path: root/Userland/Libraries/LibELF/DynamicObject.h

/*
 * Copyright (c) 2019-2020, Andrew Kaster <andrewdkaster@gmail.com>
 * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Assertions.h>
#include <AK/RefCounted.h>
#include <AK/String.h>
#include <Kernel/VirtualAddress.h>
#include <LibC/elf.h>

namespace ELF {

class DynamicObject : public RefCounted<DynamicObject> {
public:
    static NonnullRefPtr<DynamicObject> create(const String& filename, VirtualAddress base_address, VirtualAddress dynamic_section_address);

    ~DynamicObject();
    void dump() const;

    class DynamicEntry;
    class Section;
    class RelocationSection;
    class Symbol;
    class Relocation;
    class HashSection;

    class DynamicEntry {
    public:
        explicit DynamicEntry(const Elf32_Dyn& dyn)
            : m_dyn(dyn)
        {
        }

        ~DynamicEntry() { }

        Elf32_Sword tag() const { return m_dyn.d_tag; }
        Elf32_Addr ptr() const { return m_dyn.d_un.d_ptr; }
        Elf32_Word val() const { return m_dyn.d_un.d_val; }

    private:
        const Elf32_Dyn& m_dyn;
    };

    class Symbol {
    public:
        Symbol(const DynamicObject& dynamic, unsigned index, const Elf32_Sym& sym)
            : m_dynamic(dynamic)
            , m_sym(sym)
            , m_index(index)
        {
        }

        StringView name() const { return m_dynamic.symbol_string_table_string(m_sym.st_name); }
        const char* raw_name() const { return m_dynamic.raw_symbol_string_table_string(m_sym.st_name); }
        unsigned section_index() const { return m_sym.st_shndx; }
        unsigned value() const { return m_sym.st_value; }
        unsigned size() const { return m_sym.st_size; }
        unsigned index() const { return m_index; }
        unsigned type() const { return ELF32_ST_TYPE(m_sym.st_info); }
        unsigned bind() const { return ELF32_ST_BIND(m_sym.st_info); }

        bool is_undefined() const { return section_index() == 0; }

        VirtualAddress address() const
        {
            if (m_dynamic.elf_is_dynamic())
                return m_dynamic.base_address().offset(value());
            return VirtualAddress { value() };
        }
        const DynamicObject& object() const { return m_dynamic; }

    private:
        const DynamicObject& m_dynamic;
        const Elf32_Sym& m_sym;
        const unsigned m_index;
    };

    class Section {
    public:
        Section(const DynamicObject& dynamic, unsigned section_offset, unsigned section_size_bytes, unsigned entry_size, const StringView& name)
            : m_dynamic(dynamic)
            , m_section_offset(section_offset)
            , m_section_size_bytes(section_size_bytes)
            , m_entry_size(entry_size)
            , m_name(name)
        {
        }
        ~Section() { }

        StringView name() const { return m_name; }
        unsigned offset() const { return m_section_offset; }
        unsigned size() const { return m_section_size_bytes; }
        unsigned entry_size() const { return m_entry_size; }
        unsigned entry_count() const
        {
            return !entry_size() ? 0 : size() / entry_size();
        }
        VirtualAddress address() const
        {
            return m_dynamic.base_address().offset(m_section_offset);
        }

    protected:
        friend class RelocationSection;
        friend class HashSection;
        const DynamicObject& m_dynamic;
        unsigned m_section_offset;
        unsigned m_section_size_bytes;
        unsigned m_entry_size;
        StringView m_name;
    };

    class RelocationSection : public Section {
    public:
        explicit RelocationSection(const Section& section)
            : Section(section.m_dynamic, section.m_section_offset, section.m_section_size_bytes, section.m_entry_size, section.m_name)
        {
        }
        unsigned relocation_count() const { return entry_count(); }
        Relocation relocation(unsigned index) const;
        Relocation relocation_at_offset(unsigned offset) const;
        template<typename F>
        void for_each_relocation(F) const;
    };

    class Relocation {
    public:
        Relocation(const DynamicObject& dynamic, const Elf32_Rel& rel, unsigned offset_in_section)
            : m_dynamic(dynamic)
            , m_rel(rel)
            , m_offset_in_section(offset_in_section)
        {
        }

        ~Relocation() { }

        unsigned offset_in_section() const { return m_offset_in_section; }
        unsigned offset() const { return m_rel.r_offset; }
        unsigned type() const { return ELF32_R_TYPE(m_rel.r_info); }
        unsigned symbol_index() const { return ELF32_R_SYM(m_rel.r_info); }
        Symbol symbol() const { return m_dynamic.symbol(symbol_index()); }
        VirtualAddress address() const
        {
            if (m_dynamic.elf_is_dynamic())
                return m_dynamic.base_address().offset(offset());
            return VirtualAddress { offset() };
        }

    private:
        const DynamicObject& m_dynamic;
        const Elf32_Rel& m_rel;
        const unsigned m_offset_in_section;
    };

    enum class HashType {
        SYSV,
        GNU
    };

    class HashSection : public Section {
    public:
        HashSection(const Section& section, HashType hash_type)
            : Section(section.m_dynamic, section.m_section_offset, section.m_section_size_bytes, section.m_entry_size, section.m_name)
            , m_hash_type(hash_type)
        {
        }

        Optional<Symbol> lookup_symbol(const StringView& name, u32 gnu_hash, u32 sysv_hash) const
        {
            if (m_hash_type == HashType::SYSV)
                return lookup_sysv_symbol(name, sysv_hash);
            return lookup_gnu_symbol(name, gnu_hash);
        }

    private:
        Optional<Symbol> lookup_sysv_symbol(const StringView& name, u32 hash_value) const;
        Optional<Symbol> lookup_gnu_symbol(const StringView& name, u32 hash) const;

        HashType m_hash_type {};
    };

    unsigned symbol_count() const { return m_symbol_count; }

    Symbol symbol(unsigned) const;

    typedef void (*InitializationFunction)();

    bool has_init_section() const { return m_init_offset != 0; }
    bool has_init_array_section() const { return m_init_array_offset != 0; }
    Section init_section() const;
    InitializationFunction init_section_function() const;
    Section fini_section() const;
    Section init_array_section() const;
    Section fini_array_section() const;

    HashSection hash_section() const
    {
        auto section_name = m_hash_type == HashType::SYSV ? "DT_HASH"sv : "DT_GNU_HASH"sv;

        return HashSection(Section(*this, m_hash_table_offset, 0, 0, section_name), m_hash_type);
    }

    RelocationSection relocation_section() const;
    RelocationSection plt_relocation_section() const;

    bool should_process_origin() const { return m_dt_flags & DF_ORIGIN; }
    bool requires_symbolic_symbol_resolution() const { return m_dt_flags & DF_SYMBOLIC; }
    // Text relocations meaning: we need to edit the .text section which is normally mapped PROT_READ
    bool has_text_relocations() const { return m_dt_flags & DF_TEXTREL; }
    bool must_bind_now() const { return m_dt_flags & DF_BIND_NOW; }
    bool has_static_thread_local_storage() const { return m_dt_flags & DF_STATIC_TLS; }

    bool has_plt() const { return m_procedure_linkage_table_offset.has_value(); }
    VirtualAddress plt_got_base_address() const { return m_base_address.offset(m_procedure_linkage_table_offset.value()); }
    VirtualAddress base_address() const { return m_base_address; }

    const String& filename() const { return m_filename; }

    StringView rpath() const { return m_has_rpath ? symbol_string_table_string(m_rpath_index) : StringView {}; }
    StringView runpath() const { return m_has_runpath ? symbol_string_table_string(m_runpath_index) : StringView {}; }
    StringView soname() const { return m_has_soname ? symbol_string_table_string(m_soname_index) : StringView {}; }

    Optional<FlatPtr> tls_offset() const { return m_tls_offset; }
    Optional<FlatPtr> tls_size() const { return m_tls_size; }
    void set_tls_offset(FlatPtr offset) { m_tls_offset = offset; }
    void set_tls_size(FlatPtr size) { m_tls_size = size; }

    Elf32_Half program_header_count() const;
    const Elf32_Phdr* program_headers() const;

    template<typename F>
    void for_each_needed_library(F) const;

    template<typename F>
    void for_each_initialization_array_function(F f) const;

    template<typename F>
    void for_each_dynamic_entry(F) const;

    template<typename F>
    void for_each_symbol(F) const;

    struct SymbolLookupResult {
        FlatPtr value { 0 };
        VirtualAddress address;
        unsigned bind { STB_LOCAL };
        const ELF::DynamicObject* dynamic_object { nullptr }; // The object in which the symbol is defined
    };

    Optional<SymbolLookupResult> lookup_symbol(const StringView& name) const;
    Optional<SymbolLookupResult> lookup_symbol(const StringView& name, u32 gnu_hash, u32 sysv_hash) const;

    // Will be called from _fixup_plt_entry, as part of the PLT trampoline
    VirtualAddress patch_plt_entry(u32 relocation_offset);

    bool elf_is_dynamic() const { return m_is_elf_dynamic; }

private:
    explicit DynamicObject(const String& filename, VirtualAddress base_address, VirtualAddress dynamic_section_address);

    StringView symbol_string_table_string(Elf32_Word) const;
    const char* raw_symbol_string_table_string(Elf32_Word) const;
    void parse();

    String m_filename;

    VirtualAddress m_base_address;
    VirtualAddress m_dynamic_address;
    VirtualAddress m_elf_base_address;

    unsigned m_symbol_count { 0 };

    // Begin Section information collected from DT_* entries
    FlatPtr m_init_offset { 0 };
    FlatPtr m_fini_offset { 0 };

    FlatPtr m_init_array_offset { 0 };
    size_t m_init_array_size { 0 };
    FlatPtr m_fini_array_offset { 0 };
    size_t m_fini_array_size { 0 };

    FlatPtr m_hash_table_offset { 0 };
    HashType m_hash_type { HashType::SYSV };

    FlatPtr m_string_table_offset { 0 };
    size_t m_size_of_string_table { 0 };
    FlatPtr m_symbol_table_offset { 0 };
    size_t m_size_of_symbol_table_entry { 0 };

    Elf32_Sword m_procedure_linkage_table_relocation_type { -1 };
    FlatPtr m_plt_relocation_offset_location { 0 }; // offset of PLT relocations, at end of relocations
    size_t m_size_of_plt_relocation_entry_list { 0 };
    Optional<FlatPtr> m_procedure_linkage_table_offset;

    // NOTE: We'll only ever either RELA or REL entries, not both (thank god)
    // NOTE: The x86 ABI will only ever genrerate REL entries.
    size_t m_number_of_relocations { 0 };
    size_t m_size_of_relocation_entry { 0 };
    size_t m_size_of_relocation_table { 0 };
    FlatPtr m_relocation_table_offset { 0 };
    bool m_is_elf_dynamic { false };

    // DT_FLAGS
    Elf32_Word m_dt_flags { 0 };

    bool m_has_soname { false };
    Elf32_Word m_soname_index { 0 }; // Index into dynstr table for SONAME
    bool m_has_rpath { false };
    Elf32_Word m_rpath_index { 0 }; // Index into dynstr table for RPATH
    bool m_has_runpath { false };
    Elf32_Word m_runpath_index { 0 }; // Index into dynstr table for RUNPATH

    Optional<FlatPtr> m_tls_offset;
    Optional<FlatPtr> m_tls_size;
    // End Section information from DT_* entries
};

template<typename F>
inline void DynamicObject::RelocationSection::for_each_relocation(F func) const
{
    for (unsigned i = 0; i < relocation_count(); ++i) {
        const auto reloc = relocation(i);
        if (reloc.type() == 0)
            continue;
        if (func(reloc) == IterationDecision::Break)
            break;
    }
}

template<typename F>
inline void DynamicObject::for_each_symbol(F func) const
{
    for (unsigned i = 0; i < symbol_count(); ++i) {
        if (func(symbol(i)) == IterationDecision::Break)
            break;
    }
}

template<typename F>
inline void DynamicObject::for_each_dynamic_entry(F func) const
{
    auto* dyns = reinterpret_cast<const Elf32_Dyn*>(m_dynamic_address.as_ptr());
    for (unsigned i = 0;; ++i) {
        auto&& dyn = DynamicEntry(dyns[i]);
        if (dyn.tag() == DT_NULL)
            break;
        if (func(dyn) == IterationDecision::Break)
            break;
    }
}
template<typename F>
inline void DynamicObject::for_each_needed_library(F func) const
{
    for_each_dynamic_entry([func, this](auto entry) {
        if (entry.tag() != DT_NEEDED)
            return IterationDecision::Continue;
        Elf32_Word offset = entry.val();
        StringView name { (const char*)(m_base_address.offset(m_string_table_offset).offset(offset)).as_ptr() };
        if (func(StringView(name)) == IterationDecision::Break)
            return IterationDecision::Break;
        return IterationDecision::Continue;
    });
}

template<typename F>
void DynamicObject::for_each_initialization_array_function(F f) const
{
    if (!has_init_array_section())
        return;
    FlatPtr init_array = (FlatPtr)init_array_section().address().as_ptr();
    for (size_t i = 0; i < (m_init_array_size / sizeof(void*)); ++i) {
        InitializationFunction current = ((InitializationFunction*)(init_array))[i];
        f(current);
    }
}

} // end namespace ELF