This ensures that the cwd of the process is within the chroot
environment, improving security for root processes.
The cwd after the chroot is the same as before, this is needed to
start binaries given as relative path name.
Since the recent move of the process creation into core, the original chroot trampoline
mechanism implemented in 'os/src/app/chroot' does not work anymore. A
process could simply escape the chroot environment by spawning a new
process via core's PD service. Therefore, this patch moves the chroot
support into core. So the chroot policy becomes mandatory part of the
process creation. For each process created by core, core checks for
'root' argument of the PD session. If a path is present, core takes the
precautions needed to execute the new process in the specified chroot
environment.
This conceptual change implies minor changes with respect to the Genode
API and the configuration of the init process. The API changes are the
enhancement of the 'Genode::Child' and 'Genode::Process' constructors to
take the root path as argument. Init supports the specification of a
chroot per process by specifying the new 'root' attribute to the
'<start>' node of the process. In line with these changes, the
'Loader::Session::start' function has been enhanced with the additional
(optional) root argument.
On Linux, we use the session label for naming the corresponding Linux
process. When looking up the processes via 'ps', the Genode process
hierarchy becomes immediately visible.
Genode used to create new processes by directly forking from the
respective Genode parent using the process library. The forking process
created a PD session at core merely for propagating the PID of the new
process into core (for later destruction). This traditional mechanisms
has the following disadvantages:
First, the PID reported by the creating process to core cannot easily be
validated by core. Therefore core has to trust the PD client to not
specify a PID of an existing process, which would happen to be killed
once the PD session gets destructed. This problem is documented by
issue #318. Second, there is no way for a Genode process to detect the
failure of its any grandchildren. The immediate parent of a faulting
process could use the SIGCHLD-and-waitpid mechanism to observe its
children but this mechanism does not work transitively.
By performing the process creation exclusively within core, all Genode
processes become immediate child processes of core. Hence, core can
respond to failures of any of those processes and reflect such
conditions via core's session interfaces. Furthermore, the PID
associated to a PD session is locally known within core and cannot be
forged anymore. In fact, there is actually no need at all to make
processes aware of any PIDs of other processes.
Please note that this patch breaks the 'chroot' mechanism that comes in
the form of the 'os/src/app/chroot' program. Because all processes are
forked from core, a chroot'ed process could sneak outside its chroot
environment by just creating a new Genode process. To address this
issue, the chroot mechanism must be added to core.
This patch simplifies the system call bindings. The common syscall
bindings in 'src/platform/' have been reduced to the syscalls needed by
non-core programs. The additional syscalls that are needed solely by
core have been moved to 'src/core/include/core_linux_syscalls.h'.
Furthermore, the resource path is not used outside of core anymore.
Hence, we could get rid of the rpath library. The resource-path code has
been moved to 'src/core/include/resource_path.h'. The IPC-related parts
of 'src/platform' have been moved to the IPC library. So there is now a
clean separation between low-level syscall bindings (in 'src/platform')
and higher-level code.
The code for the socket-descriptor registry is now located in the
'src/base/ipc/socket_descriptor_registry.h' header. The interface is
separated from 'ipc.cc' because core needs to access the registry from
outside the ipc library.
This patch changes the way of how dataspace content is accessed by
processes outside of core. Dataspaces are opened by core only and the
corresponding file descriptors are handed out the other processes via
the 'Linux_dataspace::fd()' RPC function. At the client side, the
returned file descriptor is then used to mmap the file.
Consequently, this patch eliminates all files from 'lx_rpath'. The
path is still needed by core to temporarily create dataspaces and
unix domain sockets. However, those files are unlinked immediately
after their creation.
This patch alleviates the need for any non-core process to create Unix
domain sockets locally. All sockets used for RPC communication are
created by core and subsequently passed to the other processes via RPC
or the parent interface. The immediate benefit is that no process other
than core needs to access the 'rpath' directory in order to communicate.
However, access to 'rpath' is still needed for accessing dataspaces.
Core creates one socket pair per thread on demand on the first call of
the 'Linux_cpu_session::server_sd()' or 'Linux_cpu_session::client_sd()'
functions. 'Linux_cpu_session' is a Linux-specific extension to the CPU
session interface. In addition to the socket accessors, the extension
provides a mechanism to register the PID/TID of a thread. Those
information were formerly propagated into core along with the thread
name as argument to 'create_thread()'.
Because core creates socket pairs for entrypoints, it needs to know all
threads that are potential entrypoints. For lx_hybrid programs, we
hadn't had propagated any thread information into core, yet. Hence, this
patch also contains the code for registering threads of hybrid
applications at core.
This patch introduces the functions 'affinity' and 'num_cpus' to the CPU
session interface. The interface extension will allow the assignment of
individual threads to CPUs. At this point, it is just a stub with no
actual platform support.
This patch extends the RAM session interface with the ability to
allocate DMA buffers. The client specifies the type of RAM dataspace to
allocate via the new 'cached' argument of the 'Ram_session::alloc()'
function. By default, 'cached' is true, which correponds to the common
case and the original behavior. When setting 'cached' to 'false', core
takes the precautions needed to register the memory as uncached in the
page table of each process that has the dataspace attached.
Currently, the support for allocating DMA buffers is implemented for
Fiasco.OC only. On x86 platforms, it is generally not needed. But on
platforms with more relaxed cache coherence (such as ARM), user-level
device drivers should always use uncacheable memory for DMA transactions.
With this patch clients of the RM service can state if they want a mapping
to be executable or not. This allows dataspaces to be mapped as
non-executable on Linux by default and as executable only if needed.
Partially fixes#176.
