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cli/ota: Merge property and kernel cmdline descriptors from child into parent

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Some devices use the legacy Android/ChromiumOS-specific `dm=` kernel
command line option to configure dm-verity without userspace helpers.
These options are specified in kernel command line descriptors in the
system partition's vbmeta header, which need to be merged into the
parent vbmeta image for the bootloader to see them.

This commit adds support for merging property descriptors and kernel
command line descriptors. Property descriptors are merged based on an
exact string match of the property key. Kernel command line descriptors
are merged based on the (non-empty) text before the first equal sign.

Issue: #203

Signed-off-by: Andrew Gunnerson <accounts+github@chiller3.com>
This commit is contained in:
Andrew Gunnerson
2023-11-15 17:52:12 -05:00
parent a9a6107043
commit 935a86e72c
1 changed files with 124 additions and 42 deletions
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avbroot/src/cli/ota.rs
+124 -42
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@@ -400,6 +400,128 @@ fn get_vbmeta_patch_order(
Ok(order)
}
/// Copy the hash or hashtree descriptor from the child image header into the
/// parent image header if the child is unsigned or update the parent's chain
/// descriptor if the child is signed. The existing descriptor in the parent
/// must have the same type as the child.
fn update_security_descriptors(
parent_header: &mut Header,
child_header: &Header,
parent_name: &str,
child_name: &str,
) -> Result<()> {
// This can't fail since the descriptor must have existed for the dependency
// to exist.
let parent_descriptor = parent_header
.descriptors
.iter_mut()
.find(|d| d.partition_name() == Some(child_name))
.unwrap();
let parent_type = parent_descriptor.type_name();
if child_header.public_key.is_empty() {
// vbmeta is unsigned. Copy the child's existing descriptor.
let Some(child_descriptor) = child_header
.descriptors
.iter()
.find(|d| d.partition_name() == Some(child_name))
else {
bail!("{child_name} has no descriptor for itself");
};
let child_type = child_descriptor.type_name();
match (parent_descriptor, child_descriptor) {
(Descriptor::Hash(pd), Descriptor::Hash(cd)) => {
*pd = cd.clone();
}
(Descriptor::HashTree(pd), Descriptor::HashTree(cd)) => {
*pd = cd.clone();
}
_ => {
bail!("{child_name} descriptor ({child_type}) does not match entry in {parent_name} ({parent_type})");
}
}
} else {
// vbmeta is signed; Use a chain descriptor.
match parent_descriptor {
Descriptor::ChainPartition(pd) => {
pd.public_key = child_header.public_key.clone();
}
_ => {
bail!("{child_name} descriptor ({parent_type}) in {parent_name} must be a chain descriptor");
}
}
}
Ok(())
}
/// Get the text before the first equal sign in the kernel command line if it is
/// not empty.
fn cmdline_prefix(cmdline: &str) -> Option<&str> {
let Some((prefix, _)) = cmdline.split_once('=') else {
return None;
};
if prefix.is_empty() {
return None;
}
Some(prefix)
}
/// Merge property descriptors and kernel command line descriptors from the
/// child into the parent. The property descriptors are matched based on the
/// entire property key. The kernel command line descriptors are matched based
/// on the non-empty text left of the first equal sign (if it exists).
///
/// This is a no-op if the child is signed because it is expected to be chain
/// loaded by the parent.
fn update_metadata_descriptors(parent_header: &mut Header, child_header: &Header) {
if !child_header.public_key.is_empty() {
return;
}
for child_descriptor in &child_header.descriptors {
match child_descriptor {
Descriptor::Property(cd) => {
let parent_property = parent_header.descriptors.iter_mut().find_map(|d| match d {
Descriptor::Property(p) if p.key == cd.key => Some(p),
_ => None,
});
if let Some(pd) = parent_property {
pd.value = cd.value.clone();
} else {
parent_header
.descriptors
.push(Descriptor::Property(cd.clone()));
}
}
Descriptor::KernelCmdline(cd) => {
let Some(prefix) = cmdline_prefix(&cd.cmdline) else {
continue;
};
let parent_property = parent_header.descriptors.iter_mut().find_map(|d| match d {
Descriptor::KernelCmdline(p) if cmdline_prefix(&p.cmdline) == Some(prefix) => {
Some(p)
}
_ => None,
});
if let Some(pd) = parent_property {
pd.cmdline = cd.cmdline.clone();
} else {
parent_header
.descriptors
.push(Descriptor::KernelCmdline(cd.clone()));
}
}
_ => {}
}
}
}
/// Update vbmeta headers.
///
/// * If [`Header::flags`] is non-zero, then an error is returned because the
@@ -438,52 +560,12 @@ fn update_vbmeta_headers(
}
for dep in deps.iter() {
// This can't fail since the descriptor must have existed for the
// dependency to exist.
let parent_descriptor = parent_header
.descriptors
.iter_mut()
.find(|d| d.partition_name() == Some(dep))
.unwrap();
let reader = images.get_mut(dep).unwrap();
let (header, _, _) = avb::load_image(reader)
.with_context(|| format!("Failed to load vbmeta footer from image: {dep}"))?;
let pd_type = parent_descriptor.type_name();
if header.public_key.is_empty() {
// vbmeta is unsigned. Use the existing descriptor.
let Some(descriptor) = header
.descriptors
.iter()
.find(|d| d.partition_name() == Some(dep))
else {
bail!("{name} has no descriptor for itself");
};
let d_type = descriptor.type_name();
match (parent_descriptor, descriptor) {
(Descriptor::Hash(pd), Descriptor::Hash(d)) => {
*pd = d.clone();
}
(Descriptor::HashTree(pd), Descriptor::HashTree(d)) => {
*pd = d.clone();
}
_ => {
bail!("{dep} descriptor ({d_type}) does not match entry in {name} ({pd_type})");
}
}
} else {
// vbmeta is signed; Use a chain descriptor.
match parent_descriptor {
Descriptor::ChainPartition(d) => {
d.public_key = header.public_key;
}
_ => {
bail!("{dep} descriptor ({pd_type}) in {name} must be a chain descriptor");
}
}
}
update_security_descriptors(parent_header, &header, name, dep)?;
update_metadata_descriptors(parent_header, &header);
}
// Only sign and rewrite the image if we need to. Some vbmeta images may