Magisk/native/jni/magiskboot/dtb.cpp

#include <unistd.h>
#include <sys/mman.h>
#include <bitset>
#include <vector>
#include <map>

#include <utils.hpp>

#include "magiskboot.hpp"
#include "dtb.hpp"
extern "C" {
#include <libfdt.h>
}

using namespace std;

constexpr int MAX_DEPTH = 32;
static bitset<MAX_DEPTH> depth_set;

static void pretty_node(int depth) {
    if (depth == 0)
        return;

    for (int i = 0; i < depth - 1; ++i)
        printf(depth_set[i] ? "│   " : "    ");

    printf(depth_set[depth - 1] ? "├── " : "└── ");
}

static void pretty_prop(int depth) {
    for (int i = 0; i < depth; ++i)
        printf(depth_set[i] ? "│   " : "    ");

    printf(depth_set[depth] ? "│  " : "   ");
}

static void print_node(const void *fdt, int node = 0, int depth = 0) {
    // Print node itself
    pretty_node(depth);
    printf("#%d: %s\n", node, fdt_get_name(fdt, node, nullptr));

    // Print properties
    depth_set[depth] = fdt_first_subnode(fdt, node) >= 0;
    int prop;
    fdt_for_each_property_offset(prop, fdt, node) {
        pretty_prop(depth);
        int size;
        const char *name;
        auto value = static_cast<const char *>(fdt_getprop_by_offset(fdt, prop, &name, &size));

        bool is_str = !(size > 1 && value[0] == 0);
        if (is_str) {
            // Scan through value to see if printable
            for (int i = 0; i < size; ++i) {
                char c = value[i];
                if (i == size - 1) {
                    // Make sure null terminate
                    is_str = c == '\0';
                } else if ((c > 0 && c < 32) || c >= 127) {
                    is_str = false;
                    break;
                }
            }
        }

        if (is_str) {
            printf("[%s]: [%s]\n", name, value);
        } else {
            printf("[%s]: <bytes>(%d)\n", name, size);
        }
    }

    // Recursive
    if (depth_set[depth]) {
        int child;
        int prev = -1;
        fdt_for_each_subnode(child, fdt, node) {
            if (prev >= 0)
                print_node(fdt, prev, depth + 1);
            prev = child;
        }
        depth_set[depth] = false;
        print_node(fdt, prev, depth + 1);
    }
}

static int find_fstab(const void *fdt, int node = 0) {
    if (fdt_get_name(fdt, node, nullptr) == "fstab"sv)
        return node;
    int child;
    fdt_for_each_subnode(child, fdt, node) {
        int fstab = find_fstab(fdt, child);
        if (fstab >= 0)
            return fstab;
    }
    return -1;
}

static void dtb_print(const char *file, bool fstab) {
    size_t size;
    uint8_t *dtb;
    fprintf(stderr, "Loading dtbs from [%s]\n", file);
    mmap_ro(file, dtb, size);
    // Loop through all the dtbs
    int dtb_num = 0;
    for (int i = 0; i < size; ++i) {
        if (memcmp(dtb + i, FDT_MAGIC_STR, 4) == 0) {
            auto fdt = dtb + i;
            if (fstab) {
                int node = find_fstab(fdt);
                if (node >= 0) {
                    fprintf(stderr, "Found fstab in dtb.%04d\n", dtb_num);
                    print_node(fdt, node);
                }
            } else {
                fprintf(stderr, "Printing dtb.%04d\n", dtb_num);
                print_node(fdt);
            }
            ++dtb_num;
            i += fdt_totalsize(fdt) - 1;
        }
    }
    fprintf(stderr, "\n");
    munmap(dtb, size);
}

static bool dtb_patch_rebuild(uint8_t *dtb, size_t dtb_sz, const char *file);

static bool dtb_patch(const char *file) {
    bool keep_verity = check_env("KEEPVERITY");
    bool have_system = false;
    vector<pair<char *, int>> flags_list;

    size_t size;
    uint8_t *dtb;
    fprintf(stderr, "Loading dtbs from [%s]\n", file);
    mmap_rw(file, dtb, size);
    run_finally f([=]{ munmap(dtb, size); });

    // First traverse through DTB to determine whether we need a rebuild
    int dtb_num = 0;
    for (int i = 0; i < size; ++i) {
        if (memcmp(dtb + i, FDT_MAGIC_STR, 4) == 0) {
            auto fdt = dtb + i;
            if (int fstab = find_fstab(fdt); fstab >= 0) {
                int node;
                fdt_for_each_subnode(node, fdt, fstab) {
                    const char *name = fdt_get_name(fdt, node, nullptr);
                    if (!keep_verity) {
                        int len;
                        char *value = (char *) fdt_getprop(fdt, node, "fsmgr_flags", &len);
                        flags_list.emplace_back(value, len);
                    }
                    if (name == "system"sv)
                        have_system = true;
                }
            }
            i += fdt_totalsize(fdt) - 1;
            ++dtb_num;
        }
    }

    if (!have_system) {
        // Patch in place with rw mmap
        bool patched = false;
        for (auto &[value, len] : flags_list)
            patched |= patch_verity(value, len) != len;
        return patched;
    } else {
        // Need to rebuild dtb due to additional props
        return dtb_patch_rebuild(dtb, size, file);
    }
}

int dtb_commands(int argc, char *argv[]) {
    char *dtb = argv[0];
    ++argv;
    --argc;

    if (argv[0] == "print"sv) {
        dtb_print(dtb, argc > 1 && argv[1] == "-f"sv);
        return 0;
    } else if (argv[0] == "patch"sv) {
        if (!dtb_patch(dtb))
            exit(1);
        return 0;
    } else {
        return 1;
    }
}

namespace {

struct fdt_blob {
    void *fdt;
    uint32_t offset;
    uint32_t len;
};

}

static bool fdt_patch(void *fdt) {
    int fstab = find_fstab(fdt);
    if (fstab < 0)
        return false;
    bool modified = false;
    int node;
    fdt_for_each_subnode(node, fdt, fstab) {
        const char *name = fdt_get_name(fdt, node, nullptr);
        // Always patch verity if 2SI
        int len;
        auto value = (const char *) fdt_getprop(fdt, node, "fsmgr_flags", &len);
        string copy(value, len);
        uint32_t new_len = patch_verity(copy.data(), len);
        if (new_len != len) {
            modified = true;
            fdt_setprop(fdt, node, "fsmgr_flags", copy.data(), new_len);
        }
        if (name == "system"sv) {
            fprintf(stderr, "Setting [mnt_point] to [/system_root]\n");
            fdt_setprop_string(fdt, node, "mnt_point", "/system_root");
            modified = true;
        }
    }
    return modified;
}

#define MAX_FDT_GROWTH 256

template <class Table, class Header>
static bool dt_table_patch(const Header *hdr, const char *out) {
    map<uint32_t, fdt_blob> dtb_map;
    auto buf = reinterpret_cast<const uint8_t *>(hdr);
    auto tables = reinterpret_cast<const Table *>(buf + sizeof(Header));

    constexpr bool is_aosp = std::is_same_v<Header, dt_table_header>;

    // AOSP DTB store ints in big endian
    using endian_conv = uint32_t (*)(uint32_t);
    endian_conv be_to_le;
    endian_conv le_to_be;
    if constexpr (is_aosp) {
        be_to_le = fdt32_to_cpu;
        le_to_be = cpu_to_fdt32;
    } else {
        be_to_le = le_to_be = [](uint32_t x) { return x; };
    }

    // Collect all dtbs
    auto num_dtb = be_to_le(hdr->num_dtbs);
    for (int i = 0; i < num_dtb; ++i) {
        auto offset = be_to_le(tables[i].offset);
        if (dtb_map.count(offset) == 0) {
            auto blob = buf + offset;
            uint32_t size = fdt_totalsize(blob);
            auto fdt = xmalloc(size + MAX_FDT_GROWTH);
            memcpy(fdt, blob, size);
            fdt_open_into(fdt, fdt, size + MAX_FDT_GROWTH);
            dtb_map[offset] = { fdt, offset };
        }
    }
    if (dtb_map.empty())
        return false;

    // Patch fdt
    bool modified = false;
    for (auto &[_, blob] : dtb_map)
        modified |= fdt_patch(blob.fdt);
    if (!modified)
        return false;

    unlink(out);
    int fd = xopen(out, O_RDWR | O_CREAT | O_CLOEXEC, 0644);

    // This value is only used if AOSP DTB
    uint32_t total_size = 0;

    // Copy headers and tables
    total_size += xwrite(fd, buf, dtb_map.begin()->first);

    // mmap rw to patch table values retroactively
    auto mmap_sz = lseek(fd, 0, SEEK_CUR);
    auto addr = (uint8_t *) xmmap(nullptr, mmap_sz, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

    // Guess alignment using gcd
    uint32_t align = 1;
    if constexpr (!is_aosp) {
        auto it = dtb_map.begin();
        align = (it++)->first;
        for (; it != dtb_map.end(); ++it)
            align = binary_gcd(align, it->first);
    }

    // Write dtbs
    for (auto &val : dtb_map) {
        val.second.offset = lseek(fd, 0, SEEK_CUR);
        auto fdt = val.second.fdt;
        fdt_pack(fdt);
        auto size = fdt_totalsize(fdt);
        total_size += xwrite(fd, fdt, size);
        if constexpr (!is_aosp) {
            val.second.len = do_align(size, align);
            write_zero(fd, align_off(lseek(fd, 0, SEEK_CUR), align));
        }
        free(fdt);
    }

    // Patch headers
    if constexpr (is_aosp) {
        auto hdr_rw = reinterpret_cast<Header *>(addr);
        hdr_rw->total_size = le_to_be(total_size);
    }
    auto tables_rw = reinterpret_cast<Table *>(addr + sizeof(Header));
    for (int i = 0; i < num_dtb; ++i) {
        auto &blob = dtb_map[be_to_le(tables_rw[i].offset)];
        tables_rw[i].offset = le_to_be(blob.offset);
        tables_rw[i].len = le_to_be(blob.len);
    }

    munmap(addr, mmap_sz);
    close(fd);

    return true;
}

static bool blob_patch(uint8_t *dtb, size_t dtb_sz, const char *out) {
    vector<uint8_t *> fdt_list;
    vector<uint32_t> padding_list;

    for (int i = 0; i < dtb_sz; ++i) {
        if (memcmp(dtb + i, FDT_MAGIC_STR, 4) == 0) {
            auto len = fdt_totalsize(dtb + i);
            auto fdt = static_cast<uint8_t *>(xmalloc(len + MAX_FDT_GROWTH));
            memcpy(fdt, dtb + i, len);
            fdt_pack(fdt);
            uint32_t padding = len - fdt_totalsize(fdt);
            padding_list.push_back(padding);
            fdt_open_into(fdt, fdt, len + MAX_FDT_GROWTH);
            fdt_list.push_back(fdt);
            i += len - 1;
        }
    }

    bool modified = false;
    for (auto fdt : fdt_list)
        modified |= fdt_patch(fdt);
    if (!modified)
        return false;

    unlink(out);
    int fd = xopen(out, O_WRONLY | O_CREAT | O_CLOEXEC, 0644);

    for (int i = 0; i < fdt_list.size(); ++i) {
        auto fdt = fdt_list[i];
        fdt_pack(fdt);
        // Only add padding back if it is anything meaningful
        if (padding_list[i] > 4) {
            auto len = fdt_totalsize(fdt);
            fdt_set_totalsize(fdt, len + padding_list[i]);
        }
        xwrite(fd, fdt, fdt_totalsize(fdt));
        free(fdt);
    }
    close(fd);

    return true;
}

#define MATCH(s) (memcmp(dtb, s, sizeof(s) - 1) == 0)

static bool dtb_patch_rebuild(uint8_t *dtb, size_t dtb_sz, const char *file) {
    if (MATCH(QCDT_MAGIC)) {
        auto hdr = reinterpret_cast<qcdt_hdr*>(dtb);
        switch (hdr->version) {
            case 1:
                fprintf(stderr, "QCDT v1\n");
                return dt_table_patch<qctable_v1>(hdr, file);
            case 2:
                fprintf(stderr, "QCDT v2\n");
                return dt_table_patch<qctable_v2>(hdr, file);
            case 3:
                fprintf(stderr, "QCDT v3\n");
                return dt_table_patch<qctable_v3>(hdr, file);
            default:
                return false;
        }
    } else if (MATCH(DTBH_MAGIC)) {
        auto hdr = reinterpret_cast<dtbh_hdr *>(dtb);
        switch (hdr->version) {
            case 2:
                fprintf(stderr, "DTBH v2\n");
                return dt_table_patch<bhtable_v2>(hdr, file);
            default:
                return false;
        }
    } else if (MATCH(PXADT_MAGIC)) {
        auto hdr = reinterpret_cast<pxadt_hdr *>(dtb);
        switch (hdr->version) {
            case 1:
                fprintf(stderr, "PXA-DT v1\n");
                return dt_table_patch<pxatable_v1>(hdr, file);
            default:
                return false;
        }
    } else if (MATCH(PXA19xx_MAGIC)) {
        auto hdr = reinterpret_cast<pxa19xx_hdr *>(dtb);
        switch (hdr->version) {
            case 1:
                fprintf(stderr, "PXA-19xx v1\n");
                return dt_table_patch<pxatable_v1>(hdr, file);
            default:
                return false;
        }
    } else if (MATCH(SPRD_MAGIC)) {
        auto hdr = reinterpret_cast<sprd_hdr *>(dtb);
        switch (hdr->version) {
            case 1:
                fprintf(stderr, "SPRD v1\n");
                return dt_table_patch<sprdtable_v1>(hdr, file);
            default:
                return false;
        }
    } else if (MATCH(DT_TABLE_MAGIC)) {
        auto hdr = reinterpret_cast<dt_table_header *>(dtb);
        switch (hdr->version) {
            case 0:
                fprintf(stderr, "DT_TABLE v0\n");
                return dt_table_patch<dt_table_entry>(hdr, file);
            default:
                return false;
        }
    } else {
        return blob_patch(dtb, dtb_sz, file);
    }
}