mirror of
https://github.com/SerenityOS/serenity
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f18e7659a6
If we don't set FP and LR to 0, the Kernel might not stop generating backtraces when it reaches `_start`'s stack frame, and might continue by reading garbage memory instead. This leads to a kernel panic, as SafeMem access faults aren't handled properly in the AArch64 kernel yet. We might want to ensure that the kernel zeroes out all registers when a new process is created.
120 lines
3.5 KiB
C++
120 lines
3.5 KiB
C++
/*
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* Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <LibELF/AuxiliaryVector.h>
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#include <LibELF/DynamicLinker.h>
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#include <LibELF/Relocation.h>
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#include <sys/internals.h>
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#include <unistd.h>
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char* __static_environ[] = { nullptr }; // We don't get the environment without some libc workarounds..
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static void init_libc()
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{
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environ = __static_environ;
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__environ_is_malloced = false;
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__stdio_is_initialized = false;
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// Initialise the copy of libc included statically in Loader.so,
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// initialisation of the dynamic libc.so is done by the DynamicLinker
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__libc_init();
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}
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static void perform_self_relocations(auxv_t* auxvp)
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{
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// We need to relocate ourselves.
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// (these relocations seem to be generated because of our vtables)
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FlatPtr base_address = 0;
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bool found_base_address = false;
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for (; auxvp->a_type != AT_NULL; ++auxvp) {
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if (auxvp->a_type == ELF::AuxiliaryValue::BaseAddress) {
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base_address = auxvp->a_un.a_val;
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found_base_address = true;
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}
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}
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VERIFY(found_base_address);
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if (!ELF::perform_relative_relocations(base_address))
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exit(1);
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}
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static void display_help()
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{
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char const message[] =
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R"(You have invoked `Loader.so'. This is the helper program for programs that
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use shared libraries. Special directives embedded in executables tell the
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kernel to load this program.
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This helper program loads the shared libraries needed by the program,
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prepares the program to run, and runs it. You do not need to invoke
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this helper program directly.
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)";
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fprintf(stderr, "%s", message);
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}
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extern "C" {
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// The compiler expects a previous declaration
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void _start(int, char**, char**) __attribute__((used));
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void _entry(int, char**, char**) __attribute__((used));
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NAKED void _start(int, char**, char**)
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{
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#if ARCH(AARCH64)
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// Make sure backtrace computation stops here by setting FP and LR to 0.
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// FIXME: The kernel should ensure that registers are zeroed on program start
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asm(
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"mov x29, 0\n"
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"mov x30, 0\n"
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"bl _entry\n");
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#else
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asm(
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"push $0\n"
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"jmp _entry@plt\n");
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#endif
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}
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void _entry(int argc, char** argv, char** envp)
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{
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char** env;
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for (env = envp; *env; ++env) {
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}
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auxv_t* auxvp = (auxv_t*)++env;
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perform_self_relocations(auxvp);
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init_libc();
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int main_program_fd = -1;
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DeprecatedString main_program_path;
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bool is_secure = false;
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for (; auxvp->a_type != AT_NULL; ++auxvp) {
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if (auxvp->a_type == ELF::AuxiliaryValue::ExecFileDescriptor) {
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main_program_fd = auxvp->a_un.a_val;
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}
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if (auxvp->a_type == ELF::AuxiliaryValue::ExecFilename) {
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main_program_path = (char const*)auxvp->a_un.a_ptr;
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}
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if (auxvp->a_type == ELF::AuxiliaryValue::Secure) {
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is_secure = auxvp->a_un.a_val == 1;
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}
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}
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if (main_program_path == "/usr/lib/Loader.so"sv) {
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// We've been invoked directly as an executable rather than as the
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// ELF interpreter for some other binary. In the future we may want
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// to support launching a program directly from the dynamic loader
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// like ld.so on Linux.
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display_help();
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_exit(1);
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}
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VERIFY(main_program_fd >= 0);
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VERIFY(!main_program_path.is_empty());
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ELF::DynamicLinker::linker_main(move(main_program_path), main_program_fd, is_secure, argc, argv, envp);
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VERIFY_NOT_REACHED();
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}
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}
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