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MigTD: handle target TD without SERVTD_EXT #759

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61 changes: 33 additions & 28 deletions src/migtd/src/mig_policy.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -270,7 +270,7 @@ mod v2 {
init_policy: &[u8],
init_event_log: &[u8],
init_td_report: &[u8],
servtd_ext_src: &[u8],
servtd_ext_src: Option<&[u8]>,
) -> Result<Vec<u8>, PolicyError> {
let policy_issuer_chain = get_policy_issuer_chain().ok_or(PolicyError::InvalidParameter)?;

Expand All @@ -284,34 +284,39 @@ mod v2 {
)?;
let policy = get_verified_policy().ok_or(PolicyError::InvalidParameter)?;

// Verify the td report init / event log init / policy init
let servtd_ext_src_obj =
ServtdExt::read_from_bytes(servtd_ext_src).ok_or(PolicyError::InvalidParameter)?;
let init_tdreport = verify_init_tdreport(init_td_report, &servtd_ext_src_obj)?;
let _engine_svn = policy
.servtd_tcb_mapping
.get_engine_svn_by_measurements(&Measurements::new_from_bytes(
&init_tdreport.td_info.mrtd,
&init_tdreport.td_info.rtmr0,
&init_tdreport.td_info.rtmr1,
None,
None,
))
.ok_or(PolicyError::SvnMismatch)?;
let verified_policy_init = verify_policy_and_event_log(
init_event_log,
init_policy,
policy_issuer_chain,
&get_rtmrs_from_tdreport(&init_tdreport)?,
)?;
// Verify the init TD report only when servtd_ext is available.
// Without servtd_ext (target TD ATTRIBUTES.SERVTDEXT=0), we cannot verify
// the init TD report's servtd_info_hash, so skip init report verification
// entirely and only rely on the current peer TD report verification above.
if let Some(ext_bytes) = servtd_ext_src {
let servtd_ext_src_obj =
ServtdExt::read_from_bytes(ext_bytes).ok_or(PolicyError::InvalidParameter)?;
let init_tdreport = verify_init_tdreport(init_td_report, &servtd_ext_src_obj)?;
let _engine_svn = policy
.servtd_tcb_mapping
.get_engine_svn_by_measurements(&Measurements::new_from_bytes(
&init_tdreport.td_info.mrtd,
&init_tdreport.td_info.rtmr0,
&init_tdreport.td_info.rtmr1,
None,
None,
))
.ok_or(PolicyError::SvnMismatch)?;
let verified_policy_init = verify_policy_and_event_log(
init_event_log,
init_policy,
policy_issuer_chain,
&get_rtmrs_from_tdreport(&init_tdreport)?,
)?;

let relative_reference =
get_init_tcb_evaluation_info(&init_tdreport, &verified_policy_init)?;
policy.policy_data.evaluate_policy_common(
&evaluation_data_src,
&relative_reference,
true,
)?;
let relative_reference =
get_init_tcb_evaluation_info(&init_tdreport, &verified_policy_init)?;
policy.policy_data.evaluate_policy_common(
&evaluation_data_src,
&relative_reference,
true,
)?;
}

// If backward policy exists, evaluate the migration src based on it.
let relative_reference = get_local_tcb_evaluation_info()?;
Expand Down
31 changes: 22 additions & 9 deletions src/migtd/src/migration/rebinding.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -604,7 +604,7 @@ async fn rebinding_old_prepare(
data: &mut Vec<u8>,
remote_policy: Vec<u8>,
) -> Result<(), MigrationResult> {
let servtd_ext = read_servtd_ext(info.binding_handle, &info.target_td_uuid)?;
let servtd_ext = read_servtd_ext(info.binding_handle, &info.target_td_uuid);
let init_policy_hash = digest_sha384(&init_migtd_data.init_policy)?;

// TLS client
Expand All @@ -614,7 +614,7 @@ async fn rebinding_old_prepare(
&init_policy_hash,
&init_migtd_data.init_report,
&init_migtd_data.init_event_log,
&servtd_ext,
servtd_ext.as_ref(),
)
.map_err(|_| {
#[cfg(feature = "vmcall-raw")]
Expand Down Expand Up @@ -677,8 +677,15 @@ async fn rebinding_new_prepare(
// The TLS session is established; we can now extract servtd_ext from the peer certificates.
let servtd_ext = get_servtd_ext_from_cert(&ratls_server.peer_certs())?;
write_rebinding_session_token(&rebind_token.token)?;
write_servtd_rebind_attr(&servtd_ext.cur_servtd_attr)?;
write_approved_servtd_ext_hash(&servtd_ext.calculate_approved_servtd_ext_hash()?)?;
if let Some(ext) = &servtd_ext {
write_servtd_rebind_attr(&ext.cur_servtd_attr)?;
}
write_approved_servtd_ext_hash(
servtd_ext
.map(|ext| ext.calculate_approved_servtd_ext_hash())
.transpose()?
.as_deref(),
)?;

shutdown_transport(ratls_server.transport_mut(), info.mig_request_id).await?;
Ok(())
Expand All @@ -689,7 +696,7 @@ async fn rebinding_new_finalize(
_data: &mut Vec<u8>,
) -> Result<(), MigrationResult> {
write_rebinding_session_token(&[0u8; 32])?;
write_approved_servtd_ext_hash(&[0u8; SHA384_DIGEST_SIZE])?;
write_approved_servtd_ext_hash(Some(&[0u8; SHA384_DIGEST_SIZE]))?;
Ok(())
}

Expand Down Expand Up @@ -733,7 +740,9 @@ pub fn approve_rebinding(
Ok(())
}

fn get_servtd_ext_from_cert(certs: &Option<Vec<&[u8]>>) -> Result<ServtdExt, MigrationResult> {
fn get_servtd_ext_from_cert(
certs: &Option<Vec<&[u8]>>,
) -> Result<Option<ServtdExt>, MigrationResult> {
if let Some(cert_chain) = certs {
if cert_chain.is_empty() {
return Err(MigrationResult::SecureSessionError);
Expand All @@ -748,10 +757,14 @@ fn get_servtd_ext_from_cert(certs: &Option<Vec<&[u8]>>) -> Result<ServtdExt, Mig
.as_ref()
.ok_or(MigrationResult::SecureSessionError)?;

let servtd_ext = find_extension(extensions, &EXTNID_MIGTD_SERVTD_EXT)
.ok_or(MigrationResult::SecureSessionError)?;
let servtd_ext = match find_extension(extensions, &EXTNID_MIGTD_SERVTD_EXT) {
Some(bytes) => bytes,
None => return Ok(None),
};

ServtdExt::read_from_bytes(servtd_ext).ok_or(MigrationResult::InvalidParameter)
ServtdExt::read_from_bytes(servtd_ext)
.ok_or(MigrationResult::InvalidParameter)
.map(Some)
} else {
Err(MigrationResult::SecureSessionError)
}
Expand Down
68 changes: 51 additions & 17 deletions src/migtd/src/migration/servtd_ext.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,11 @@ use tdx_tdcall::tdx::{tdcall_servtd_rd, tdcall_vm_write};

use crate::migration::MigrationResult;

/// Target TD’s ATTRIBUTES field in TDCS (readable via TDG.SERVTD.RD)
pub const TDCS_FIELD_ATTRIBUTES: u64 = 0x1110000300000000;
/// Bit 17 of ATTRIBUTES indicates SERVTD_EXT support
const ATTRIBUTES_SERVTDEXT_BIT: u64 = 1 << 17;

/// SERVTD_EXT_STRUCT fields in target TD’s TDCS
pub const TDCS_FIELD_SERVTD_INIT_SERVTD_INFO_HASH: u64 = 0x191000030000020E;
pub const TDCS_FIELD_SERVTD_INIT_ATTR: u64 = 0x191000030000020D;
Expand Down Expand Up @@ -75,10 +80,25 @@ pub struct TeeModel {
reservtd: [u8; 8],
}

pub fn read_servtd_ext(
binding_handle: u64,
target_td_uuid: &[u64],
) -> Result<ServtdExt, MigrationResult> {
/// Try to read ServtdExt from the target TD's TDCS.
/// Returns `None` if the target TD does not support SERVTD_EXT
/// (i.e., TDCS.ATTRIBUTES.SERVTDEXT bit 17 is zero).
pub fn read_servtd_ext(binding_handle: u64, target_td_uuid: &[u64]) -> Option<ServtdExt> {
// Check TDCS.ATTRIBUTES bit 17 (SERVTDEXT) to determine support.
let attributes = tdcall_servtd_rd(binding_handle, TDCS_FIELD_ATTRIBUTES, target_td_uuid)
.map_err(|e| {
log::error!("Failed to read TDCS.ATTRIBUTES: {e:?}\n");
e
})
.ok()?;
if (attributes.content & ATTRIBUTES_SERVTDEXT_BIT) == 0 {
log::info!(
"Target TD does not support SERVTD_EXT (ATTRIBUTES=0x{:x}).\n",
attributes.content
);
return None;
}

let read_field =
|field_base: u64, elem_size: usize, buf: &mut [u8]| -> Result<(), MigrationResult> {
for (idx, chunk) in buf.chunks_mut(elem_size).enumerate() {
Expand All @@ -99,19 +119,24 @@ pub fn read_servtd_ext(
let mut cur_servtd_info_hash = [0u8; 48];
let mut cur_servtd_attr = [0u8; 8];

read_field(
if read_field(
TDCS_FIELD_SERVTD_INIT_SERVTD_INFO_HASH,
8,
&mut init_servtd_info_hash,
)?;
read_field(TDCS_FIELD_SERVTD_INIT_ATTR, 8, &mut init_attr)?;
read_field(TDCS_FIELD_INIT_CPUSVN, 8, &mut init_cpusvn)?;
read_field(TDCS_FIELD_INIT_TEE_TCB_SVN, 8, &mut init_tee_tcb_svn)?;
read_field(TDCS_FIELD_INIT_TEE_MODEL, 4, &mut init_tee_model)?;
read_field(TDCS_FIELD_SERVTD_INFO_HASH, 8, &mut cur_servtd_info_hash)?;
read_field(TDCS_FIELD_SERVTD_ATTR, 8, &mut cur_servtd_attr)?;

Ok(ServtdExt {
)
.is_err()
|| read_field(TDCS_FIELD_SERVTD_INIT_ATTR, 8, &mut init_attr).is_err()
|| read_field(TDCS_FIELD_INIT_CPUSVN, 8, &mut init_cpusvn).is_err()
|| read_field(TDCS_FIELD_INIT_TEE_TCB_SVN, 8, &mut init_tee_tcb_svn).is_err()
|| read_field(TDCS_FIELD_INIT_TEE_MODEL, 4, &mut init_tee_model).is_err()
|| read_field(TDCS_FIELD_SERVTD_INFO_HASH, 8, &mut cur_servtd_info_hash).is_err()
|| read_field(TDCS_FIELD_SERVTD_ATTR, 8, &mut cur_servtd_attr).is_err()
{
log::error!("Failed to read SERVTD_EXT fields.\n");
return None;
}

Some(ServtdExt {
init_servtd_info_hash,
init_attr,
init_cpusvn,
Expand All @@ -124,12 +149,20 @@ pub fn read_servtd_ext(
})
}

pub fn write_approved_servtd_ext_hash(servtd_ext_hash: &[u8]) -> Result<(), MigrationResult> {
if servtd_ext_hash.len() != SHA384_DIGEST_SIZE {
/// Write the approved SERVTD_EXT hash to the target TD's TDCS.
/// If `servtd_ext_hash` is `None`, this is a no-op (target TD does not support SERVTD_EXT).
pub fn write_approved_servtd_ext_hash(
servtd_ext_hash: Option<&[u8]>,
) -> Result<(), MigrationResult> {
let hash = match servtd_ext_hash {
Some(h) => h,
None => return Ok(()),
};
if hash.len() != SHA384_DIGEST_SIZE {
return Err(MigrationResult::InvalidParameter);
}

for (idx, chunk) in servtd_ext_hash.chunks_exact(size_of::<u64>()).enumerate() {
for (idx, chunk) in hash.chunks_exact(size_of::<u64>()).enumerate() {
let elem = u64::from_le_bytes(chunk.try_into().unwrap());
tdcall_vm_write(
TDCS_FIELD_SERVTD_ACCEPT_SERVTD_EXT_HASH + idx as u64,
Expand All @@ -141,6 +174,7 @@ pub fn write_approved_servtd_ext_hash(servtd_ext_hash: &[u8]) -> Result<(), Migr
Ok(())
}

#[cfg(test)]
mod test {
use super::ServtdExt;

Expand Down
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