pvmfw: avb: Improve access to signed kernel footer
Check that the computed offset is actually a valid index into the slice.
Introduce a helper to get the footer offset, for re-use.
Test: m libpvmfw_avb.integration_test
Change-Id: I20040eb3e2254e9938a31c793ecae481e35b4ad5
diff --git a/pvmfw/avb/tests/utils.rs b/pvmfw/avb/tests/utils.rs
index cf37fcf..e989579 100644
--- a/pvmfw/avb/tests/utils.rs
+++ b/pvmfw/avb/tests/utils.rs
@@ -72,8 +72,14 @@
Ok(fs::read(PUBLIC_KEY_RSA4096_PATH)?)
}
+pub fn get_avb_footer_offset(signed_kernel: &[u8]) -> Result<usize> {
+ let offset = signed_kernel.len().checked_sub(size_of::<AvbFooter>());
+
+ offset.ok_or_else(|| anyhow!("Kernel too small to be AVB-signed"))
+}
+
pub fn extract_avb_footer(kernel: &[u8]) -> Result<AvbFooter> {
- let footer_start = kernel.len() - size_of::<AvbFooter>();
+ let footer_start = get_avb_footer_offset(kernel)?;
// SAFETY: The slice is the same size as the struct which only contains simple data types.
let mut footer = unsafe {
transmute::<[u8; size_of::<AvbFooter>()], AvbFooter>(kernel[footer_start..].try_into()?)