Giving components access to the "next" vDSO

Adam Barth

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Oct 13, 2021, 1:24:17 PM10/13/21

to component-framework-dev, Travis Geiselbrecht, Carlos Pizano, Nick Maniscalco

Hi cf-dev,

As of https://fuchsia.googlesource.com/fuchsia/+/de32eb53e254846244cee17676d1c46207ecf3dd, Zircon now has two vDSOs: stable and next. Currently, every process created by the ELF runner is given the stable vDSO, which contains all the syscalls we know and love.

In addition to the stable syscalls, the next vDSO will also contain in-development syscalls that the Zircon team is iterating on with their customers. In order to make iterating on these syscalls easier, these syscalls are not published in SDK headers and are not accessible to most components.

In order to make it possible to access these syscalls, I'd like to add a policy knob to the program block for the ELF runner, similar to job_policy_ambient_mark_vmo_exec and job_policy_create_raw_processes. For example, we might call the key something like "use_next_vdso".

My next step is to work up a CL to see what's involved in adding this feature to ELF runner. Please let me know if you have any questions or concerns.

Adam

Bryan Henry

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Oct 13, 2021, 2:05:27 PM10/13/21

to Adam Barth, component-framework-dev, Travis Geiselbrecht, Carlos Pizano, Nick Maniscalco

Neat. It should be a pretty simple change. The ELF runner uses process_builder through fuchsia.process.Launcher, even when component_manager is hosting that service, so that component_manager can support running as a v1 component. process_builder already supports using a non-default VDSO if one is provided using HandleType::VdsoVmo, so it should just be a matter of providing ElfRunner::configure_launcher (in src/sys/component_manager/src/elf_runner/mod.rs) that extra handle to add to handle_infos.

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Adam Barth

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Oct 13, 2021, 2:58:52 PM10/13/21

to Bryan Henry, component-framework-dev, Travis Geiselbrecht, Carlos Pizano, Nick Maniscalco

Yeah, https://fuchsia-review.googlesource.com/c/fuchsia/+/593646 is the work-in-progress. I'm trying to figure out how to test it at the moment.

Adam

Adam Barth

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Oct 13, 2021, 7:22:37 PM10/13/21

to Bryan Henry, component-framework-dev, Travis Geiselbrecht, Carlos Pizano, Nick Maniscalco

Figured out the test. CL is ready for review.

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