So, in case you’ve ever wondered, this is how you map anonymous memory with vm-memory crate:
//! Copyright (c) Jarkko Sakkinen 2024
#![deny(clippy::all)]
#![deny(clippy::pedantic)]
use vm_memory::{GuestAddress, GuestMemoryMmap};
fn main() {
let mem: GuestMemoryMmap<()> =
GuestMemoryMmap::from_ranges(&[(GuestAddress(0u64), 8192usize)]).unwrap();
println!("{:?}", mem);
}
The type parameter is for Bitmap.
I’ll do a small test program for each type of memory that we need in Enarx and after that make the changes to the project itself. Changes are simple but the code base is large so this is fastest way to formalize a decent patch.
So next step is /dev/kvm
test.
Output:
~/work/local/hello-vm-memory master* 7m 13s
❯ target/debug/hello-vm-memory
GuestMemoryMmap { regions: [GuestRegionMmap { mapping: MmapRegion { addr: 0x7f593adbf000, size: 8192, bitmap: (), file_offset: None, prot: 3, flags: 16418, owned: true, hugetlbfs: None }, guest_base: GuestAddress(0) }] }
Turns out that vm-memory is WRONG crate for arbitrary mappings. E.g. it does not allows arbitray permissions for anonymous mappings. Instead mmap-rs is probably better idea:
// SPDX-License-Identifier: MIT
//! Copyright (c) Jarkko Sakkinen 2024
#![deny(clippy::all)]
#![deny(clippy::pedantic)]
use mmap::MemoryMap;
fn main() {
let mem = MemoryMap::new(0x2000, &[
mmap::MapOption::MapReadable,
mmap::MapOption::MapWritable,
mmap::MapOption::MapExecutable,
]).unwrap_or_else(|_| std::process::exit(1));
println!("{}", mem.len());
}
MapOption
contains fields for file and similar stuff too.
@jarkko note that memmap is [unmaintained](https://rustsec.org/advisories/RUSTSEC-2020-0077.html) you almost certainly want memmap2
@Dr_Emann Not fully yet understanding capabilities of vm-memory but enarx has two kinds of mappings:
So I’m looking into if I could extend vm-memory to provide the latter so then host/guest mmaps would have same parameters and two internal crates could be removed.
So lot’s of experimentation to do before it make sense to do anything for the actual project. If this draft of an idea would be possible with vm-memory, it would make doing the task whole a lot more feasible.