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Commit 7a4fb7a4 authored by Bowgo Tsai's avatar Bowgo Tsai
Browse files

first-stage mount: support using other avb_keys 

This change allows specifying additional avb keys to verify a fstab
entry. It can be used together with the original 'avb' flag. When both
'avb' and 'avb_keys' are present, it will try to use avb_keys to verify
this partition and extract the AVB descriptor from the end of it first.
When avb_key fails, it falls back to searching the AVB descriptor in the
built-in /vbmeta (and its chained partitions) with the matched partition
name.

An example of a fstab file:

system  /system  ext4  ro,barrier=1  wait,slotselect,avb=vbmeta,logical,first_stage_mount,avb_keys=/avb/gsi.avbpubkey
vendor  /vendor  ext4  ro,barrier=1  wait,slotselect,avb,logical,first_stage_mount

The overhead of adding an additional 'avb_keys' should not be significant,
as the typical size of a AVB Hashtree descriptor for /system is usually
less than 1000 bytes. e.g., on crosshatch, it's about 600 bytes, which
takes less than 1 millisecond for the following call to return failure.

   auto avb_standalone_handle = AvbHandle::LoadAndVerifyVbmeta(*fstab_entry);

We also checked the time spent on init's first stage on crosshatch, with the
following CL to set ro.boottime.init.first_stage. The testing result
shows no significant difference between them as well.

https://android-review.googlesource.com/c/platform/system/core/+/934536

With an additional avb_keys entry for /system
    [ro.boottime.init.first_stage]: [728]
    [ro.boottime.init.first_stage]: [720]
    [ro.boottime.init.first_stage]: [722]

Without an additional avb_keys entry for /system
    [ro.boottime.init.first_stage]: [730]
    [ro.boottime.init.first_stage]: [728]
    [ro.boottime.init.first_stage]: [725]

Bug: 124491153
Test: boot a device with above fstab settings

Change-Id: I0c81f816efb0dd40c93da2df304f2e215df9d105
Merged-In: I0c81f816efb0dd40c93da2df304f2e215df9d105
(cherry picked from commit a0f8b05d)
parent 83e52ce9

init/first_stage_mount.cpp

+33 −20
Original line number Diff line number Diff line
@@ -80,7 +80,7 @@ class FirstStageMount { 
    bool InitMappedDevice(const std::string& verity_device);

    bool InitDeviceMapper();

    bool CreateLogicalPartitions();

    bool MountPartition(const Fstab::iterator& begin, bool erase_used_fstab_entry,

    bool MountPartition(const Fstab::iterator& begin, bool erase_same_mounts,

                        Fstab::iterator* end = nullptr);



    bool MountPartitions();
@@ -437,21 +437,26 @@ bool FirstStageMount::InitMappedDevice(const std::string& dm_device) { 


    uevent_listener_.RegenerateUeventsForPath(syspath, verity_callback);

    if (!found) {

        LOG(INFO) << "dm-verity device not found in /sys, waiting for its uevent";

        LOG(INFO) << "dm device '" << dm_device << "' not found in /sys, waiting for its uevent";

        Timer t;

        uevent_listener_.Poll(verity_callback, 10s);

        LOG(INFO) << "wait for dm-verity device returned after " << t;

        LOG(INFO) << "wait for dm device '" << dm_device << "' returned after " << t;

    }

    if (!found) {

        LOG(ERROR) << "dm-verity device not found after polling timeout";

        LOG(ERROR) << "dm device '" << dm_device << "' not found after polling timeout";

        return false;

    }



    return true;

}



bool FirstStageMount::MountPartition(const Fstab::iterator& begin, bool erase_used_fstab_entry,

bool FirstStageMount::MountPartition(const Fstab::iterator& begin, bool erase_same_mounts,

                                     Fstab::iterator* end) {

    // Sets end to begin + 1, so we can just return on failure below.

    if (end) {

        *end = begin + 1;

    }



    if (begin->fs_mgr_flags.logical) {

        if (!fs_mgr_update_logical_partition(&(*begin))) {

            return false;
@@ -477,7 +482,7 @@ bool FirstStageMount::MountPartition(const Fstab::iterator& begin, bool erase_us 
            mounted = (fs_mgr_do_mount_one(*current) == 0);

        }

    }

    if (erase_used_fstab_entry) {

    if (erase_same_mounts) {

        current = fstab_.erase(begin, current);

    }

    if (end) {
@@ -494,7 +499,7 @@ bool FirstStageMount::TrySwitchSystemAsRoot() { 
        return entry.mount_point == "/metadata";

    });

    if (metadata_partition != fstab_.end()) {

        if (MountPartition(metadata_partition, true /* erase_used_fstab_entry */)) {

        if (MountPartition(metadata_partition, true /* erase_same_mounts */)) {

            UseGsiIfPresent();

        }

    }
@@ -505,7 +510,7 @@ bool FirstStageMount::TrySwitchSystemAsRoot() { 


    if (system_partition == fstab_.end()) return true;



    if (MountPartition(system_partition, false)) {

    if (MountPartition(system_partition, false /* erase_same_mounts */)) {

        if (gsi_not_on_userdata_ && fs_mgr_verity_is_check_at_most_once(*system_partition)) {

            LOG(ERROR) << "check_most_at_once forbidden on external media";

            return false;
@@ -560,7 +565,7 @@ bool FirstStageMount::MountPartitions() { 
        }



        Fstab::iterator end;

        if (!MountPartition(current, false, &end)) {

        if (!MountPartition(current, false /* erase_same_mounts */, &end)) {

            if (current->fs_mgr_flags.no_fail) {

                LOG(INFO) << "Failed to mount " << current->mount_point

                          << ", ignoring mount for no_fail partition";
@@ -797,11 +802,9 @@ bool FirstStageMountVBootV2::GetDmVerityDevices() { 
bool FirstStageMountVBootV2::SetUpDmVerity(FstabEntry* fstab_entry) {

    AvbHashtreeResult hashtree_result;



    if (fstab_entry->fs_mgr_flags.avb) {

        if (!InitAvbHandle()) return false;

        hashtree_result =

                avb_handle_->SetUpAvbHashtree(fstab_entry, false /* wait_for_verity_dev */);

    } else if (!fstab_entry->avb_keys.empty()) {

    // It's possible for a fstab_entry to have both avb_keys and avb flag.

    // In this case, try avb_keys first, then fallback to avb flag.

    if (!fstab_entry->avb_keys.empty()) {

        if (!InitAvbHandle()) return false;

        // Checks if hashtree should be disabled from the top-level /vbmeta.

        if (avb_handle_->status() == AvbHandleStatus::kHashtreeDisabled ||
@@ -813,14 +816,24 @@ bool FirstStageMountVBootV2::SetUpDmVerity(FstabEntry* fstab_entry) { 
            auto avb_standalone_handle = AvbHandle::LoadAndVerifyVbmeta(*fstab_entry);

            if (!avb_standalone_handle) {

                LOG(ERROR) << "Failed to load offline vbmeta for " << fstab_entry->mount_point;

                return false;

            }

                // Fallbacks to built-in hashtree if fs_mgr_flags.avb is set.

                if (!fstab_entry->fs_mgr_flags.avb) return false;

                LOG(INFO) << "Fallback to built-in hashtree for " << fstab_entry->mount_point;

                hashtree_result =

                        avb_handle_->SetUpAvbHashtree(fstab_entry, false /* wait_for_verity_dev */);

            } else {

                // Sets up hashtree via the standalone handle.

                if (IsStandaloneImageRollback(*avb_handle_, *avb_standalone_handle, *fstab_entry)) {

                    return false;

                }

                hashtree_result = avb_standalone_handle->SetUpAvbHashtree(

                        fstab_entry, false /* wait_for_verity_dev */);

            }

        }

    } else if (fstab_entry->fs_mgr_flags.avb) {

        if (!InitAvbHandle()) return false;

        hashtree_result =

                avb_handle_->SetUpAvbHashtree(fstab_entry, false /* wait_for_verity_dev */);

    } else {

        return true;  // No need AVB, returns true to mount the partition directly.

    }