pvmfw/src/memory.rs

// Copyright 2022, The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Low-level allocation and tracking of main memory.

#![deny(unsafe_op_in_unsafe_fn)]

use crate::helpers::{self, align_down, align_up, page_4kb_of, SIZE_4KB};
use crate::mmu;
use alloc::alloc::alloc_zeroed;
use alloc::alloc::dealloc;
use alloc::alloc::handle_alloc_error;
use core::alloc::Layout;
use core::cmp::max;
use core::cmp::min;
use core::fmt;
use core::num::NonZeroUsize;
use core::ops::Range;
use core::ptr::NonNull;
use core::result;
use hyp::get_hypervisor;
use log::error;
use tinyvec::ArrayVec;

/// Base of the system's contiguous "main" memory.
pub const BASE_ADDR: usize = 0x8000_0000;
/// First address that can't be translated by a level 1 TTBR0_EL1.
pub const MAX_ADDR: usize = 1 << 40;

pub type MemoryRange = Range<usize>;

#[derive(Clone, Copy, Debug, Default)]
enum MemoryType {
    #[default]
    ReadOnly,
    ReadWrite,
}

#[derive(Clone, Debug, Default)]
struct MemoryRegion {
    range: MemoryRange,
    mem_type: MemoryType,
}

impl MemoryRegion {
    /// True if the instance overlaps with the passed range.
    pub fn overlaps(&self, range: &MemoryRange) -> bool {
        overlaps(&self.range, range)
    }

    /// True if the instance is fully contained within the passed range.
    pub fn is_within(&self, range: &MemoryRange) -> bool {
        let our: &MemoryRange = self.as_ref();
        self.as_ref() == &(max(our.start, range.start)..min(our.end, range.end))
    }
}

impl AsRef<MemoryRange> for MemoryRegion {
    fn as_ref(&self) -> &MemoryRange {
        &self.range
    }
}

/// Returns true if one range overlaps with the other at all.
fn overlaps<T: Copy + Ord>(a: &Range<T>, b: &Range<T>) -> bool {
    max(a.start, b.start) < min(a.end, b.end)
}

/// Tracks non-overlapping slices of main memory.
pub struct MemoryTracker {
    total: MemoryRange,
    page_table: mmu::PageTable,
    regions: ArrayVec<[MemoryRegion; MemoryTracker::CAPACITY]>,
    mmio_regions: ArrayVec<[MemoryRange; MemoryTracker::MMIO_CAPACITY]>,
}

/// Errors for MemoryTracker operations.
#[derive(Debug, Clone)]
pub enum MemoryTrackerError {
    /// Tried to modify the memory base address.
    DifferentBaseAddress,
    /// Tried to shrink to a larger memory size.
    SizeTooLarge,
    /// Tracked regions would not fit in memory size.
    SizeTooSmall,
    /// Reached limit number of tracked regions.
    Full,
    /// Region is out of the tracked memory address space.
    OutOfRange,
    /// New region overlaps with tracked regions.
    Overlaps,
    /// Region couldn't be mapped.
    FailedToMap,
    /// Error from the interaction with the hypervisor.
    Hypervisor(hyp::Error),
}

impl fmt::Display for MemoryTrackerError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Self::DifferentBaseAddress => write!(f, "Received different base address"),
            Self::SizeTooLarge => write!(f, "Tried to shrink to a larger memory size"),
            Self::SizeTooSmall => write!(f, "Tracked regions would not fit in memory size"),
            Self::Full => write!(f, "Reached limit number of tracked regions"),
            Self::OutOfRange => write!(f, "Region is out of the tracked memory address space"),
            Self::Overlaps => write!(f, "New region overlaps with tracked regions"),
            Self::FailedToMap => write!(f, "Failed to map the new region"),
            Self::Hypervisor(e) => e.fmt(f),
        }
    }
}

impl From<hyp::Error> for MemoryTrackerError {
    fn from(e: hyp::Error) -> Self {
        Self::Hypervisor(e)
    }
}

type Result<T> = result::Result<T, MemoryTrackerError>;

impl MemoryTracker {
    const CAPACITY: usize = 5;
    const MMIO_CAPACITY: usize = 5;

    /// Create a new instance from an active page table, covering the maximum RAM size.
    pub fn new(page_table: mmu::PageTable) -> Self {
        Self {
            total: BASE_ADDR..MAX_ADDR,
            page_table,
            regions: ArrayVec::new(),
            mmio_regions: ArrayVec::new(),
        }
    }

    /// Resize the total RAM size.
    ///
    /// This function fails if it contains regions that are not included within the new size.
    pub fn shrink(&mut self, range: &MemoryRange) -> Result<()> {
        if range.start != self.total.start {
            return Err(MemoryTrackerError::DifferentBaseAddress);
        }
        if self.total.end < range.end {
            return Err(MemoryTrackerError::SizeTooLarge);
        }
        if !self.regions.iter().all(|r| r.is_within(range)) {
            return Err(MemoryTrackerError::SizeTooSmall);
        }

        self.total = range.clone();
        Ok(())
    }

    /// Allocate the address range for a const slice; returns None if failed.
    pub fn alloc_range(&mut self, range: &MemoryRange) -> Result<MemoryRange> {
        let region = MemoryRegion { range: range.clone(), mem_type: MemoryType::ReadOnly };
        self.check(&region)?;
        self.page_table.map_rodata(range).map_err(|e| {
            error!("Error during range allocation: {e}");
            MemoryTrackerError::FailedToMap
        })?;
        self.add(region)
    }

    /// Allocate the address range for a mutable slice; returns None if failed.
    pub fn alloc_range_mut(&mut self, range: &MemoryRange) -> Result<MemoryRange> {
        let region = MemoryRegion { range: range.clone(), mem_type: MemoryType::ReadWrite };
        self.check(&region)?;
        self.page_table.map_data(range).map_err(|e| {
            error!("Error during mutable range allocation: {e}");
            MemoryTrackerError::FailedToMap
        })?;
        self.add(region)
    }

    /// Allocate the address range for a const slice; returns None if failed.
    pub fn alloc(&mut self, base: usize, size: NonZeroUsize) -> Result<MemoryRange> {
        self.alloc_range(&(base..(base + size.get())))
    }

    /// Allocate the address range for a mutable slice; returns None if failed.
    pub fn alloc_mut(&mut self, base: usize, size: NonZeroUsize) -> Result<MemoryRange> {
        self.alloc_range_mut(&(base..(base + size.get())))
    }

    /// Checks that the given range of addresses is within the MMIO region, and then maps it
    /// appropriately.
    pub fn map_mmio_range(&mut self, range: MemoryRange) -> Result<()> {
        // MMIO space is below the main memory region.
        if range.end > self.total.start {
            return Err(MemoryTrackerError::OutOfRange);
        }
        if self.mmio_regions.iter().any(|r| overlaps(r, &range)) {
            return Err(MemoryTrackerError::Overlaps);
        }
        if self.mmio_regions.len() == self.mmio_regions.capacity() {
            return Err(MemoryTrackerError::Full);
        }

        self.page_table.map_device(&range).map_err(|e| {
            error!("Error during MMIO device mapping: {e}");
            MemoryTrackerError::FailedToMap
        })?;

        for page_base in page_iterator(&range) {
            get_hypervisor().mmio_guard_map(page_base)?;
        }

        if self.mmio_regions.try_push(range).is_some() {
            return Err(MemoryTrackerError::Full);
        }

        Ok(())
    }

    /// Checks that the given region is within the range of the `MemoryTracker` and doesn't overlap
    /// with any other previously allocated regions, and that the regions ArrayVec has capacity to
    /// add it.
    fn check(&self, region: &MemoryRegion) -> Result<()> {
        if !region.is_within(&self.total) {
            return Err(MemoryTrackerError::OutOfRange);
        }
        if self.regions.iter().any(|r| r.overlaps(&region.range)) {
            return Err(MemoryTrackerError::Overlaps);
        }
        if self.regions.len() == self.regions.capacity() {
            return Err(MemoryTrackerError::Full);
        }
        Ok(())
    }

    fn add(&mut self, region: MemoryRegion) -> Result<MemoryRange> {
        if self.regions.try_push(region).is_some() {
            return Err(MemoryTrackerError::Full);
        }

        Ok(self.regions.last().unwrap().as_ref().clone())
    }

    /// Unmaps all tracked MMIO regions from the MMIO guard.
    ///
    /// Note that they are not unmapped from the page table.
    pub fn mmio_unmap_all(&self) -> Result<()> {
        for region in &self.mmio_regions {
            for page_base in page_iterator(region) {
                get_hypervisor().mmio_guard_unmap(page_base)?;
            }
        }

        Ok(())
    }
}

impl Drop for MemoryTracker {
    fn drop(&mut self) {
        for region in &self.regions {
            match region.mem_type {
                MemoryType::ReadWrite => {
                    // TODO(b/269738062): Use PT's dirty bit to only flush pages that were touched.
                    helpers::flush_region(region.range.start, region.range.len())
                }
                MemoryType::ReadOnly => {}
            }
        }
    }
}

/// Gives the KVM host read, write and execute permissions on the given memory range. If the range
/// is not aligned with the memory protection granule then it will be extended on either end to
/// align.
fn share_range(range: &MemoryRange, granule: usize) -> hyp::Result<()> {
    for base in (align_down(range.start, granule)
        .expect("Memory protection granule was not a power of two")..range.end)
        .step_by(granule)
    {
        get_hypervisor().mem_share(base as u64)?;
    }
    Ok(())
}

/// Removes permission from the KVM host to access the given memory range which was previously
/// shared. If the range is not aligned with the memory protection granule then it will be extended
/// on either end to align.
fn unshare_range(range: &MemoryRange, granule: usize) -> hyp::Result<()> {
    for base in (align_down(range.start, granule)
        .expect("Memory protection granule was not a power of two")..range.end)
        .step_by(granule)
    {
        get_hypervisor().mem_unshare(base as u64)?;
    }
    Ok(())
}

/// Allocates a memory range of at least the given size from the global allocator, and shares it
/// with the host. Returns a pointer to the buffer.
///
/// It will be aligned to the memory sharing granule size supported by the hypervisor.
pub fn alloc_shared(size: usize) -> hyp::Result<NonNull<u8>> {
    let layout = shared_buffer_layout(size)?;
    let granule = layout.align();

    // Safe because `shared_buffer_layout` panics if the size is 0, so the layout must have a
    // non-zero size.
    let buffer = unsafe { alloc_zeroed(layout) };

    let Some(buffer) = NonNull::new(buffer) else {
        handle_alloc_error(layout);
    };

    let paddr = virt_to_phys(buffer);
    // If share_range fails then we will leak the allocation, but that seems better than having it
    // be reused while maybe still partially shared with the host.
    share_range(&(paddr..paddr + layout.size()), granule)?;

    Ok(buffer)
}

/// Unshares and deallocates a memory range which was previously allocated by `alloc_shared`.
///
/// The size passed in must be the size passed to the original `alloc_shared` call.
///
/// # Safety
///
/// The memory must have been allocated by `alloc_shared` with the same size, and not yet
/// deallocated.
pub unsafe fn dealloc_shared(vaddr: NonNull<u8>, size: usize) -> hyp::Result<()> {
    let layout = shared_buffer_layout(size)?;
    let granule = layout.align();

    let paddr = virt_to_phys(vaddr);
    unshare_range(&(paddr..paddr + layout.size()), granule)?;
    // Safe because the memory was allocated by `alloc_shared` above using the same allocator, and
    // the layout is the same as was used then.
    unsafe { dealloc(vaddr.as_ptr(), layout) };

    Ok(())
}

/// Returns the layout to use for allocating a buffer of at least the given size shared with the
/// host.
///
/// It will be aligned to the memory sharing granule size supported by the hypervisor.
///
/// Panics if `size` is 0.
fn shared_buffer_layout(size: usize) -> hyp::Result<Layout> {
    assert_ne!(size, 0);
    let granule = get_hypervisor().memory_protection_granule()?;
    let allocated_size =
        align_up(size, granule).expect("Memory protection granule was not a power of two");
    Ok(Layout::from_size_align(allocated_size, granule).unwrap())
}

/// Returns an iterator which yields the base address of each 4 KiB page within the given range.
fn page_iterator(range: &MemoryRange) -> impl Iterator<Item = usize> {
    (page_4kb_of(range.start)..range.end).step_by(SIZE_4KB)
}

/// Returns the intermediate physical address corresponding to the given virtual address.
///
/// As we use identity mapping for everything, this is just a cast, but it's useful to use it to be
/// explicit about where we are converting from virtual to physical address.
pub fn virt_to_phys(vaddr: NonNull<u8>) -> usize {
    vaddr.as_ptr() as _
}

/// Returns a pointer for the virtual address corresponding to the given non-zero intermediate
/// physical address.
///
/// Panics if `paddr` is 0.
pub fn phys_to_virt(paddr: usize) -> NonNull<u8> {
    NonNull::new(paddr as _).unwrap()
}