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Kernel: Perform exec-into-new-image directly in sys$execve()

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This ensures that everything allocated on the stack in Process::exec()
gets cleaned up. We had a few leaks related to the parsing of shebang
(#!) executables that get fixed by this.
This commit is contained in:
Andreas Kling 2022-01-13 23:12:51 +01:00
parent c7dbe27781
commit 0e72b04e7d
Notes: sideshowbarker 2024-07-17 20:55:48 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/0e72b04e7d3
3 changed files with 39 additions and 44 deletions
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4
Kernel/Process.cpp
View file

@ -151,7 +151,9 @@ ErrorOr<NonnullRefPtr<Process>> Process::try_create_user_process(RefPtr<Thread>&
setup_description(1);
setup_description(2);
if (auto result = process->exec(move(path_string), move(arguments), move(environment)); result.is_error()) {
Thread* new_main_thread = nullptr;
u32 prev_flags = 0;
if (auto result = process->exec(move(path_string), move(arguments), move(environment), new_main_thread, prev_flags); result.is_error()) {
dbgln("Failed to exec {}: {}", path, result.error());
first_thread = nullptr;
return result.release_error();

2
Kernel/Process.h
View file

@ -438,7 +438,7 @@ public:
NonnullOwnPtrVector<KString> const& arguments() const { return m_arguments; };
NonnullOwnPtrVector<KString> const& environment() const { return m_environment; };
ErrorOr<void> exec(NonnullOwnPtr<KString> path, NonnullOwnPtrVector<KString> arguments, NonnullOwnPtrVector<KString> environment, int recursion_depth = 0);
ErrorOr<void> exec(NonnullOwnPtr<KString> path, NonnullOwnPtrVector<KString> arguments, NonnullOwnPtrVector<KString> environment, Thread*& new_main_thread, u32& prev_flags, int recursion_depth = 0);
ErrorOr<LoadResult> load(NonnullRefPtr<OpenFileDescription> main_program_description, RefPtr<OpenFileDescription> interpreter_description, const ElfW(Ehdr) & main_program_header);

77
Kernel/Syscalls/execve.cpp
View file

@ -777,7 +777,7 @@ ErrorOr<RefPtr<OpenFileDescription>> Process::find_elf_interpreter_for_executabl
return nullptr;
}
ErrorOr<void> Process::exec(NonnullOwnPtr<KString> path, NonnullOwnPtrVector<KString> arguments, NonnullOwnPtrVector<KString> environment, int recursion_depth)
ErrorOr<void> Process::exec(NonnullOwnPtr<KString> path, NonnullOwnPtrVector<KString> arguments, NonnullOwnPtrVector<KString> environment, Thread*& new_main_thread, u32& prev_flags, int recursion_depth)
{
if (recursion_depth > 2) {
dbgln("exec({}): SHENANIGANS! recursed too far trying to find #! interpreter", path);
@ -815,7 +815,7 @@ ErrorOr<void> Process::exec(NonnullOwnPtr<KString> path, NonnullOwnPtrVector<KSt
auto shebang_path = TRY(shebang_words.first().try_clone());
arguments.ptr_at(0) = move(path);
TRY(arguments.try_prepend(move(shebang_words)));
return exec(move(shebang_path), move(arguments), move(environment), ++recursion_depth);
return exec(move(shebang_path), move(arguments), move(environment), new_main_thread, prev_flags, ++recursion_depth);
}
// #2) ELF32 for i386
@ -829,43 +829,8 @@ ErrorOr<void> Process::exec(NonnullOwnPtr<KString> path, NonnullOwnPtrVector<KSt
return ENOEXEC;
}
// The bulk of exec() is done by do_exec(), which ensures that all locals
// are cleaned up by the time we yield-teleport below.
Thread* new_main_thread = nullptr;
u32 prev_flags = 0;
auto interpreter_description = TRY(find_elf_interpreter_for_executable(path->view(), *main_program_header, nread, metadata.size));
TRY(do_exec(move(description), move(arguments), move(environment), move(interpreter_description), new_main_thread, prev_flags, *main_program_header));
VERIFY_INTERRUPTS_DISABLED();
VERIFY(Processor::in_critical());
auto* current_thread = Thread::current();
if (current_thread == new_main_thread) {
{
// Make sure that `path` gets deleted before we teleport into the new process.
// If we don't do this, it will leak (since we never return from this function.)
OwnPtr<KString> path_deleter = move(path);
}
// We need to enter the scheduler lock before changing the state
// and it will be released after the context switch into that
// thread. We should also still be in our critical section
VERIFY(!g_scheduler_lock.is_locked_by_current_processor());
VERIFY(Processor::in_critical() == 1);
g_scheduler_lock.lock();
current_thread->set_state(Thread::State::Running);
Processor::assume_context(*current_thread, prev_flags);
VERIFY_NOT_REACHED();
}
// NOTE: This code path is taken in the non-syscall case, i.e when the kernel spawns
// a userspace process directly (such as /bin/SystemServer on startup)
if (prev_flags & 0x200)
sti();
Processor::leave_critical();
return {};
return do_exec(move(description), move(arguments), move(environment), move(interpreter_description), new_main_thread, prev_flags, *main_program_header);
}
ErrorOr<FlatPtr> Process::sys$execve(Userspace<const Syscall::SC_execve_params*> user_params)
@ -873,7 +838,7 @@ ErrorOr<FlatPtr> Process::sys$execve(Userspace<const Syscall::SC_execve_params*>
VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
TRY(require_promise(Pledge::exec));
// NOTE: Be extremely careful with allocating any kernel memory in exec().
// NOTE: Be extremely careful with allocating any kernel memory in this function.
// On success, the kernel stack will be lost.
auto params = TRY(copy_typed_from_user(user_params));
@ -905,9 +870,37 @@ ErrorOr<FlatPtr> Process::sys$execve(Userspace<const Syscall::SC_execve_params*>
NonnullOwnPtrVector<KString> environment;
TRY(copy_user_strings(params.environment, environment));
TRY(exec(move(path), move(arguments), move(environment)));
// We should never continue after a successful exec!
VERIFY_NOT_REACHED();
Thread* new_main_thread = nullptr;
u32 prev_flags = 0;
TRY(exec(move(path), move(arguments), move(environment), new_main_thread, prev_flags));
// NOTE: If we're here, the exec has succeeded and we've got a new executable image!
// We will not return normally from this function. Instead, the next time we
// get scheduled, it'll be at the entry point of the new executable.
VERIFY_INTERRUPTS_DISABLED();
VERIFY(Processor::in_critical());
auto* current_thread = Thread::current();
if (current_thread == new_main_thread) {
// We need to enter the scheduler lock before changing the state
// and it will be released after the context switch into that
// thread. We should also still be in our critical section
VERIFY(!g_scheduler_lock.is_locked_by_current_processor());
VERIFY(Processor::in_critical() == 1);
g_scheduler_lock.lock();
current_thread->set_state(Thread::State::Running);
Processor::assume_context(*current_thread, prev_flags);
VERIFY_NOT_REACHED();
}
// NOTE: This code path is taken in the non-syscall case, i.e when the kernel spawns
// a userspace process directly (such as /bin/SystemServer on startup)
if (prev_flags & 0x200)
sti();
Processor::leave_critical();
return 0;
}
}