tock_tbf/parse.rs
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// Licensed under the Apache License, Version 2.0 or the MIT License.
// SPDX-License-Identifier: Apache-2.0 OR MIT
// Copyright Tock Contributors 2022.
//! Tock Binary Format parsing code.
use core::{mem, str};
use crate::types;
/// Parse the TBF header length and the entire length of the TBF binary.
///
/// ## Return
///
/// If all parsing is successful:
/// - Ok((Version, TBF header length, entire TBF length))
///
/// If we cannot parse the header because we have run out of flash, or the
/// values are entirely wrong we return `UnableToParse`. This means we have hit
/// the end of apps in flash.
/// - Err(InitialTbfParseError::UnableToParse)
///
/// Any other error we return an error and the length of the entire app so that
/// we can skip over it and check for the next app.
/// - Err(InitialTbfParseError::InvalidHeader(app_length))
pub fn parse_tbf_header_lengths(
app: &[u8; 8],
) -> Result<(u16, u16, u32), types::InitialTbfParseError> {
// Version is the first 16 bits of the app TBF contents. We need this to
// correctly parse the other lengths.
//
// ## Safety
// We trust that the version number has been checked prior to running this
// parsing code. That is, whatever loaded this application has verified that
// the version is valid and therefore we can trust it.
let version = u16::from_le_bytes([app[0], app[1]]);
match version {
2 => {
// In version 2, the next 16 bits after the version represent
// the size of the TBF header in bytes.
let tbf_header_size = u16::from_le_bytes([app[2], app[3]]);
// The next 4 bytes are the size of the entire app's TBF space
// including the header. This also must be checked before parsing
// this header and we trust the value in flash.
let tbf_size = u32::from_le_bytes([app[4], app[5], app[6], app[7]]);
// Check that the header length isn't greater than the entire app,
// and is at least as large as the v2 required header (which is 16
// bytes). If that at least looks good then return the sizes.
if u32::from(tbf_header_size) > tbf_size || tbf_header_size < 16 {
Err(types::InitialTbfParseError::InvalidHeader(tbf_size))
} else {
Ok((version, tbf_header_size, tbf_size))
}
}
// Since we have to trust the total size, and by extension the version
// number, if we don't know how to handle the version this must not be
// an actual app. Likely this is just the end of the app linked list.
_ => Err(types::InitialTbfParseError::UnableToParse),
}
}
/// Parse a TBF header stored in flash.
///
/// The `header` must be a slice that only contains the TBF header. The caller
/// should use the `parse_tbf_header_lengths()` function to determine this
/// length to create the correct sized slice.
pub fn parse_tbf_header(
header: &'static [u8],
version: u16,
) -> Result<types::TbfHeader, types::TbfParseError> {
match version {
2 => {
// Get the required base. This will succeed because we parsed the
// first bit of the header already in `parse_tbf_header_lengths()`.
let tbf_header_base: types::TbfHeaderV2Base = header.try_into()?;
// Calculate checksum. The checksum is the XOR of each 4 byte word
// in the header.
let mut checksum: u32 = 0;
// Get an iterator across 4 byte fields in the header.
let header_iter = header.chunks_exact(4);
// Iterate all chunks and XOR the chunks to compute the checksum.
for (i, chunk) in header_iter.enumerate() {
let word = u32::from_le_bytes(chunk.try_into()?);
if i == 3 {
// Skip the checksum field.
} else {
checksum ^= word;
}
}
// Verify the header matches.
if checksum != tbf_header_base.checksum {
return Err(types::TbfParseError::ChecksumMismatch(
tbf_header_base.checksum,
checksum,
));
}
// Get the rest of the header. The `remaining` variable will
// continue to hold the remainder of the header we have not
// processed.
let mut remaining = header
.get(16..)
.ok_or(types::TbfParseError::NotEnoughFlash)?;
// If there is nothing left in the header then this is just a
// padding "app" between two other apps.
if remaining.len() == 0 {
// Just padding.
Ok(types::TbfHeader::Padding(tbf_header_base))
} else {
// This is an actual app.
// Places to save fields that we parse out of the header
// options.
let mut main_pointer: Option<types::TbfHeaderV2Main> = None;
let mut program_pointer: Option<types::TbfHeaderV2Program> = None;
let mut wfr_pointer: Option<&'static [u8]> = None;
let mut app_name_str = "";
let mut fixed_address_pointer: Option<&'static [u8]> = None;
let mut permissions_pointer: Option<&'static [u8]> = None;
let mut storage_permissions_pointer: Option<&'static [u8]> = None;
let mut kernel_version: Option<types::TbfHeaderV2KernelVersion> = None;
let mut short_id: Option<types::TbfHeaderV2ShortId> = None;
// Iterate the remainder of the header looking for TLV entries.
while remaining.len() > 0 {
// Get the T and L portions of the next header (if it is
// there).
let tlv_header: types::TbfTlv = remaining
.get(0..4)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?;
remaining = remaining
.get(4..)
.ok_or(types::TbfParseError::NotEnoughFlash)?;
match tlv_header.tipe {
types::TbfHeaderTypes::TbfHeaderMain => {
let entry_len = mem::size_of::<types::TbfHeaderV2Main>();
// If there is already a header do nothing: if this is a second Main
// keep the first one, if it's a Program we ignore the Main
if main_pointer.is_none() {
if tlv_header.length as usize == entry_len {
main_pointer = Some(
remaining
.get(0..entry_len)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?,
);
} else {
return Err(types::TbfParseError::BadTlvEntry(
tlv_header.tipe as usize,
));
}
}
}
types::TbfHeaderTypes::TbfHeaderProgram => {
let entry_len = mem::size_of::<types::TbfHeaderV2Program>();
if program_pointer.is_none() {
if tlv_header.length as usize == entry_len {
program_pointer = Some(
remaining
.get(0..entry_len)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?,
);
} else {
return Err(types::TbfParseError::BadTlvEntry(
tlv_header.tipe as usize,
));
}
}
}
types::TbfHeaderTypes::TbfHeaderWriteableFlashRegions => {
// Length must be a multiple of the size of a region definition.
if tlv_header.length as usize
% mem::size_of::<types::TbfHeaderV2WriteableFlashRegion>()
== 0
{
// Capture a slice with just the wfr information.
let wfr_slice = remaining
.get(0..tlv_header.length as usize)
.ok_or(types::TbfParseError::NotEnoughFlash)?;
wfr_pointer = Some(wfr_slice);
} else {
return Err(types::TbfParseError::BadTlvEntry(
tlv_header.tipe as usize,
));
}
}
types::TbfHeaderTypes::TbfHeaderPackageName => {
let name_buf = remaining
.get(0..tlv_header.length as usize)
.ok_or(types::TbfParseError::NotEnoughFlash)?;
str::from_utf8(name_buf)
.map(|name_str| {
app_name_str = name_str;
})
.or(Err(types::TbfParseError::BadProcessName))?;
}
types::TbfHeaderTypes::TbfHeaderFixedAddresses => {
let entry_len = mem::size_of::<types::TbfHeaderV2FixedAddresses>();
if tlv_header.length as usize == entry_len {
fixed_address_pointer = Some(
remaining
.get(0..entry_len)
.ok_or(types::TbfParseError::NotEnoughFlash)?,
);
} else {
return Err(types::TbfParseError::BadTlvEntry(
tlv_header.tipe as usize,
));
}
}
types::TbfHeaderTypes::TbfHeaderPermissions => {
permissions_pointer = Some(
remaining
.get(0..tlv_header.length as usize)
.ok_or(types::TbfParseError::NotEnoughFlash)?,
);
}
types::TbfHeaderTypes::TbfHeaderStoragePermissions => {
storage_permissions_pointer = Some(
remaining
.get(0..tlv_header.length as usize)
.ok_or(types::TbfParseError::NotEnoughFlash)?,
);
}
types::TbfHeaderTypes::TbfHeaderKernelVersion => {
let entry_len = mem::size_of::<types::TbfHeaderV2KernelVersion>();
if tlv_header.length as usize == entry_len {
kernel_version = Some(
remaining
.get(0..entry_len)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?,
);
} else {
return Err(types::TbfParseError::BadTlvEntry(
tlv_header.tipe as usize,
));
}
}
types::TbfHeaderTypes::TbfHeaderShortId => {
let entry_len = mem::size_of::<types::TbfHeaderV2ShortId>();
if tlv_header.length as usize == entry_len {
short_id = Some(
remaining
.get(0..entry_len)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?,
);
} else {
return Err(types::TbfParseError::BadTlvEntry(
tlv_header.tipe as usize,
));
}
}
_ => {}
}
// All TLV blocks are padded to 4 bytes, so we need to skip
// more if the length is not a multiple of 4.
let skip_len: usize = (tlv_header.length as usize)
.checked_next_multiple_of(4)
.ok_or(types::TbfParseError::InternalError)?;
remaining = remaining
.get(skip_len..)
.ok_or(types::TbfParseError::NotEnoughFlash)?;
}
let tbf_header = types::TbfHeaderV2 {
base: tbf_header_base,
main: main_pointer,
program: program_pointer,
package_name: Some(app_name_str),
writeable_regions: wfr_pointer,
fixed_addresses: fixed_address_pointer,
permissions: permissions_pointer,
storage_permissions: storage_permissions_pointer,
kernel_version,
short_id,
};
Ok(types::TbfHeader::TbfHeaderV2(tbf_header))
}
}
_ => Err(types::TbfParseError::UnsupportedVersion(version)),
}
}
pub fn parse_tbf_footer(
footers: &'static [u8],
) -> Result<(types::TbfFooterV2Credentials, u32), types::TbfParseError> {
let mut remaining = footers;
let tlv_header: types::TbfTlv = remaining
.get(0..4)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?;
remaining = remaining
.get(4..)
.ok_or(types::TbfParseError::NotEnoughFlash)?;
match tlv_header.tipe {
types::TbfHeaderTypes::TbfFooterCredentials => {
let credential: types::TbfFooterV2Credentials = remaining
.get(0..tlv_header.length as usize)
.ok_or(types::TbfParseError::NotEnoughFlash)?
.try_into()?;
// Check length here
let length = tlv_header.length;
Ok((credential, length as u32))
}
_ => Err(types::TbfParseError::BadTlvEntry(tlv_header.tipe as usize)),
}
}