Reported

December 5, 2024

Issued

December 22, 2024

Package

kvm-ioctls (crates.io)

Type

INFO Unsound

Keywords

#unsound #1-82

References

• https://github.com/rust-vmm/kvm/pull/298

Patched

• >=0.19.1

Affected OSes

• linux

Affected Functions

Version

kvm_ioctls::ioctls::vm::VmFd::create_device

• <=0.19.0

Description

An issue was identified in the VmFd::create_device function, leading to undefined behavior and miscompilations on rustc 1.82.0 and newer due to the function's violation of Rust's pointer safety rules.

The function downcasted a mutable reference to its struct kvm_create_device argument to an immutable pointer, and then proceeded to pass this pointer to a mutating system call. Rustc 1.82.0 and newer elides subsequent reads of this structure's fields, meaning code will not see the value written by the kernel into the fd member. Instead, the code will observe the value that this field was initialized to prior to calling VmFd::create_device (usually, 0).

The issue started in kvm-ioctls 0.1.0 and was fixed in 0.19.1 by correctly using a mutable pointer.

Advisory available under CC0-1.0 license.