Calculate end of bootloader to update SHA256

CHANGELOG.md

@@ -13,6 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Update the app image SHA in the correct location for padded images (#715)
+
 ### Removed
 
 ## [3.3.0] - 2025-01-13

espflash/Cargo.toml

@@ -43,7 +43,7 @@ directories = { version = "5.0.1", optional = true }
 env_logger = { version = "0.11.6", optional = true }
 esp-idf-part = "0.5.0"
 flate2 = "1.0.35"
-hex = { version = "0.4.3", features = ["serde"], optional = true }
+hex = { version = "0.4.3", features = ["serde"]}
 indicatif = { version = "0.17.9", optional = true }
 lazy_static = { version = "1.5.0", optional = true }
 log = "0.4.22"
@@ -79,7 +79,6 @@ cli = [
     "dep:dialoguer",
     "dep:directories",
     "dep:env_logger",
-    "dep:hex",
     "dep:indicatif",
     "dep:lazy_static",
     "dep:parse_int",

espflash/src/image_format.rs

@@ -4,6 +4,7 @@ use std::{borrow::Cow, io::Write, iter::once, mem::size_of};
 
 use bytemuck::{bytes_of, from_bytes, Pod, Zeroable};
 use esp_idf_part::{Partition, PartitionTable, Type};
+use log::debug;
 use sha2::{Digest, Sha256};
 
 use crate::{
@@ -135,11 +136,22 @@ impl<'a> IdfBootloaderFormat<'a> {
         };
 
         // fetch the generated header from the bootloader
-        let mut header: ImageHeader = *from_bytes(&bootloader[0..size_of::<ImageHeader>()]);
+        let mut calc_bootloader_size = 0;
+        let bootloader_header_size = size_of::<ImageHeader>();
+        calc_bootloader_size += bootloader_header_size;
+        let mut header: ImageHeader = *from_bytes(&bootloader[0..bootloader_header_size]);
         if header.magic != ESP_MAGIC {
             return Err(Error::InvalidBootloader);
         }
 
+        for _ in 0..header.segment_count {
+            let segment: SegmentHeader = *from_bytes(
+                &bootloader
+                    [calc_bootloader_size..calc_bootloader_size + size_of::<SegmentHeader>()],
+            );
+            calc_bootloader_size += segment.length as usize + size_of::<SegmentHeader>();
+        }
+
         // update the header if a user has specified any custom arguments
         if let Some(mode) = flash_settings.mode {
             header.flash_mode = mode as u8;
@@ -156,12 +168,26 @@ impl<'a> IdfBootloaderFormat<'a> {
             bytes_of(&header).iter().copied(),
         );
 
-        // re-calculate hash of the bootloader - needed since we modified the header
-        let bootloader_len = bootloader.len();
+        // The header was modified so we need to recalculate the hash of the
+        // bootloader. The hash is at the end of the bootloader segments and
+        // 1-byte checksum at the end of a 16-byte padded boundary.
+        //
+        // Source: Point 3 of https://docs.espressif.com/projects/esp-idf/en/v5.4/esp32c3/api-reference/system/app_image_format.html
+        calc_bootloader_size += 1; // add checksum size
+        calc_bootloader_size = calc_bootloader_size + ((16 - (calc_bootloader_size % 16)) % 16);
+        let bootloader_sha_start = calc_bootloader_size;
+        calc_bootloader_size += 32; // add sha256 size
+        let bootloader_sha_end = calc_bootloader_size;
+
         let mut hasher = Sha256::new();
-        hasher.update(&bootloader[..bootloader_len - 32]);
+        hasher.update(&bootloader[..bootloader_sha_start]);
         let hash = hasher.finalize();
-        bootloader.to_mut()[bootloader_len - 32..].copy_from_slice(&hash);
+        debug!(
+            "Updating bootloader SHA256 from {} to {}",
+            hex::encode(&bootloader[bootloader_sha_start..bootloader_sha_end]),
+            hex::encode(hash)
+        );
+        bootloader.to_mut()[bootloader_sha_start..bootloader_sha_end].copy_from_slice(&hash);
 
         // write the header of the app
         // use the same settings as the bootloader