Manually load ELF binaries

[jstarks]

Parse and load ELF binaries manually instead of using the elf_loader crate. This is done for a few reasons:

• elf_loader is not safe for our use--it assumes it can safely access mapped memory directly via Rust memory access primitives--this is not always true for LiteBox since that memory is user-mode memory. Even when we know there are no other guest threads, so that concurrent mutation should be impossible, we still need to handle that memory differently from Rust memory.

• elf_loader creates a dependency on shim TLS to get the task object, since the various mmap-related traits do not take &self. This prevents some future refactoring to eliminate the use of TLS within the shims. Fixing this upstream seems like a big change, one that would break semver compatibility.

• elf_loader seems to combine parsing and mapping operations into one step, preventing us from returning errors from execve when the target binary is not a valid ELF executable.

• elf_loader has an awful lot of code marked unsafe with safety contracts that are unclear (to me).

• Loading the binary is a pretty important part of the Linux and OPTEE shims--we want to have a good understanding and control over exactly what loader ABI we are actually implementing.

For now, just update the Linux shim to use this new loader--this work has uncovered some design problems with OPTEE that need to be addressed before we can remove the dependency on elf_loader.

[wdcui]

Thank you for adding our own elf loader, John! The code looks good to me. I left some minor comments. Please wait for the reviews of @sangho2 and @CvvT before you merge this PR.

[sangho2]

It seems that this new ELF loader has a problem with the KMPP TA (other three TAs work well). I'll take a look at it more.

cargo run -p litebox_runner_optee_on_linux_userland litebox_runner_optee_on_linux_userland/tests/kmpp-ta.elf.hooked litebox_runner_optee_on_linux_userland/tests/kmpp-ta-cmds.json

[jstarks]

It seems that this new ELF loader has a problem with the KMPP TA (other three TAs work well). I'll take a look at it more.

cargo run -p litebox_runner_optee_on_linux_userland litebox_runner_optee_on_linux_userland/tests/kmpp-ta.elf.hooked litebox_runner_optee_on_linux_userland/tests/kmpp-ta-cmds.json

Is KMPP TA not part of the CI tests?

[jstarks]

Hmm, I see, KMPP-TA fails to run but the test succeeds anyway...

[wdcui]

@sangho2 @CvvT, if you think this PR is ready to be merged, please approve it. Thanks!

[CvvT]

LGTM! Thanks! I left one comment. Feel free to merge once all conflicts are resolved.

[github-actions]

🤖 SemverChecks 🤖 ⚠️ Potential breaking API changes detected ⚠️

Click for details

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.45.0/src/lints/enum_missing.ron

Failed in:
  enum litebox_shim_linux::loader::ElfLoaderError, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/ba97c2833b325e6735f9be1f2938a269c93edf95/litebox_shim_linux/src/loader/elf.rs:470

--- failure pub_module_level_const_missing: pub module-level const is missing ---

Description:
A public const is missing or renamed
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.45.0/src/lints/pub_module_level_const_missing.ron

Failed in:
  REWRITER_VERSION_NUMBER in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/ba97c2833b325e6735f9be1f2938a269c93edf95/litebox_shim_linux/src/loader/mod.rs:25
  REWRITER_MAGIC_NUMBER in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/ba97c2833b325e6735f9be1f2938a269c93edf95/litebox_shim_linux/src/loader/mod.rs:24

--- failure struct_missing: pub struct removed or renamed ---

Description:
A publicly-visible struct cannot be imported by its prior path. A `pub use` may have been removed, or the struct itself may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.45.0/src/lints/struct_missing.ron

Failed in:
  struct litebox_shim_linux::loader::ElfLoadInfo, previously in file /home/runner/work/litebox/litebox/target/semver-checks/git-main/ba97c2833b325e6735f9be1f2938a269c93edf95/litebox_shim_linux/src/loader/elf.rs:210

[CvvT]

The test test_tun_tcp_socket_as_client seems to be flaky; I will take a look.