hermit-detcore 0.4.0

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree.
 */

//! cpuid interception

use raw_cpuid::CpuIdResult;

#[derive(Debug, Clone, Copy)]
pub struct InterceptedCpuid();

impl InterceptedCpuid {
    pub fn new() -> Self {
        InterceptedCpuid()
    }
}

impl InterceptedCpuid {
    pub fn cpuid(&self, leaf: u32, subleaf: u32) -> Option<CpuIdResult> {
        let request = leaf as usize;
        let result = if request >= 0x80000000 && request < 0x80000000 + EXTENDED_CPUIDS.len() {
            EXTENDED_CPUIDS[request - 0x80000000]
        } else if request < CPUIDS.len() {
            CPUIDS[request]
        } else {
            return None;
        };

        if subleaf != 0 && uses_subleaf(leaf) {
            Some(cpuid_result(0, 0, 0, 0))
        } else {
            Some(result)
        }
    }
}

/// Whether ECX selects an entry for a basic leaf represented by [`CPUIDS`].
fn uses_subleaf(leaf: u32) -> bool {
    matches!(leaf, 0x04 | 0x07 | 0x0b | 0x0d | 0x0f | 0x10 | 0x12 | 0x14)
}

const fn cpuid_result(eax: u32, ebx: u32, ecx: u32, edx: u32) -> CpuIdResult {
    CpuIdResult { eax, ebx, ecx, edx }
}

// CPUID output from older CPU (broadwell?), with some features like RDRAND
// masked off to prevent non-determinism.
const CPUIDS: &[CpuIdResult] = &[
    cpuid_result(0x0000000D, 0x756E6547, 0x6C65746E, 0x49656E69),
    cpuid_result(
        0x00000663,
        0x00000800,
        // These flags are required for x86-64-v2 support. Found via https://www.felixcloutier.com/x86/cpuid
        0x90202001 | (1 << 0) | (1 << 9) | (1 << 13) | (1 << 19) | (1 << 20) | (1 << 23),
        0x078BFBFD,
    ),
    cpuid_result(0x00000001, 0x00000000, 0x0000004D, 0x002C307D),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000120, 0x01C0003F, 0x0000003F, 0x00000001),
    cpuid_result(0x00000000, 0x00000000, 0x00000003, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00180FB9, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000001, 0x00000100, 0x00000001),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
];

const EXTENDED_CPUIDS: &[CpuIdResult] = &[
    cpuid_result(0x8000000A, 0x756E6547, 0x6C65746E, 0x49656E69),
    cpuid_result(0x00000663, 0x00000000, 0x00000001, 0x20100800),
    cpuid_result(0x554D4551, 0x72695620, 0x6C617574, 0x55504320),
    cpuid_result(0x72657620, 0x6E6F6973, 0x352E3220, 0x0000002B),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x01FF01FF, 0x01FF01FF, 0x40020140, 0x40020140),
    cpuid_result(0x00000000, 0x42004200, 0x02008140, 0x00808140),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00003028, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
    cpuid_result(0x00000000, 0x00000000, 0x00000000, 0x00000000),
];

#[cfg(test)]
mod tests {
    use super::*;

    fn registers(result: CpuIdResult) -> [u32; 4] {
        [result.eax, result.ebx, result.ecx, result.edx]
    }

    #[test]
    fn cpuid_leaf_count() {
        assert!(CPUIDS[0].eax as usize <= CPUIDS.len());
        assert_eq!(
            1 + (EXTENDED_CPUIDS[0].eax as usize & !0x80000000usize),
            EXTENDED_CPUIDS.len()
        );
    }

    #[test]
    fn indexed_leaves_do_not_alias_subleaf_zero() {
        let cpuid = InterceptedCpuid::new();

        assert_eq!(registers(cpuid.cpuid(0x07, 1).unwrap()), [0; 4]);
        for leaf in [0x04, 0x0b, 0x0d, 0x0f, 0x10, 0x12, 0x14] {
            assert_eq!(
                registers(cpuid.cpuid(leaf, 1).unwrap()),
                [0; 4],
                "leaf {leaf:#x}"
            );
        }
        assert_eq!(
            registers(cpuid.cpuid(0x07, 0).unwrap()),
            [0, 0x0018_0fb9, 0, 0]
        );
        assert_eq!(registers(cpuid.cpuid(0x0b, 0).unwrap()), [0, 1, 0x100, 1]);
    }

    #[test]
    fn nonindexed_leaves_ignore_subleaf() {
        let cpuid = InterceptedCpuid::new();

        for leaf in (0..CPUIDS.len() as u32).filter(|leaf| !uses_subleaf(*leaf)) {
            assert_eq!(
                registers(cpuid.cpuid(leaf, 0).unwrap()),
                registers(cpuid.cpuid(leaf, u32::MAX).unwrap()),
                "basic leaf {leaf:#x}"
            );
        }
        for offset in 0..EXTENDED_CPUIDS.len() as u32 {
            let leaf = 0x8000_0000 + offset;
            assert_eq!(
                registers(cpuid.cpuid(leaf, 0).unwrap()),
                registers(cpuid.cpuid(leaf, u32::MAX).unwrap()),
                "extended leaf {leaf:#x}"
            );
        }
    }
}