Hi all,
I'm trying to start new child components from ELF binaries received at run-time and stored in a server-local buffer. Basically, I am trying to implement a server that can receive task descriptions and matching binaries and then start them at run-time (disregarding security concerns for the moment).
It appears, however, that all ROM connections must reference binaries that are available at boot-time and adding to the ROM FS is not possible without accessing Genode's internal code which I'd like to avoid.
So, how would I best go about creating entirely new ROM sessions at runtime?
Best regards, Georg
Hello Georg,
On Thu, Jan 14, 2016 at 12:29:49PM +0100, Georg Guba wrote:
I'm trying to start new child components from ELF binaries received at run-time and stored in a server-local buffer. Basically, I am trying to implement a server that can receive task descriptions and matching binaries and then start them at run-time (disregarding security concerns for the moment).
It appears, however, that all ROM connections must reference binaries that are available at boot-time and adding to the ROM FS is not possible without accessing Genode's internal code which I'd like to avoid.
So, how would I best go about creating entirely new ROM sessions at runtime?
The first idea that comes to my mind is: Implement a ROM server "elf_rom", which stores the retrieved ELF binaries in dataspaces allocated from its RAM session. Afterwards setup the routing in your init config for all "children" of your "parent" to "elf_rom" like follows
<route> .. <service name="ROM"> <child name="elf_rom_server"/> </service> .. </route>
This may need two special precautions. First, you may need a nested init instance which is configured with the route above. Second, you may need some exceptions from the rule above if elf_rom_server does not provide ROMs for "parent" and its shared libraries (if used) like
<service name="ROM" label="parent"> <parent/> </service>
Greets
Hi Georg,
On Thu, Jan 14, 2016 at 12:29:49PM +0100, Georg Guba wrote:
I'm trying to start new child components from ELF binaries received at run-time and stored in a server-local buffer. Basically, I am trying to implement a server that can receive task descriptions and matching binaries and then start them at run-time (disregarding security concerns for the moment).
On 14.01.2016 17:06, Christian Helmuth wrote:
The first idea that comes to my mind is: Implement a ROM server "elf_rom", which stores the retrieved ELF binaries in dataspaces allocated from its RAM session.
As long as your executable binary is statically linked, the problem can be solved in an easier way: When creating a subsystem by constructing a 'Child' object, you have to pass a dataspace capability for the ELF binary. You can simply allocate a new RAM dataspace (i.e., creating an 'Attached_ram_dataspace'), copy the ELF binary into the dataspace and pass the dataspace capability to the constructor of the 'Child'. There is no need to create a ROM server.
However, if you want to start dynamically linked executables, the child component will initially start the dynamic linker, which, in turn, requests the executable binary along with the needed shared libraries as ROM sessions. Your server would need to respond to those requests by handing out ROM-session capabilities. As an example for this approach, I recommend you to look at the loader [1], which seems to be similar to the server you are building.
[1] https://github.com/genodelabs/genode/tree/master/repos/os/src/server/loader
Cheers Norman
Hi Norman and Christian,
thank you both for your answers! I actually got Norman's approach working using a slightly modified version of the demo's launchpad. With this launchpad, all I have to do is load incoming binaries into an Attached_ram_dataspace as Norman said.
diff --git a/repos/demo/include/launchpad/launchpad.h b/repos/demo/include/launchpad/launchpad.h index 9aa0ed5..2e319f8 100644 --- a/repos/demo/include/launchpad/launchpad.h +++ b/repos/demo/include/launchpad/launchpad.h @@ -268,7 +268,9 @@ class Launchpad Genode::Allocator *alloc) { }
Launchpad_child *start_child(const char *prg_name, unsigned long quota, - Genode::Dataspace_capability config_ds); + Genode::Dataspace_capability config_ds, + Genode::Dataspace_capability binary_ds = + Genode::Dataspace_capability());
/** * Exit child and close all its sessions diff --git a/repos/demo/src/lib/launchpad/launchpad.cc b/repos/demo/src/lib/launchpad/launchpad.cc index d60ad51..2fde521 100644 --- a/repos/demo/src/lib/launchpad/launchpad.cc +++ b/repos/demo/src/lib/launchpad/launchpad.cc @@ -186,7 +186,8 @@ void Launchpad::process_config()
Launchpad_child *Launchpad::start_child(const char *filename, unsigned long ram_quota, - Genode::Dataspace_capability config_ds) + Genode::Dataspace_capability config_ds, + Genode::Dataspace_capability binary_ds) { printf("starting %s with quota %lu\n", filename, ram_quota);
@@ -212,19 +213,27 @@ Launchpad_child *Launchpad::start_child(const char *filename, /* lookup executable elf binary */ Dataspace_capability file_cap; Rom_session_capability rom_cap; - try { - /* - * When creating a ROM connection for a non-existing file, the - * constructor of 'Rom_connection' throws a 'Parent::Service_denied' - * exception. - */ - Rom_connection rom(filename, unique_name); - rom.on_destruction(Rom_connection::KEEP_OPEN); - rom_cap = rom.cap(); - file_cap = rom.dataspace(); - } catch (...) { - printf("Error: Could not access file "%s" from ROM service.\n", filename); - return 0; + if (binary_ds == Genode::Dataspace_capability()) + { + /* invalid dataspace, look up in file */ + try { + /* + * When creating a ROM connection for a non-existing file, the + * constructor of 'Rom_connection' throws a 'Parent::Service_denied' + * exception. + */ + Rom_connection rom(filename, unique_name); + rom.on_destruction(Rom_connection::KEEP_OPEN); + rom_cap = rom.cap(); + file_cap = rom.dataspace(); + } catch (...) { + printf("Error: Could not access file "%s" from ROM service.\n", filename); + return 0; + } + } + else + { + file_cap = binary_ds; }
/* create ram session for child with some of our own quota */
On 14 January 2016 at 18:11, Norman Feske <norman.feske@...1...> wrote:
Hi Georg,
On Thu, Jan 14, 2016 at 12:29:49PM +0100, Georg Guba wrote:
I'm trying to start new child components from ELF binaries received at run-time and stored in a server-local buffer. Basically, I am trying to implement a server that can receive task descriptions and matching
binaries
and then start them at run-time (disregarding security concerns for the moment).
On 14.01.2016 17:06, Christian Helmuth wrote:
The first idea that comes to my mind is: Implement a ROM server "elf_rom", which stores the retrieved ELF binaries in dataspaces allocated from its RAM session.
As long as your executable binary is statically linked, the problem can be solved in an easier way: When creating a subsystem by constructing a 'Child' object, you have to pass a dataspace capability for the ELF binary. You can simply allocate a new RAM dataspace (i.e., creating an 'Attached_ram_dataspace'), copy the ELF binary into the dataspace and pass the dataspace capability to the constructor of the 'Child'. There is no need to create a ROM server.
However, if you want to start dynamically linked executables, the child component will initially start the dynamic linker, which, in turn, requests the executable binary along with the needed shared libraries as ROM sessions. Your server would need to respond to those requests by handing out ROM-session capabilities. As an example for this approach, I recommend you to look at the loader [1], which seems to be similar to the server you are building.
[1] https://github.com/genodelabs/genode/tree/master/repos/os/src/server/loader
Cheers Norman
-- Dr.-Ing. Norman Feske Genode Labs
http://www.genode-labs.com · http://genode.org
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