ASLR support

[n0toose]

• Move x86_64-related paging code to src/arch/x86_64/paging
• Tests: x86_64-related paging tests should use a guest_address that is
  not 0
• Tests: Move them in separate files, use appropriate 'use' directives
• Tests: Use init_guest_mem wrapper in test_virt_to_phys
• Fix kernel memory loading
• Add guest_address getter in UhyveVm
• Change names of constants to clarify their purpose
• Remove pagetable_l0 from virt_to_phys function
• Various cargo fmt-related changes
• aarch64: Blindly replace constant names and similar RAM_START change

We currently rely on guest_address in MmapMemory to calculate the
offsets during the initialization of the VM and when converting
virtual addresses to physical addresses. The latter case is intended
to be temporary - we should read the value from the CR3 register at
a later point.

Although this current revision does work with relocatable binaries, it
is not making use of this functionality just yet.

Fixes #719.
Fixes #713.

[n0toose]

This change was not tested on macOS (x86_64, aarch64) because of a lack of hardware, and, in the case of macOS (x86_64), there's no CI - I may have to bring up a VM for this, but it will take at least an hour to prepare it. This involved some guess work in both aarch64 and x86_64 - because of this, I will explicitly disable the upcoming ASLR feature in both of these cases.

The change looks artificially bigger than it is because of the x86_64 paging code being moved to a separate file. This is easy for me to undo.

• This is a rebased and somewhat "cleaned up" version of https://github.com/n0toose/uhyve/tree/make-it-boot (might help with the review), plus lots of tiny changes:
  • I had to fix lots of things in aarch64 (very often, formatting mistakes caught by cargo fmt).
  • Everything aarch64 and macOS-related is not part of the tree
• Despite the refactoring, the guest_address should always be zero for the time being. The work to change this was done here: ASLR: PoC for generating random address before Uhyve launches #711
• These two changes were kept separate because of the very big scope of this change - and because some further thought has to be poured into the case of the hello_c case.

[codecov]

Codecov Report

Attention: Patch coverage is 90.55375% with 29 lines in your changes missing coverage. Please review.

Project coverage is 71.11%. Comparing base (ce8173c) to head (e4a1090).

Files with missing lines	Patch %	Lines
src/vm.rs	82.71%	14 Missing ⚠️
src/arch/x86_64/paging/mod.rs	90.83%	12 Missing ⚠️
src/bin/uhyve.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #725      +/-   ##
==========================================
+ Coverage   70.26%   71.11%   +0.85%     
==========================================
  Files          24       25       +1     
  Lines        2959     3123     +164     
==========================================
+ Hits         2079     2221     +142     
- Misses        880      902      +22     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[n0toose]

I spent 15 minutes trying to give more context behind the macOS changes on x86_64 and aarch64 to help the review process - where I tried to change the least amount of things possible until the compiler stopped being mad at me (and as a way of double-checking the changes).

The goal is to have this changed merged directly into main or in a feature branch, so that I can continue working on top of these foundations. Hope this helps.

(EDIT: I marked all of these comments as "resolved" to keep the PR log cleaner.)

[n0toose]

Some notes on the latest revision which does not fully work...

[jounathaen]

Currently blocked as we need a release with hermit-os/kernel#1508

[jounathaen]

Remaining tasks:

• add a CLI option to disable ASLR
• Implement ASLR on aarch64
• remove duplicate kernel parsing
• Add mapping of the first GiB to support legacy kernels, or add a version check to only support recent kernels and rebuild hello_world and rusty_demo