avb: Bump hashtree and FEC size limits to accommodate 8 GiB images

Fixes: #291

Signed-off-by: Andrew Gunnerson <[email protected]>

avbroot/src/format/avb.rs

@@ -51,12 +51,29 @@ pub const FOOTER_MAGIC: [u8; 4] = *b"AVBf";
 pub const HEADER_MAX_SIZE: u64 = 64 * 1024;
 
 /// Maximum hash tree size. The current limit equals the hash tree size for a
-/// 4GiB image using SHA512 digests and a block size of 4096.
-pub const HASH_TREE_MAX_SIZE: u64 = 68_177_920;
-
-/// Maximum FEC data size. The current limit equals the FEC data size for a 4GiB
-/// image using 2 parity bytes per codeword.
-pub const FEC_DATA_MAX_SIZE: u64 = 33_959_936;
+/// 8GiB image using SHA256 digests and a block size of 4096. This is equal to:
+///
+/// ```rust
+/// use avbroot::format::hashtree::HashTree;
+/// let size = HashTree::new(4096, &ring::digest::SHA256, b"")
+///     .compute_level_offsets(8 * 1024 * 1024 * 1024)
+///     .unwrap()
+///    .first()
+///    .map(|r| r.end)
+///    .unwrap_or(0);
+/// ```
+pub const HASH_TREE_MAX_SIZE: u64 = 67_637_248;
+
+/// Maximum FEC data size. The current limit equals the FEC data size for a 8GiB
+/// image using 2 parity bytes per codeword. This is equal to:
+///
+/// ```rust
+/// use avbroot::format::fec::Fec;
+/// let size = Fec::new(8 * 1024 * 1024 * 1024, 4096, 2)
+///     .unwrap()
+///     .fec_size();
+/// ```
+pub const FEC_DATA_MAX_SIZE: u64 = 67_911_680;
 
 #[derive(Debug, Error)]
 pub enum Error {

avbroot/src/format/fec.rs

@@ -196,7 +196,7 @@ impl Fec {
 
     /// Get the size of the FEC data needed to cover the entire file.
     #[inline]
-    fn fec_size(&self) -> usize {
+    pub fn fec_size(&self) -> usize {
         usize::from(self.parity()) * self.rounds as usize * self.block_size as usize
     }
 

avbroot/src/format/hashtree.rs

@@ -72,7 +72,7 @@ impl HashTree {
     /// tree data. The items are returned with the bottom level's offsets first
     /// in the list. Note that the bottom level is stored at the end of the hash
     /// tree data.
-    fn compute_level_offsets(&self, image_size: u64) -> Result<Vec<Range<usize>>> {
+    pub fn compute_level_offsets(&self, image_size: u64) -> Result<Vec<Range<usize>>> {
         let algorithm = self.salted_context.algorithm();
         let digest_size = algorithm.output_len().next_power_of_two();
         let mut ranges = vec![];