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Support bpf2bpf calls from ELF files
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Signed-off-by: Dave Thaler <[email protected]>
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@dthaler
dthaler committed Sep 27, 2024
1 parent 4907f1b commit 271112f
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Showing 2 changed files with 84 additions and 11 deletions.
88 changes: 77 additions & 11 deletions src/asm_files.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ bool is_map_section(const std::string& name) {
return name == "maps" || (name.length() > 5 && name.compare(0, maps_prefix.length(), maps_prefix) == 0);
}

std::tuple<string, ELFIO::Elf_Half> get_symbol_name_and_section_index(ELFIO::const_symbol_section_accessor& symbols,
std::tuple<string, ELFIO::Elf_Half> get_symbol_name_and_section_index(const ELFIO::const_symbol_section_accessor& symbols,
ELFIO::Elf_Xword index) {
string symbol_name;
ELFIO::Elf64_Addr value{};
Expand All @@ -74,7 +74,7 @@ std::tuple<string, ELFIO::Elf_Half> get_symbol_name_and_section_index(ELFIO::con
}

std::tuple<ELFIO::Elf64_Addr, unsigned char> get_value(const ELFIO::const_symbol_section_accessor& symbols,
ELFIO::Elf_Word index) {
ELFIO::Elf_Xword index) {
string symbol_name;
ELFIO::Elf64_Addr value{};
ELFIO::Elf_Xword size{};
Expand Down Expand Up @@ -162,12 +162,6 @@ std::tuple<string, ELFIO::Elf_Xword> get_program_name_and_size(ELFIO::section& s
return {program_name, size};
}

void relocate_function(ebpf_inst& inst, ELFIO::Elf64_Addr offset, ELFIO::Elf_Word index,
const ELFIO::const_symbol_section_accessor& symbols) {
auto [relocation_offset, relocation_type] = get_value(symbols, index);
inst.imm = ((relocation_offset - offset) / sizeof(ebpf_inst)) - 1;
}

void relocate_map(ebpf_inst& inst, const std::string& symbol_name,
const std::variant<size_t, std::map<std::string, size_t>>& map_record_size_or_map_offsets,
const program_info& info, ELFIO::Elf64_Addr offset, ELFIO::Elf_Word index,
Expand Down Expand Up @@ -205,6 +199,54 @@ void relocate_map(ebpf_inst& inst, const std::string& symbol_name,
}
}

struct function_relocation {
size_t prog_index{}; // Index of source program in vector of raw programs.
ELFIO::Elf_Xword source_offset{}; // Instruction offset in source section of source instruction.
ELFIO::Elf_Word relocation_entry_index{};
std::string target_function_name;
};

static void append_subprogram(raw_program& prog, ELFIO::section* subprogram_section,
ELFIO::const_symbol_section_accessor& symbols, std::string symbol_name) {
// Find subprogram by name.
for (ELFIO::Elf_Xword subprogram_offset = 0; subprogram_offset < subprogram_section->get_size();) {
auto [subprogram_name, subprogram_size] =
get_program_name_and_size(*subprogram_section, subprogram_offset, symbols);
if (subprogram_name == symbol_name) {
// Append subprogram instructions to the main program.
auto subprogram = vector_of<ebpf_inst>(subprogram_section->get_data() + subprogram_offset, subprogram_size);
prog.prog.insert(prog.prog.end(), subprogram.begin(), subprogram.end());
return;
}
subprogram_offset += subprogram_size;
}
assert(false);
}

static void append_subprograms(raw_program& prog, vector<raw_program>& res, vector<function_relocation>& function_relocations, ELFIO::elfio& reader,
ELFIO::const_symbol_section_accessor& symbols) {
// Perform function relocations and fill in the inst.imm values of CallLocal instructions.
std::map<std::string, ELFIO::Elf_Xword> subprogram_offsets;
for (auto& reloc : function_relocations) {
if (res[reloc.prog_index].function_name != prog.function_name) {
continue;
}

// Check whether we already appended the target program, and append it if not.
if (subprogram_offsets.find(reloc.target_function_name) == subprogram_offsets.end()) {
subprogram_offsets[reloc.target_function_name] = prog.prog.size();

auto [symbol_name, section_index] = get_symbol_name_and_section_index(symbols, reloc.relocation_entry_index);
ELFIO::section* subprogram_section = reader.sections[section_index];
append_subprogram(prog, subprogram_section, symbols, symbol_name);
}

// Fill in the PC offset into the imm field of the CallLocal instruction.
ELFIO::Elf_Xword target_offset = subprogram_offsets[reloc.target_function_name];
prog.prog[reloc.source_offset].imm = (int32_t)(target_offset - reloc.source_offset - 1);
}
}

vector<raw_program> read_elf(std::istream& input_stream, const std::string& path, const std::string& desired_section,
const ebpf_verifier_options_t* options, const ebpf_platform_t* platform) {
if (options == nullptr) {
Expand Down Expand Up @@ -298,6 +340,8 @@ vector<raw_program> read_elf(std::istream& input_stream, const std::string& path
vector<raw_program> res;
vector<string> unresolved_symbols;

std::map<std::string, raw_program&> segment_to_program;
vector<function_relocation> function_relocations;
for (const auto& section : reader.sections) {
const string name = section->get_name();
if (!desired_section.empty() && name != desired_section) {
Expand All @@ -322,6 +366,13 @@ vector<raw_program> read_elf(std::istream& input_stream, const std::string& path
program_name,
vector_of<ebpf_inst>(section->get_data() + program_offset, program_size),
info};

// We will need to recursively append any subprograms called, but only once
// for each subprogram no matter how many times called. So initialize a set
// to hold the list of subprogram names included.
std::set<string> subprograms{};
subprograms.insert(program_name);

auto prelocs = reader.sections[string(".rel") + name];
if (!prelocs) {
prelocs = reader.sections[string(".rela") + name];
Expand Down Expand Up @@ -357,11 +408,17 @@ vector<raw_program> read_elf(std::istream& input_stream, const std::string& path

auto [symbol_name, symbol_section_index] = get_symbol_name_and_section_index(symbols, index);

// Perform relocation for function symbols.
// Queue up relocation for function symbols.
if ((inst.opcode == INST_OP_CALL) && (inst.src == INST_CALL_LOCAL) &&
(reader.sections[symbol_section_index] == section.get())) {
relocate_function(inst, offset, index, symbols);
continue;
{
function_relocation fr{.prog_index = res.size(),
.source_offset = offset / sizeof(ebpf_inst),
.relocation_entry_index = index,
.target_function_name = symbol_name};
function_relocations.push_back(fr);
continue;
}
}

// Perform relocation for symbols located in the maps section.
Expand All @@ -377,10 +434,19 @@ vector<raw_program> read_elf(std::istream& input_stream, const std::string& path
}
prog.line_info.resize(prog.prog.size());
res.push_back(prog);
segment_to_program.insert({res.back().function_name, res.back()});
program_offset += program_size;
}
}

// Now that we have all programs in the list, we can recursively append any subprograms
// to the calling programs. We have to keep them as programs themselves in case the caller
// wants to verify them separately, but we also have to append them if used as subprograms to
// allow the caller to be fully verified since inst.imm can only point into the same program.
for (auto& prog : res) {
append_subprograms(prog, res, function_relocations, reader, symbols);
}

// Below, only relocations of symbols located in the map sections are allowed,
// so if there are relocations there needs to be a maps section.
if (!unresolved_symbols.empty()) {
Expand Down
7 changes: 7 additions & 0 deletions src/test/test_verify.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,11 @@ FAIL_UNMARSHAL("invalid", "invalid-lddw.o", ".text")
VERIFY_PROGRAM(project, filename, section_name, program_name, nullptr, &g_ebpf_platform_linux, true); \
}

#define TEST_PROGRAM_REJECT(project, filename, section_name, program_name) \
TEST_CASE("./check ebpf-samples/" project "/" filename " " program_name, "[verify][samples][" project "]") { \
VERIFY_PROGRAM(project, filename, section_name, program_name, nullptr, &g_ebpf_platform_linux, false); \
}

#define TEST_SECTION_REJECT(project, filename, section) \
TEST_CASE("./check ebpf-samples/" project "/" filename " " section, "[verify][samples][" project "]") { \
VERIFY_SECTION(project, filename, section, nullptr, &g_ebpf_platform_linux, false); \
Expand Down Expand Up @@ -497,6 +502,8 @@ TEST_SECTION("raw_tracepoint/filler/sys_sendmsg_x")
TEST_SECTION("raw_tracepoint/filler/proc_startupdate_2")
TEST_SECTION("raw_tracepoint/filler/sys_recvfrom_x")
*/
TEST_PROGRAM_REJECT("build", "bpf2bpf.o", ".text", "plus1"); // Subprogram will fail verification.
TEST_PROGRAM("build", "bpf2bpf.o", ".text", "func"); // Subprogram can be called from main program.
TEST_SECTION("build", "byteswap.o", ".text")
TEST_SECTION("build", "stackok.o", ".text")
TEST_SECTION("build", "packet_start_ok.o", "xdp")
Expand Down

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