capsules_extra/

hmac.rs

// Licensed under the Apache License, Version 2.0 or the MIT License.
// SPDX-License-Identifier: Apache-2.0 OR MIT
// Copyright Tock Contributors 2022.

//! HMAC (Hash-based Message Authentication Code).
//!
//! Usage
//! -----
//!
//! ```rust,ignore
//! let hmac = &earlgrey::hmac::HMAC;
//!
//! let mux_hmac = static_init!(MuxHmac<'static, lowrisc::hmac::Hmac>, MuxHmac::new(hmac));
//! digest::Digest::set_client(&earlgrey::hmac::HMAC, mux_hmac);
//!
//! let virtual_hmac_user = static_init!(
//!     VirtualMuxHmac<'static, lowrisc::hmac::Hmac>,
//!     VirtualMuxHmac::new(mux_hmac)
//! );
//! let hmac = static_init!(
//!     capsules::hmac::HmacDriver<'static, VirtualMuxHmac<'static, lowrisc::hmac::Hmac>>,
//!     capsules::hmac::HmacDriver::new(
//!         virtual_hmac_user,
//!         board_kernel.create_grant(&memory_allocation_cap),
//!     )
//! );
//! digest::Digest::set_client(virtual_hmac_user, hmac);
//! ```

use capsules_core::driver;
use kernel::errorcode::into_statuscode;
/// Syscall driver number.
pub const DRIVER_NUM: usize = driver::NUM::Hmac as usize;

/// Ids for read-only allow buffers
mod ro_allow {
    pub const KEY: usize = 0;
    pub const DATA: usize = 1;
    pub const COMPARE: usize = 2;
    /// The number of allow buffers the kernel stores for this grant
    pub const COUNT: u8 = 3;
}

/// Ids for read-write allow buffers
mod rw_allow {
    pub const DEST: usize = 2;
    /// The number of allow buffers the kernel stores for this grant
    pub const COUNT: u8 = 3;
}

use core::cell::Cell;

use kernel::grant::{AllowRoCount, AllowRwCount, Grant, UpcallCount};
use kernel::hil::digest;
use kernel::processbuffer::{ReadableProcessBuffer, WriteableProcessBuffer};
use kernel::syscall::{CommandReturn, SyscallDriver};
use kernel::utilities::cells::{OptionalCell, TakeCell};
use kernel::utilities::leasable_buffer::SubSlice;
use kernel::utilities::leasable_buffer::SubSliceMut;
use kernel::{ErrorCode, ProcessId};

enum ShaOperation {
    Sha256,
    Sha384,
    Sha512,
}

// Temporary buffer to copy the keys from userspace into
//
// Needs to be able to accommodate the largest key sizes, e.g. 512
const TMP_KEY_BUFFER_SIZE: usize = 512 / 8;

pub struct HmacDriver<'a, H: digest::Digest<'a, L>, const L: usize> {
    hmac: &'a H,

    active: Cell<bool>,

    apps: Grant<
        App,
        UpcallCount<1>,
        AllowRoCount<{ ro_allow::COUNT }>,
        AllowRwCount<{ rw_allow::COUNT }>,
    >,
    processid: OptionalCell<ProcessId>,

    data_buffer: TakeCell<'static, [u8]>,
    data_copied: Cell<usize>,
    dest_buffer: TakeCell<'static, [u8; L]>,
}

impl<
        'a,
        H: digest::Digest<'a, L> + digest::HmacSha256 + digest::HmacSha384 + digest::HmacSha512,
        const L: usize,
    > HmacDriver<'a, H, L>
{
    pub fn new(
        hmac: &'a H,
        data_buffer: &'static mut [u8],
        dest_buffer: &'static mut [u8; L],
        grant: Grant<
            App,
            UpcallCount<1>,
            AllowRoCount<{ ro_allow::COUNT }>,
            AllowRwCount<{ rw_allow::COUNT }>,
        >,
    ) -> HmacDriver<'a, H, L> {
        HmacDriver {
            hmac,
            active: Cell::new(false),
            apps: grant,
            processid: OptionalCell::empty(),
            data_buffer: TakeCell::new(data_buffer),
            data_copied: Cell::new(0),
            dest_buffer: TakeCell::new(dest_buffer),
        }
    }

    fn run(&self) -> Result<(), ErrorCode> {
        self.processid.map_or(Err(ErrorCode::RESERVE), |processid| {
            self.apps
                .enter(processid, |app, kernel_data| {
                    kernel_data
                        .get_readonly_processbuffer(ro_allow::KEY)
                        .and_then(|key| {
                            key.enter(|k| {
                                if let Some(op) = &app.sha_operation {
                                    let mut tmp_key_buffer: [u8; TMP_KEY_BUFFER_SIZE] =
                                        [0; TMP_KEY_BUFFER_SIZE];
                                    let key_len = core::cmp::min(k.len(), TMP_KEY_BUFFER_SIZE);
                                    k[..key_len].copy_to_slice(&mut tmp_key_buffer[..key_len]);

                                    match op {
                                        ShaOperation::Sha256 => self
                                            .hmac
                                            .set_mode_hmacsha256(&tmp_key_buffer[..key_len]),
                                        ShaOperation::Sha384 => self
                                            .hmac
                                            .set_mode_hmacsha384(&tmp_key_buffer[..key_len]),
                                        ShaOperation::Sha512 => self
                                            .hmac
                                            .set_mode_hmacsha512(&tmp_key_buffer[..key_len]),
                                    }
                                } else {
                                    Err(ErrorCode::INVAL)
                                }
                            })
                        })
                        .unwrap_or(Err(ErrorCode::RESERVE))?;

                    kernel_data
                        .get_readonly_processbuffer(ro_allow::DATA)
                        .and_then(|data| {
                            data.enter(|data| {
                                let mut static_buffer_len = 0;
                                self.data_buffer.map(|buf| {
                                    // Determine the size of the static buffer we have
                                    static_buffer_len = buf.len();

                                    if static_buffer_len > data.len() {
                                        static_buffer_len = data.len()
                                    }

                                    self.data_copied.set(static_buffer_len);

                                    // Copy the data into the static buffer
                                    data[..static_buffer_len]
                                        .copy_to_slice(&mut buf[..static_buffer_len]);
                                });

                                // Add the data from the static buffer to the HMAC
                                let mut lease_buf = SubSliceMut::new(
                                    self.data_buffer.take().ok_or(ErrorCode::RESERVE)?,
                                );
                                lease_buf.slice(0..static_buffer_len);
                                if let Err(e) = self.hmac.add_mut_data(lease_buf) {
                                    self.data_buffer.replace(e.1.take());
                                    return Err(e.0);
                                }
                                Ok(())
                            })
                        })
                        .unwrap_or(Err(ErrorCode::RESERVE))
                })
                .unwrap_or_else(|err| Err(err.into()))
        })
    }

    fn calculate_digest(&self) -> Result<(), ErrorCode> {
        self.data_copied.set(0);

        if let Err(e) = self
            .hmac
            .run(self.dest_buffer.take().ok_or(ErrorCode::RESERVE)?)
        {
            // Error, clear the processid and data
            self.hmac.clear_data();
            self.processid.clear();
            self.dest_buffer.replace(e.1);

            return Err(e.0);
        }

        Ok(())
    }

    fn verify_digest(&self) -> Result<(), ErrorCode> {
        self.data_copied.set(0);

        if let Err(e) = self
            .hmac
            .verify(self.dest_buffer.take().ok_or(ErrorCode::RESERVE)?)
        {
            // Error, clear the processid and data
            self.hmac.clear_data();
            self.processid.clear();
            self.dest_buffer.replace(e.1);

            return Err(e.0);
        }

        Ok(())
    }

    fn check_queue(&self) {
        for appiter in self.apps.iter() {
            let started_command = appiter.enter(|app, _| {
                // If an app is already running let it complete
                if self.processid.is_some() {
                    return true;
                }

                // If this app has a pending command let's use it.
                app.pending_run_app.take().is_some_and(|processid| {
                    // Mark this driver as being in use.
                    self.processid.set(processid);
                    // Actually make the buzz happen.
                    self.run() == Ok(())
                })
            });
            if started_command {
                break;
            }
        }
    }
}

impl<
        'a,
        H: digest::Digest<'a, L> + digest::HmacSha256 + digest::HmacSha384 + digest::HmacSha512,
        const L: usize,
    > digest::ClientData<L> for HmacDriver<'a, H, L>
{
    // Because data needs to be copied from a userspace buffer into a kernel (RAM) one,
    // we always pass mut data; this callback should never be invoked.
    fn add_data_done(&self, _result: Result<(), ErrorCode>, _data: SubSlice<'static, u8>) {}

    fn add_mut_data_done(&self, _result: Result<(), ErrorCode>, data: SubSliceMut<'static, u8>) {
        self.processid.map(move |id| {
            self.apps
                .enter(id, move |app, kernel_data| {
                    let mut data_len = 0;
                    let mut exit = false;
                    let mut static_buffer_len = 0;

                    self.data_buffer.replace(data.take());

                    self.data_buffer.map(|buf| {
                        let ret = kernel_data
                            .get_readonly_processbuffer(ro_allow::DATA)
                            .and_then(|data| {
                                data.enter(|data| {
                                    // Determine the size of the static buffer we have
                                    static_buffer_len = buf.len();
                                    // Determine how much data we have already copied
                                    let copied_data = self.data_copied.get();

                                    data_len = data.len();

                                    if data_len > copied_data {
                                        let remaining_data = &data[copied_data..];
                                        let remaining_len = data_len - copied_data;

                                        if remaining_len < static_buffer_len {
                                            remaining_data.copy_to_slice(&mut buf[..remaining_len]);
                                        } else {
                                            remaining_data[..static_buffer_len].copy_to_slice(buf);
                                        }
                                    }
                                    Ok(())
                                })
                            })
                            .unwrap_or(Err(ErrorCode::RESERVE));

                        if ret == Err(ErrorCode::RESERVE) {
                            // No data buffer, clear the processid and data
                            self.hmac.clear_data();
                            self.processid.clear();
                            exit = true;
                        }
                    });

                    if exit {
                        return;
                    }

                    if static_buffer_len > 0 {
                        let copied_data = self.data_copied.get();

                        if data_len > copied_data {
                            // Update the amount of data copied
                            self.data_copied.set(copied_data + static_buffer_len);

                            let mut lease_buf = SubSliceMut::new(self.data_buffer.take().unwrap());

                            // Add the data from the static buffer to the HMAC
                            if data_len < (copied_data + static_buffer_len) {
                                lease_buf.slice(..(data_len - copied_data))
                            }

                            if self.hmac.add_mut_data(lease_buf).is_err() {
                                // Error, clear the processid and data
                                self.hmac.clear_data();
                                self.processid.clear();
                                return;
                            }

                            // Return as we don't want to run the digest yet
                            return;
                        }
                    }

                    // If we get here we are ready to run the digest, reset the copied data
                    if app.op.get().unwrap() == UserSpaceOp::Run {
                        if let Err(e) = self.calculate_digest() {
                            kernel_data
                                .schedule_upcall(0, (into_statuscode(e.into()), 0, 0))
                                .ok();
                        }
                    } else if app.op.get().unwrap() == UserSpaceOp::Verify {
                        let _ = kernel_data
                            .get_readonly_processbuffer(ro_allow::COMPARE)
                            .and_then(|compare| {
                                compare.enter(|compare| {
                                    let mut static_buffer_len = 0;
                                    self.dest_buffer.map(|buf| {
                                        // Determine the size of the static buffer we have
                                        static_buffer_len = buf.len();

                                        if static_buffer_len > compare.len() {
                                            static_buffer_len = compare.len()
                                        }

                                        self.data_copied.set(static_buffer_len);

                                        // Copy the data into the static buffer
                                        compare[..static_buffer_len]
                                            .copy_to_slice(&mut buf[..static_buffer_len]);
                                    });
                                })
                            });

                        if let Err(e) = self.verify_digest() {
                            kernel_data
                                .schedule_upcall(1, (into_statuscode(e.into()), 0, 0))
                                .ok();
                        }
                    } else {
                        kernel_data.schedule_upcall(0, (0, 0, 0)).ok();
                    }
                })
                .map_err(|err| {
                    if err == kernel::process::Error::NoSuchApp
                        || err == kernel::process::Error::InactiveApp
                    {
                        self.processid.clear();
                    }
                })
        });

        self.check_queue();
    }
}

impl<
        'a,
        H: digest::Digest<'a, L> + digest::HmacSha256 + digest::HmacSha384 + digest::HmacSha512,
        const L: usize,
    > digest::ClientHash<L> for HmacDriver<'a, H, L>
{
    fn hash_done(&self, result: Result<(), ErrorCode>, digest: &'static mut [u8; L]) {
        self.processid.map(|id| {
            self.apps
                .enter(id, |_, kernel_data| {
                    self.hmac.clear_data();

                    let pointer = digest[0] as *mut u8;

                    let _ = kernel_data
                        .get_readwrite_processbuffer(rw_allow::DEST)
                        .and_then(|dest| {
                            dest.mut_enter(|dest| {
                                let len = dest.len();

                                if len < L {
                                    dest.copy_from_slice(&digest[0..len]);
                                } else {
                                    dest[0..L].copy_from_slice(digest);
                                }
                            })
                        });

                    match result {
                        Ok(()) => kernel_data.schedule_upcall(0, (0, pointer as usize, 0)),
                        Err(e) => kernel_data
                            .schedule_upcall(0, (into_statuscode(e.into()), pointer as usize, 0)),
                    }
                    .ok();

                    // Clear the current processid as it has finished running
                    self.processid.clear();
                })
                .map_err(|err| {
                    if err == kernel::process::Error::NoSuchApp
                        || err == kernel::process::Error::InactiveApp
                    {
                        self.processid.clear();
                    }
                })
        });

        self.check_queue();
        self.dest_buffer.replace(digest);
    }
}

impl<
        'a,
        H: digest::Digest<'a, L> + digest::HmacSha256 + digest::HmacSha384 + digest::HmacSha512,
        const L: usize,
    > digest::ClientVerify<L> for HmacDriver<'a, H, L>
{
    fn verification_done(&self, result: Result<bool, ErrorCode>, compare: &'static mut [u8; L]) {
        self.processid.map(|id| {
            self.apps
                .enter(id, |_app, kernel_data| {
                    self.hmac.clear_data();

                    match result {
                        Ok(equal) => kernel_data.schedule_upcall(1, (0, equal as usize, 0)),
                        Err(e) => kernel_data.schedule_upcall(1, (into_statuscode(e.into()), 0, 0)),
                    }
                    .ok();

                    // Clear the current processid as it has finished running
                    self.processid.clear();
                })
                .map_err(|err| {
                    if err == kernel::process::Error::NoSuchApp
                        || err == kernel::process::Error::InactiveApp
                    {
                        self.processid.clear();
                    }
                })
        });

        self.check_queue();
        self.dest_buffer.replace(compare);
    }
}

/// Specify memory regions to be used.
///
/// ### `allow_num`
///
/// - `0`: Allow a buffer for storing the key. The kernel will read from this
///   when running This should not be changed after running `run` until the HMAC
///   has completed
/// - `1`: Allow a buffer for storing the buffer. The kernel will read from this
///   when running This should not be changed after running `run` until the HMAC
///   has completed
/// - `2`: Allow a buffer for storing the digest. The kernel will fill this with
///   the HMAC digest before calling the `hash_done` callback.
impl<
        'a,
        H: digest::Digest<'a, L> + digest::HmacSha256 + digest::HmacSha384 + digest::HmacSha512,
        const L: usize,
    > SyscallDriver for HmacDriver<'a, H, L>
{
    // Subscribe to HmacDriver events.
    //
    // ### `subscribe_num`
    //
    // - `0`: Subscribe to interrupts from HMAC events. The callback signature
    //   is `fn(result: u32)`

    /// Setup and run the HMAC hardware
    ///
    /// We expect userspace to setup buffers for the key, data and digest.
    /// These buffers must be allocated and specified to the kernel from the
    /// above allow calls.
    ///
    /// We expect userspace not to change the value while running. If userspace
    /// changes the value we have no guarantee of what is passed to the
    /// hardware. This isn't a security issue, it will just prove the requesting
    /// app with invalid data.
    ///
    /// The driver will take care of clearing data from the underlying implementation
    /// by calling the `clear_data()` function when the `hash_complete()` callback
    /// is called or if an error is encountered.
    ///
    /// ### `command_num`
    ///
    /// - `0`: set_algorithm
    /// - `1`: run
    /// - `2`: update
    /// - `3`: finish
    fn command(
        &self,
        command_num: usize,
        data1: usize,
        _data2: usize,
        processid: ProcessId,
    ) -> CommandReturn {
        let match_or_empty_or_nonexistant = self.processid.map_or(true, |owning_app| {
            // We have recorded that an app has ownership of the HMAC.

            // If the HMAC is still active, then we need to wait for the operation
            // to finish and the app, whether it exists or not (it may have crashed),
            // still owns this capsule. If the HMAC is not active, then
            // we need to verify that that application still exists, and remove
            // it as owner if not.
            if self.active.get() {
                owning_app == processid
            } else {
                // Check the app still exists.
                //
                // If the `.enter()` succeeds, then the app is still valid, and
                // we can check if the owning app matches the one that called
                // the command. If the `.enter()` fails, then the owning app no
                // longer exists and we return `true` to signify the
                // "or_nonexistant" case.
                self.apps
                    .enter(owning_app, |_, _| owning_app == processid)
                    .unwrap_or(true)
            }
        });

        let app_match = self.processid.map_or(false, |owning_app| {
            // We have recorded that an app has ownership of the HMAC.

            // If the HMAC is still active, then we need to wait for the operation
            // to finish and the app, whether it exists or not (it may have crashed),
            // still owns this capsule. If the HMAC is not active, then
            // we need to verify that that application still exists, and remove
            // it as owner if not.
            if self.active.get() {
                owning_app == processid
            } else {
                // Check the app still exists.
                //
                // If the `.enter()` succeeds, then the app is still valid, and
                // we can check if the owning app matches the one that called
                // the command. If the `.enter()` fails, then the owning app no
                // longer exists and we return `true` to signify the
                // "or_nonexistant" case.
                self.apps
                    .enter(owning_app, |_, _| owning_app == processid)
                    .unwrap_or(true)
            }
        });

        // Try the commands where we want to start an operation *not* entered in
        // an app grant first.
        if match_or_empty_or_nonexistant
            && (command_num == 1 || command_num == 2 || command_num == 4)
        {
            self.processid.set(processid);

            let _ = self.apps.enter(processid, |app, _| {
                if command_num == 1 {
                    // run
                    // Use key and data to compute hash
                    // This will trigger a callback once the digest is generated
                    app.op.set(Some(UserSpaceOp::Run));
                } else if command_num == 2 {
                    // update
                    // Input key and data, don't compute final hash yet
                    // This will trigger a callback once the data has been added.
                    app.op.set(Some(UserSpaceOp::Update));
                } else if command_num == 4 {
                    // verify
                    // Use key and data to compute hash and comapre it against
                    // the digest
                    app.op.set(Some(UserSpaceOp::Verify));
                }
            });

            return if let Err(e) = self.run() {
                self.hmac.clear_data();
                self.processid.clear();
                self.check_queue();
                CommandReturn::failure(e)
            } else {
                CommandReturn::success()
            };
        }

        self.apps
            .enter(processid, |app, kernel_data| {
                match command_num {
                    // set_algorithm
                    0 => {
                        match data1 {
                            // SHA256
                            0 => {
                                app.sha_operation = Some(ShaOperation::Sha256);
                                CommandReturn::success()
                            }
                            // SHA384
                            1 => {
                                app.sha_operation = Some(ShaOperation::Sha384);
                                CommandReturn::success()
                            }
                            // SHA512
                            2 => {
                                app.sha_operation = Some(ShaOperation::Sha512);
                                CommandReturn::success()
                            }
                            _ => CommandReturn::failure(ErrorCode::NOSUPPORT),
                        }
                    }

                    // run
                    1 => {
                        // There is an active app, so queue this request (if possible).
                        if app.pending_run_app.is_some() {
                            // No more room in the queue, nowhere to store this
                            // request.
                            CommandReturn::failure(ErrorCode::NOMEM)
                        } else {
                            // We can store this, so lets do it.
                            app.pending_run_app = Some(processid);
                            app.op.set(Some(UserSpaceOp::Run));
                            CommandReturn::success()
                        }
                    }

                    // update
                    2 => {
                        // There is an active app, so queue this request (if possible).
                        if app.pending_run_app.is_some() {
                            // No more room in the queue, nowhere to store this
                            // request.
                            CommandReturn::failure(ErrorCode::NOMEM)
                        } else {
                            // We can store this, so lets do it.
                            app.pending_run_app = Some(processid);
                            app.op.set(Some(UserSpaceOp::Update));
                            CommandReturn::success()
                        }
                    }

                    // finish
                    // Compute final hash yet, useful after a update command
                    3 => {
                        if app_match {
                            if let Err(e) = self.calculate_digest() {
                                kernel_data
                                    .schedule_upcall(
                                        0,
                                        (kernel::errorcode::into_statuscode(e.into()), 0, 0),
                                    )
                                    .ok();
                            }
                            CommandReturn::success()
                        } else {
                            // We don't queue this request, the user has to call
                            // `update` first.
                            CommandReturn::failure(ErrorCode::OFF)
                        }
                    }

                    // verify
                    4 => {
                        // There is an active app, so queue this request (if possible).
                        if app.pending_run_app.is_some() {
                            // No more room in the queue, nowhere to store this
                            // request.
                            CommandReturn::failure(ErrorCode::NOMEM)
                        } else {
                            // We can store this, so lets do it.
                            app.pending_run_app = Some(processid);
                            app.op.set(Some(UserSpaceOp::Verify));
                            CommandReturn::success()
                        }
                    }

                    // verify_finish
                    // Use key and data to compute hash and compare it against
                    // the digest, useful after a update command
                    5 => {
                        if app_match {
                            let _ = kernel_data
                                .get_readonly_processbuffer(ro_allow::COMPARE)
                                .and_then(|compare| {
                                    compare.enter(|compare| {
                                        let mut static_buffer_len = 0;
                                        self.dest_buffer.map(|buf| {
                                            // Determine the size of the static buffer we have
                                            static_buffer_len = buf.len();

                                            if static_buffer_len > compare.len() {
                                                static_buffer_len = compare.len()
                                            }

                                            self.data_copied.set(static_buffer_len);

                                            // Copy the data into the static buffer
                                            compare[..static_buffer_len]
                                                .copy_to_slice(&mut buf[..static_buffer_len]);
                                        });
                                    })
                                });

                            if let Err(e) = self.verify_digest() {
                                kernel_data
                                    .schedule_upcall(1, (into_statuscode(e.into()), 0, 0))
                                    .ok();
                            }
                            CommandReturn::success()
                        } else {
                            // We don't queue this request, the user has to call
                            // `update` first.
                            CommandReturn::failure(ErrorCode::OFF)
                        }
                    }

                    // default
                    _ => CommandReturn::failure(ErrorCode::NOSUPPORT),
                }
            })
            .unwrap_or_else(|err| err.into())
    }

    fn allocate_grant(&self, processid: ProcessId) -> Result<(), kernel::process::Error> {
        self.apps.enter(processid, |_, _| {})
    }
}

#[derive(Copy, Clone, PartialEq)]
enum UserSpaceOp {
    Run,
    Update,
    Verify,
}

#[derive(Default)]
pub struct App {
    pending_run_app: Option<ProcessId>,
    sha_operation: Option<ShaOperation>,
    op: Cell<Option<UserSpaceOp>>,
}