(index, section)| (section.section_type == SHT_LOUSER).then_some(index))
+            .collect::<Vec<_>>();
+        let private_section_index = match private.as_slice() {
+            [index] => *index,
+            [] if !require_private => usize::MAX,
+            _ => {
+                return invalid(format!(
+                    "expected {} SHT_LOUSER section, found {}",
+                    if require_private {
+                        "one"
+                    } else {
+                        "at most one"
+                    },
+                    private.len()
+                ));
+            }
+        };
+        let layout = Self {
+            entrypoint,
+            program_header_offset,
+            program_header_size,
+            program_header_count,
+            program_headers,
+            section_headers,
+            section_name_index,
+            private_section_index,
+        };
+        // Section roles are resolved from the ELF's own string table. Validate
+        // it at the format boundary so callers cannot silently continue with
+        // fabricated or lossy section names.
+        layout.section_names(data)?;
+        Ok(layout)
+    }
+
+    pub fn private_section(&self) -> Result<SectionHeader> {
+        self.section_headers
+            .get(self.private_section_index)
+            .copied()
+            .ok_or_else(|| Error::Invalid("ELF has no private section".to_owned()))
+    }
+
+    pub fn load_end(&self) -> Result<u64> {
+        self.program_headers
+            .iter()
+            .map(|segment| {
+                segment
+                    .virtual_address
+                    .checked_add(segment.memory_size)
+                    .ok_or_else(|| Error::Invalid("PT_LOAD memory end overflow".to_owned()))
+            })
+            .collect::<Result<Vec<_>>>()?
+            .into_iter()
+            .max()
+            .ok_or_else(|| Error::Invalid("ELF has no PT_LOAD memory range".to_owned()))
+    }
+
+    pub fn file_load_end(&self) -> Result<u64> {
+        self.program_headers
+            .iter()
+            .map(|segment| {
+                segment
+                    .offset
+                    .checked_add(segment.file_size)
+                    .ok_or_else(|| Error::Invalid("PT_LOAD file end overflow".to_owned()))
+            })
+            .collect::<Result<Vec<_>>>()?
+            .into_iter()
+            .max()
+            .ok_or_else(|| Error::Invalid("ELF has no PT_LOAD file range".to_owned()))
+    }
+
+    pub fn load_alignment(&self) -> Result<u64> {
+        let alignment = self
+            .program_headers
+            .iter()
+            .map(|segment| segment.alignment)
+            .max()
+            .ok_or_else(|| Error::Invalid("ELF has no PT_LOAD alignment".to_owned()))?;
+        if alignment == 0 || !alignment.is_power_of_two() {
+            return invalid(format!("invalid PT_LOAD alignment 0x{alignment:x}"));
+        }
+        Ok(alignment)
+    }
+
+    pub fn append_load_segment(&self, output: &mut [u8], segment: LoadSegment) -> Result<Self> {
+        if self.program_header_size != 0x38 {
+            return invalid("unexpected ELF program header size");
+        }
+        if segment.file_size == 0 {
+            return invalid("new PT_LOAD has no file contents");
+        }
+        if segment.memory_size < segment.file_size {
+            return invalid("new PT_LOAD memory size is smaller than file size");
+        }
+        if segment.alignment == 0 || !segment.alignment.is_power_of_two() {
+            return invalid(format!(
+                "invalid new PT_LOAD alignment 0x{:x}",
+                segment.alignment
+            ));
+        }
+        if segment.offset % segment.alignment != segment.virtual_address % segment.alignment {
+            return invalid("new PT_LOAD offset and address are misaligned");
+        }
+        let segment_file_end = segment
+            .offset
+            .checked_add(segment.file_size)
+            .ok_or_else(|| Error::Invalid("new PT_LOAD file range overflow".to_owned()))?;
+        let segment_memory_end = segment
+            .virtual_address
+            .checked_add(segment.memory_size)
+            .ok_or_else(|| Error::Invalid("new PT_LOAD memory range overflow".to_owned()))?;
+        if segment_file_end > output.len() as u64 {
+            return invalid("new PT_LOAD exceeds output mapping");
+        }
+        for existing in &self.program_headers {
+            let existing_file_end = existing
+                .offset
+                .checked_add(existing.file_size)
+                .ok_or_else(|| Error::Invalid("PT_LOAD file range overflow".to_owned()))?;
+            if segment.offset < existing_file_end && existing.offset < segment_file_end {
+                return invalid("new PT_LOAD overlaps an existing file range");
+            }
+            let existing_memory_end = existing
+                .virtual_address
+                .checked_add(existing.memory_size)
+                .ok_or_else(|| Error::Invalid("PT_LOAD memory range overflow".to_owned()))?;
+            if segment.virtual_address < existing_memory_end
+                && existing.virtual_address < segment_memory_end
+            {
+                return invalid("new PT_LOAD overlaps an existing memory range");
+            }
+        }
+        let new_count = self
+            .program_header_count
+            .checked_add(1)
+            .ok_or_else(|| Error::Invalid("program header count overflow".to_owned()))?;
+        let new_count_u16 = u16::try_from(new_count)
+            .map_err(|_| Error::Invalid("program header count exceeds u16".to_owned()))?;
+        let header_offset = checked_index(
+            self.program_header_offset,
+            self.program_header_count,
+            self.program_header_size,
+        )?;
+        let header_end = header_offset
+            .checked_add(self.program_header_size)
+            .ok_or_else(|| Error::Invalid("new program header range overflow".to_owned()))?;
+        slice(output, header_offset, self.program_header_size)?;
+        let first_file_section = self
+            .section_headers
+            .iter()
+            .filter(|section| section.section_type != SHT_NOBITS && section.size != 0)
+            .map(|section| section.offset)
+            .min();
+        if first_file_section.is_some_and(|offset| header_end as u64 > offset) {
+            return invalid("no space for an additional program header");
+        }
+
+        let mut header = [0_u8; 0x38];
+        header[0..4].copy_from_slice(&PT_LOAD.to_le_bytes());
+        header[4..8].copy_from_slice(&segment.flags.to_le_bytes());
+        header[8..0x10].copy_from_slice(&segment.offset.to_le_bytes());
+        header[0x10..0x18].copy_from_slice(&segment.virtual_address.to_le_bytes());
+        header[0x18..0x20].copy_from_slice(&segment.virtual_address.to_le_bytes());
+        header[0x20..0x28].copy_from_slice(&segment.file_size.to_le_bytes());
+        header[0x28..0x30].copy_from_slice(&segment.memory_size.to_le_bytes());
+        header[0x30..0x38].copy_from_slice(&segment.alignment.to_le_bytes());
+        output
+            .get_mut(header_offset..header_end)
+            .ok_or_else(|| Error::Invalid("new program header exceeds output".to_owned()))?
+            .copy_from_slice(&header);
+        output
+            .get_mut(0x38..0x3a)
+            .ok_or_else(|| Error::Invalid("ELF header is truncated".to_owned()))?
+            .copy_from_slice(&new_count_u16.to_le_bytes());
+
+        let mut updated = self.clone();
+        updated.program_header_count = new_count;
+        updated.program_headers.push(segment);
+        Ok(updated)
+    }
+
+    /// Resolve every section's name from the ELF `shstrtab` section.
+    ///
+    /// The returned names are source data, not role labels supplied by the
+    /// caller. Any malformed string-table reference is an input error.
+    pub fn section_names(&self, data: &[u8]) -> Result<Vec<String>> {
+        let table = self
+            .section_headers
+            .get(self.section_name_index)
+            .copied()
+            .ok_or_else(|| Error::Invalid("ELF section-name index is out of range".to_owned()))?;
+        if table.section_type != SHT_STRTAB {
+            return invalid(format!(
+                "ELF section-name table has unexpected type 0x{:x}",
+                table.section_type
+            ));
+        }
+        let strings = slice_u64(data, table.offset, table.size)?;
+        if strings.is_empty() || strings[0] != 0 {
+            return invalid("ELF section-name table does not start with NUL");
+        }
+        if strings.last().copied() != Some(0) {
+            return invalid("ELF section-name table is not NUL terminated");
+        }
+        self.section_headers
+            .iter()
+            .enumerate()
+            .map(|(index, section)| {
+                let offset = section.name as usize;
+                if offset >= strings.len() {
+                    return invalid(format!(
+                        "ELF section {index} name offset 0x{offset:x} exceeds section-name table"
+                    ));
+                }
+                let end = strings[offset..]
+                    .iter()
+                    .position(|&byte| byte == 0)
+                    .map(|length| offset + length)
+                    .ok_or_else(|| {
+                        Error::Invalid(format!(
+                            "ELF section {index} name at 0x{offset:x} is unterminated"
+                        ))
+                    })?;
+                let name = std::str::from_utf8(&strings[offset..end]).map_err(|error| {
+                    Error::Invalid(format!(
+                        "ELF section {index} name at 0x{offset:x} is not UTF-8: {error}"
+                    ))
+                })?;
+                if index == 0 && section.name != 0 {
+                    return invalid("ELF null section has a nonzero name offset");
+                }
+                Ok(name.to_owned())
+            })
+            .collect()
+    }
+
+    pub fn file_offset_to_virtual_address(&self, offset: u64, size: u64) -> Result<u64> {
+        let end = offset
+            .checked_add(size)
+            .ok_or_else(|| Error::Invalid("file range overflow".to_owned()))?;
+        for segment in &self.program_headers {
+            let segment_end = segment
+                .offset
+                .checked_add(segment.file_size)
+                .ok_or_else(|| Error::Invalid("PT_LOAD file range overflow".to_owned()))?;
+            if segment.offset <= offset && end <= segment_end {
+                return segment
+                    .virtual_address
+                    .checked_add(offset - segment.offset)
+                    .ok_or_else(|| Error::Invalid("virtual address overflow".to_owned()));
+            }
+        }
+        invalid(format!(
+            "file range 0x{offset:x}..0x{end:x} is not in PT_LOAD"
+        ))
+    }
+}
+
+pub fn slice(data: &[u8], offset: usize, size: usize) -> Result<&[u8]> {
+    let end = offset
+        .checked_add(size)
+        .ok_or_else(|| Error::Invalid("byte range overflow".to_owned()))?;
+    data.get(offset..end).ok_or_else(|| {
+        Error::Invalid(format!(
+            "byte range 0x{offset:x}..0x{end:x} is out of bounds"
+        ))
+    })
+}
+
+pub fn slice_u64(data: &[u8], offset: u64, size: u64) -> Result<&[u8]> {
+    slice(
+        data,
+        usize_from_u64(offset, "file offset")?,
+        usize_from_u64(size, "file size")?,
+    )
+}
+
+pub fn read_u16(data: &[u8], offset: usize) -> Result<u16> {
+    let bytes: [u8; 2] = slice(data, offset, 2)?
+        .try_into()
+        .map_err(|_| Error::Invalid("invalid u16 range".to_owned()))?;
+    Ok(u16::from_le_bytes(bytes))
+}
+
+pub fn read_u32(data: &[u8], offset: usize) -> Result<u32> {
+    let bytes: [u8; 4] = slice(data, offset, 4)?
+        .try_into()
+        .map_err(|_| Error::Invalid("invalid u32 range".to_owned()))?;
+    Ok(u32::from_le_bytes(bytes))
+}
+
+pub fn read_u64(data: &[u8], offset: usize) -> Result<u64> {
+    let bytes: [u8; 8] = slice(data, offset, 8)?
+        .try_into()
+        .map_err(|_| Error::Invalid("invalid u64 range".to_owned()))?;
+    Ok(u64::from_le_bytes(bytes))
+}
+
+pub fn read_i64(data: &[u8], offset: usize) -> Result<i64> {
+    let bytes: [u8; 8] = slice(data, offset, 8)?
+        .try_into()
+        .map_err(|_| Error::Invalid("invalid i64 range".to_owned()))?;
+    Ok(i64::from_le_bytes(bytes))
+}
+
+pub fn usize_from_u64(value: u64, field: &str) -> Result<usize> {
+    usize::try_from(value).map_err(|_| Error::Invalid(format!("{field} 0x{value:x} exceeds usize")))
+}
+
+pub fn checked_index(base: usize, index: usize, stride: usize) -> Result<usize> {
+    index
+        .checked_mul(stride)
+        .and_then(|value| base.checked_add(value))
+        .ok_or_else(|| Error::Invalid("table index overflow".to_owned()))
+}
+
+pub fn align_up(value: u64, alignment: u64) -> Result<u64> {
+    if alignment == 0 || !alignment.is_power_of_two() {
+        return invalid(format!("invalid alignment {alignment}"));
+    }
+    value
+        .checked_add(alignment - 1)
+        .map(|aligned| aligned & !(alignment - 1))
+        .ok_or_else(|| Error::Invalid("alignment overflow".to_owned()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn layout(name_index: u32) -> ElfLayout {
+        ElfLayout {
+            entrypoint: 0,
+            program_header_offset: 0,
+            program_header_size: 0x38,
+            program_header_count: 0,
+            program_headers: Vec::new(),
+            section_headers: vec![
+                SectionHeader {
+                    name: 0,
+                    section_type: 0,
+                    flags: 0,
+                    address: 0,
+                    offset: 0,
+                    size: 0,
+                    link: 0,
+                    info: 0,
+                    alignment: 0,
+                    entry_size: 0,
+                },
+                SectionHeader {
+                    name: name_index,
+                    section_type: 1,
+                    flags: 0,
+                    address: 0,
+                    offset: 0,
+                    size: 0,
+                    link: 0,
+                    info: 0,
+                    alignment: 0,
+                    entry_size: 0,
+                },
+                SectionHeader {
+                    name: 1,
+                    section_type: SHT_STRTAB,
+                    flags: 0,
+                    address: 0,
+                    offset: 0,
+                    size: 8,
+                    link: 0,
+                    info: 0,
+                    alignment: 1,
+                    entry_size: 0,
+                },
+            ],
+            section_name_index: 2,
+            private_section_index: usize::MAX,
+        }
+    }
+
+    #[test]
+    fn section_names_resolve_from_elf_string_table() {
+        let names = layout(1)
+            .section_names(b"\0text\0\0\0")
+            .expect("valid names");
+        assert_eq!(names, ["", "text", "text"]);
+    }
+
+    #[test]
+    fn section_names_reject_out_of_range_name_offsets() {
+        let error = layout(8)
+            .section_names(b"\0text\0\0\0")
+            .expect_err("invalid offset");
+        assert!(error.to_string().contains("exceeds section-name table"));
+    }
+
+    #[test]
+    fn section_names_reject_invalid_utf8() {
+        let mut elf_layout = layout(1);
+        elf_layout.section_headers[1].name = 1;
+        let error = elf_layout
+            .section_names(b"\0\xff\0\0\0\0\0\0")
+            .expect_err("invalid UTF-8");
+        assert!(error.to_string().contains("is not UTF-8"));
+    }
+
+    #[test]
+    fn section_names_reject_non_string_table() {
+        let mut elf_layout = layout(1);
+        elf_layout.section_headers[2].section_type = 1;
+        let error = elf_layout
+            .section_names(b"\0text\0\0\0")
+            .expect_err("wrong section type");
+        assert!(error.to_string().contains("unexpected type"));
+    }
+
+    #[test]
+    fn section_names_reject_unterminated_table() {
+        let elf_layout = layout(1);
+        let error = elf_layout
+            .section_names(b"\0text\0\x01\x01")
+            .expect_err("unterminated table");
+        assert!(error.to_string().contains("not NUL terminated"));
+    }
+
+    #[test]
+    fn append_load_segment_updates_program_headers() {
+        let elf_layout = ElfLayout {
+            entrypoint: 0,
+            program_header_offset: 0,
+            program_header_size: 0x38,
+            program_header_count: 0,
+            program_headers: Vec::new(),
+            section_headers: Vec::new(),
+            section_name_index: 0,
+            private_section_index: usize::MAX,
+        };
+        let mut output = vec![0_u8; 0x2000];
+        let updated = elf_layout
+            .append_load_segment(
+                &mut output,
+                LoadSegment {
+                    offset: 0x1000,
+                    virtual_address: 0x2000,
+                    file_size: 0x20,
+                    memory_size: 0x20,
+                    flags: PF_R,
+                    alignment: 0x1000,
+                },
+            )
+            .expect("append segment");
+        assert_eq!(updated.program_header_count, 1);
+        assert_eq!(updated.program_headers[0].virtual_address, 0x2000);
+        assert_eq!(&output[0..4], &PT_LOAD.to_le_bytes());
+        assert_eq!(&output[0x38..0x3a], &1_u16.to_le_bytes());
+    }
+
+    #[test]
+    fn append_load_segment_rejects_program_header_overlap() {
+        let mut elf_layout = ElfLayout {
+            entrypoint: 0,
+            program_header_offset: 0,
+            program_header_size: 0x38,
+            program_header_count: 0,
+            program_headers: Vec::new(),
+            section_headers: Vec::new(),
+            section_name_index: 0,
+            private_section_index: usize::MAX,
+        };
+        elf_layout.section_headers.push(SectionHeader {
+            name: 0,
+            section_type: 1,
+            flags: 0,
+            address: 0,
+            offset: 0x20,
+            size: 1,
+            link: 0,
+            info: 0,
+            alignment: 1,
+            entry_size: 0,
+        });
+        let mut output = vec![0_u8; 0x100];
+        let error = elf_layout
+            .append_load_segment(
+                &mut output,
+                LoadSegment {
+                    offset: 0x80,
+                    virtual_address: 0x1080,
+                    file_size: 0x20,
+                    memory_size: 0x20,
+                    flags: PF_R,
+                    alignment: 0x1000,
+                },
+            )
+            .expect_err("overlapping program header");
+        assert!(error.to_string().contains("additional program header"));
+    }
+}