zircon/system/ulib/libzbi/zbi-zx.cpp

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <libzbi/zbi-zx.h>

#include <lib/zx/vmar.h>
#include <lib/zx/vmo.h>
#include <limits.h>
#include <string.h>
#include <zircon/assert.h>

#include <utility>

namespace zbi {

namespace {

size_t PageRound(size_t size) {
    return (size + PAGE_SIZE) & -(size_t)PAGE_SIZE;
}

}

zx_status_t ZbiVMO::Init(zx::vmo vmo) {
    vmo_ = std::move(vmo);
    auto status = vmo_.get_size(&capacity_);
    if (status == ZX_OK && capacity_ > 0) {
        status = Map();
    }
    return status;
}

zx::vmo ZbiVMO::Release() {
    Unmap();
    capacity_= 0;
    return std::move(vmo_);
}

ZbiVMO::~ZbiVMO() {
    Unmap();
}

zx_status_t ZbiVMO::Map() {
    uintptr_t mapping;
    auto status = zx::vmar::root_self()->map(
        0, vmo_, 0, capacity_, ZX_VM_PERM_READ | ZX_VM_PERM_WRITE,
        &mapping);
    if (status == ZX_OK) {
        base_ = reinterpret_cast<uint8_t*>(mapping);
    }
    return status;
}

void ZbiVMO::Unmap() {
    if (base_) {
        [[maybe_unused]] auto status =
            zx::vmar::root_self()->unmap(reinterpret_cast<uintptr_t>(base_),
                                         capacity_);
        ZX_DEBUG_ASSERT(status == ZX_OK);
        base_ = nullptr;
    }
}

zbi_result_t ZbiVMO::AppendSection(uint32_t length, uint32_t type,
                                   uint32_t extra, uint32_t flags,
                                   const void* payload) {
    void* dest;
    auto result = CreateSection(length, type, extra, flags, &dest);
    if (result == ZBI_RESULT_OK) {
        memcpy(dest, payload, length);
    }
    return result;
}

zbi_result_t ZbiVMO::CreateSection(uint32_t length, uint32_t type,
                                   uint32_t extra, uint32_t flags,
                                   void** payload) {
    auto result = Zbi::CreateSection(length, type, extra, flags, payload);
    if (result == ZBI_RESULT_TOO_BIG) {
        const size_t new_capacity =
            PageRound(Length() + sizeof(zbi_header_t) + length);
        ZX_DEBUG_ASSERT(new_capacity > capacity_);
        auto status = vmo_.set_size(new_capacity);
        if (status == ZX_OK) {
            Unmap();
            capacity_ = new_capacity;
            status = Map();
        }
        if (status == ZX_OK) {
            result = Zbi::CreateSection(length, type, extra, flags, payload);
        }
    }
    return result;
}

zbi_result_t ZbiVMO::SplitComplete(ZbiVMO* kernel, ZbiVMO* data) const {
    // First check that it's a proper complete ZBI.  After this it should be
    // safe to trust the headers (modulo racing modification of the original
    // VMO, which we can't help).
    auto result = CheckComplete();
    if (result != ZBI_RESULT_OK) {
        return result;
    }

    // First clone a VMO covering just the leading kernel portion of the ZBI.
    auto kernel_hdr = Header() + 1;
    const uint32_t kernel_size =
        static_cast<uint32_t>(sizeof(zbi_header_t) * 2) + kernel_hdr->length;
    const size_t kernel_vmo_size = PageRound(kernel_size);
    auto status = vmo_.create_child(ZX_VMO_CHILD_COPY_ON_WRITE,
                                    0, kernel_vmo_size, &kernel->vmo_);
    if (status != ZX_OK) {
        return ZBI_RESULT_TOO_BIG;
    }

    // Map it in.
    kernel->Unmap();                    // Just in case.
    kernel->capacity_ = kernel_vmo_size;
    status = kernel->Map();
    if (status != ZX_OK) {
        return ZBI_RESULT_TOO_BIG;
    }
    // Update the size in the copied container header.
    kernel->Header()->length =
        kernel_size - static_cast<uint32_t>(sizeof(zbi_header_t));

    // Now create (or clone if possible) a VMO for the remainder.
    const uint32_t data_payload_size = Length() - kernel_size;
    const size_t data_vmo_size = PageRound(
        data_payload_size + static_cast<uint32_t>(sizeof(zbi_header_t)));

    // If by some miracle the remainder is aligned exactly right, then
    // we can clone the trailing portion as well.
    bool clone = (kernel_size - sizeof(zbi_header_t)) % PAGE_SIZE == 0;
    status = clone ?
        vmo_.create_child(ZX_VMO_CHILD_COPY_ON_WRITE,
                          kernel_size - sizeof(zbi_header_t),
                          data_vmo_size, &data->vmo_) :
        vmo_.create(data_vmo_size, 0, &data->vmo_);
    if (status != ZX_OK) {
        return ZBI_RESULT_TOO_BIG;
    }

    // Map it in.
    data->Unmap();                      // Just in case.
    data->capacity_ = data_vmo_size;
    status = data->Map();
    if (status != ZX_OK) {
        return ZBI_RESULT_TOO_BIG;
    }

    // Fill in the header and data (if not already virtually copied).
    *data->Header() = (zbi_header_t)ZBI_CONTAINER_HEADER(data_payload_size);
    if (!clone) {
        memcpy(data->Payload(), Base() + kernel_size, data_payload_size);
    }

    return ZBI_RESULT_OK;
}

// C API wrapper.
zbi_result_t SplitCompleteWrapper(zx_handle_t zbi_vmo,
                                  zx_handle_t* kernel_vmo,
                                  zx_handle_t* data_vmo) {
    ZbiVMO zbi, kernel, data;
    auto status = zbi.Init(zx::vmo(zbi_vmo));
    if (status != ZX_OK) {
        return ZBI_RESULT_TOO_BIG;
    }
    auto result = zbi.SplitComplete(&kernel, &data);
    if (result == ZBI_RESULT_OK) {
        *kernel_vmo = kernel.vmo_.release();
        *data_vmo = data.vmo_.release();
    }
    return result;
}

zbi_result_t zbi_split_complete(zx_handle_t zbi_vmo,
                                zx_handle_t* kernel_vmo,
                                zx_handle_t* data_vmo) {
    return SplitCompleteWrapper(zbi_vmo, kernel_vmo, data_vmo);
}

}  // namespace zbi