Merge "Use /bootstrap-apex for bootstrap APEXes" into main (58ba0b44) · Commits · e / os / android_system_core

init/builtins.cpp

+50 −0

Original line number	Diff line number	Diff line
		@@ -1262,6 +1262,51 @@ static Result<void> MountLinkerConfigForDefaultNamespace() {

		return {};
		}

		static Result<void> MountApexRootForDefaultNamespace() {
		auto mount_namespace_id = GetCurrentMountNamespace();
		if (!mount_namespace_id.ok()) {
		return mount_namespace_id.error();
		}
		// There's nothing to do if it's still in the bootstrap mount namespace.
		// This happens when we don't need to update APEXes (e.g. Microdroid)
		// where bootstrap mount namespace == default mount namespace.
		if (mount_namespace_id.value() == NS_BOOTSTRAP) {
		return {};
		}

		// Now, we're in the "default" mount namespace and need a fresh /apex for
		// the default mount namespace.
		//
		// At this point, there are two mounts at the same mount point: /apex
		// - to tmpfs (private)
		// - to /bootstrap-apex (shared)
		//
		// We need unmount the second mount so that /apex in the default mount
		// namespace becomes RW/empty and "private" (we don't want mount events to
		// propagate to the bootstrap mount namespace).
		//
		// Likewise, we don't want the unmount event itself to propagate to the
		// bootstrap mount namespace. Otherwise, /apex in the bootstrap mount
		// namespace would become empty due to the unmount.
		//
		// Hence, before unmounting, we make /apex (the second one) "private" first.
		// so that the unmouting below doesn't affect to the bootstrap mount namespace.
		if (mount(nullptr, "/apex", nullptr, MS_PRIVATE \| MS_REC, nullptr) == -1) {
		return ErrnoError() << "Failed to remount /apex as private";
		}

		// Now we can unmount /apex (bind-mount to /bootstrap-apex). This only affects
		// in the default mount namespace and /apex is now seen as tmpfs mount.
		// Note that /apex in the bootstrap mount namespace is still a bind-mount to
		// /bootstrap-apex and holds the APEX mounts.
		if (umount2("/apex", MNT_DETACH) == -1) {
		return ErrnoError() << "Failed to umount /apex";
		}

		return {};
		}

		static Result<void> do_update_linker_config(const BuiltinArguments&) {
		return GenerateLinkerConfiguration();
		}
		@@ -1315,6 +1360,11 @@ static Result<void> do_enter_default_mount_ns(const BuiltinArguments& args) {
		if (auto result = SwitchToMountNamespaceIfNeeded(NS_DEFAULT); !result.ok()) {
		return result.error();
		}

		if (auto result = MountApexRootForDefaultNamespace(); !result.ok()) {
		return result.error();
		}

		if (auto result = MountLinkerConfigForDefaultNamespace(); !result.ok()) {
		return result.error();
		}

init/init.cpp

+6 −0

Original line number	Diff line number	Diff line
		@@ -832,6 +832,12 @@ static void MountExtraFilesystems() {
		CHECKCALL(mount("tmpfs", "/apex", "tmpfs", MS_NOEXEC \| MS_NOSUID \| MS_NODEV,
		"mode=0755,uid=0,gid=0"));

		if (NeedsTwoMountNamespaces()) {
		// /bootstrap-apex is used to mount "bootstrap" APEXes.
		CHECKCALL(mount("tmpfs", "/bootstrap-apex", "tmpfs", MS_NOEXEC \| MS_NOSUID \| MS_NODEV,
		"mode=0755,uid=0,gid=0"));
		}

		// /linkerconfig is used to keep generated linker configuration
		CHECKCALL(mount("tmpfs", "/linkerconfig", "tmpfs", MS_NOEXEC \| MS_NOSUID \| MS_NODEV,
		"mode=0755,uid=0,gid=0"));

init/mount_namespace.cpp

+30 −9

Original line number	Diff line number	Diff line
		@@ -66,15 +66,6 @@ static std::string GetMountNamespaceId() {
		return ret;
		}

		// In case we have two sets of APEXes (non-updatable, updatable), we need two separate mount
		// namespaces.
		static bool NeedsTwoMountNamespaces() {
		if (IsRecoveryMode()) return false;
		// In microdroid, there's only one set of APEXes in built-in directories include block devices.
		if (IsMicrodroid()) return false;
		return true;
		}

		static android::base::unique_fd bootstrap_ns_fd;
		static android::base::unique_fd default_ns_fd;

		@@ -83,6 +74,15 @@ static std::string default_ns_id;

		} // namespace

		// In case we have two sets of APEXes (non-updatable, updatable), we need two separate mount
		// namespaces.
		bool NeedsTwoMountNamespaces() {
		if (IsRecoveryMode()) return false;
		// In microdroid, there's only one set of APEXes in built-in directories include block devices.
		if (IsMicrodroid()) return false;
		return true;
		}

		bool SetupMountNamespaces() {
		// Set the propagation type of / as shared so that any mounting event (e.g.
		// /data) is by default visible to all processes. When private mounting is
		@@ -96,6 +96,27 @@ bool SetupMountNamespaces() {
		// the bootstrap namespace get APEXes from the read-only partition.
		if (!(ChangeMount("/apex", MS_PRIVATE))) return false;

		// However, some components (e.g. servicemanager) need to access bootstrap
		// APEXes from the default mount namespace. To achieve that, we bind-mount
		// /apex with /bootstrap-apex (not private) in the bootstrap mount namespace.
		// Bootstrap APEXes are mounted in /apex and also visible in /bootstrap-apex.
		// In the default mount namespace, we detach /bootstrap-apex from /apex and
		// bootstrap APEXes are still be visible in /bootstrap-apex.
		//
		// The end result will look like:
		// in the bootstrap mount namespace:
		// /apex (== /bootstrap-apex)
		// {bootstrap APEXes from the read-only partition}
		//
		// in the default mount namespace:
		// /bootstrap-apex
		// {bootstrap APEXes from the read-only partition}
		// /apex
		// {APEXes, can be from /data partition}
		if (NeedsTwoMountNamespaces()) {
		if (!(BindMount("/bootstrap-apex", "/apex"))) return false;
		}

		// /linkerconfig is a private mountpoint to give a different linker configuration
		// based on the mount namespace. Subdirectory will be bind-mounted based on current mount
		// namespace

init/mount_namespace.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -24,9 +24,12 @@ namespace init {
		enum MountNamespace { NS_BOOTSTRAP, NS_DEFAULT };

		bool SetupMountNamespaces();

		base::Result<void> SwitchToMountNamespaceIfNeeded(MountNamespace target_mount_namespace);

		base::Result<MountNamespace> GetCurrentMountNamespace();

		bool NeedsTwoMountNamespaces();

		} // namespace init
		} // namespace android

init/selinux.cpp

+1 −1

Original line number	Diff line number	Diff line
		@@ -766,7 +766,7 @@ void SelinuxRestoreContext() {
		selinux_android_restorecon("/dev/device-mapper", 0);

		selinux_android_restorecon("/apex", 0);

		selinux_android_restorecon("/bootstrap-apex", 0);
		selinux_android_restorecon("/linkerconfig", 0);

		// adb remount, snapshot-based updates, and DSUs all create files during