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ladybird/Kernel/Syscalls/execve.cpp
Anthony Iacono f86b671de2 Kernel: Use Process::credentials() and remove user ID/group ID helpers 
Move away from using the group ID/user ID helpers in the process to
allow for us to take advantage of the immutable credentials instead.
2022-08-22 12:46:32 +02:00

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/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2022, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/ScopeGuard.h>
#include <AK/TemporaryChange.h>
#include <Kernel/Debug.h>
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/OpenFileDescription.h>
#include <Kernel/Library/LockWeakPtr.h>
#include <Kernel/Memory/AllocationStrategy.h>
#include <Kernel/Memory/MemoryManager.h>
#include <Kernel/Memory/PageDirectory.h>
#include <Kernel/Memory/Region.h>
#include <Kernel/Memory/SharedInodeVMObject.h>
#include <Kernel/Panic.h>
#include <Kernel/PerformanceManager.h>
#include <Kernel/Process.h>
#include <Kernel/Random.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Time/TimeManagement.h>
#include <LibC/limits.h>
#include <LibELF/AuxiliaryVector.h>
#include <LibELF/Image.h>
#include <LibELF/Validation.h>
namespace Kernel {
extern Memory::Region* g_signal_trampoline_region;
struct LoadResult {
OwnPtr<Memory::AddressSpace> space;
FlatPtr load_base { 0 };
FlatPtr entry_eip { 0 };
size_t size { 0 };
LockWeakPtr<Memory::Region> tls_region;
size_t tls_size { 0 };
size_t tls_alignment { 0 };
LockWeakPtr<Memory::Region> stack_region;
};
static constexpr size_t auxiliary_vector_size = 15;
static Array<ELF::AuxiliaryValue, auxiliary_vector_size> generate_auxiliary_vector(FlatPtr load_base, FlatPtr entry_eip, UserID uid, UserID euid, GroupID gid, GroupID egid, StringView executable_path, Optional<Process::ScopedDescriptionAllocation> const& main_program_fd_allocation);
static bool validate_stack_size(NonnullOwnPtrVector<KString> const& arguments, NonnullOwnPtrVector<KString>& environment)
{
size_t total_arguments_size = 0;
size_t total_environment_size = 0;
for (auto const& a : arguments)
total_arguments_size += a.length() + 1;
for (auto const& e : environment)
total_environment_size += e.length() + 1;
total_arguments_size += sizeof(char*) * (arguments.size() + 1);
total_environment_size += sizeof(char*) * (environment.size() + 1);
if (total_arguments_size > Process::max_arguments_size)
return false;
if (total_environment_size > Process::max_environment_size)
return false;
// FIXME: This doesn't account for the size of the auxiliary vector
return true;
}
static ErrorOr<FlatPtr> make_userspace_context_for_main_thread([[maybe_unused]] ThreadRegisters& regs, Memory::Region& region, NonnullOwnPtrVector<KString> const& arguments,
NonnullOwnPtrVector<KString> const& environment, Array<ELF::AuxiliaryValue, auxiliary_vector_size> auxiliary_values)
{
FlatPtr new_sp = region.range().end().get();
// Add some bits of randomness to the user stack pointer.
new_sp -= round_up_to_power_of_two(get_fast_random<u32>() % 4096, 16);
auto push_on_new_stack = [&new_sp](FlatPtr value) {
new_sp -= sizeof(FlatPtr);
Userspace<FlatPtr*> stack_ptr = new_sp;
auto result = copy_to_user(stack_ptr, &value);
VERIFY(!result.is_error());
};
auto push_aux_value_on_new_stack = [&new_sp](auxv_t value) {
new_sp -= sizeof(auxv_t);
Userspace<auxv_t*> stack_ptr = new_sp;
auto result = copy_to_user(stack_ptr, &value);
VERIFY(!result.is_error());
};
auto push_string_on_new_stack = [&new_sp](StringView string) {
new_sp -= round_up_to_power_of_two(string.length() + 1, sizeof(FlatPtr));
Userspace<FlatPtr*> stack_ptr = new_sp;
auto result = copy_to_user(stack_ptr, string.characters_without_null_termination(), string.length() + 1);
VERIFY(!result.is_error());
};
Vector<FlatPtr> argv_entries;
for (auto const& argument : arguments) {
push_string_on_new_stack(argument.view());
TRY(argv_entries.try_append(new_sp));
}
Vector<FlatPtr> env_entries;
for (auto const& variable : environment) {
push_string_on_new_stack(variable.view());
TRY(env_entries.try_append(new_sp));
}
for (auto& value : auxiliary_values) {
if (!value.optional_string.is_empty()) {
push_string_on_new_stack(value.optional_string);
value.auxv.a_un.a_ptr = (void*)new_sp;
}
if (value.auxv.a_type == ELF::AuxiliaryValue::Random) {
u8 random_bytes[16] {};
get_fast_random_bytes({ random_bytes, sizeof(random_bytes) });
push_string_on_new_stack({ random_bytes, sizeof(random_bytes) });
value.auxv.a_un.a_ptr = (void*)new_sp;
}
}
for (ssize_t i = auxiliary_values.size() - 1; i >= 0; --i) {
auto& value = auxiliary_values[i];
push_aux_value_on_new_stack(value.auxv);
}
push_on_new_stack(0);
for (ssize_t i = env_entries.size() - 1; i >= 0; --i)
push_on_new_stack(env_entries[i]);
FlatPtr envp = new_sp;
push_on_new_stack(0);
for (ssize_t i = argv_entries.size() - 1; i >= 0; --i)
push_on_new_stack(argv_entries[i]);
FlatPtr argv = new_sp;
// NOTE: The stack needs to be 16-byte aligned.
new_sp -= new_sp % 16;
#if ARCH(I386)
// GCC assumes that the return address has been pushed to the stack when it enters the function,
// so we need to reserve an extra pointer's worth of bytes below this to make GCC's stack alignment
// calculations work
new_sp -= sizeof(void*);
push_on_new_stack(envp);
push_on_new_stack(argv);
push_on_new_stack(argv_entries.size());
#elif ARCH(X86_64)
regs.rdi = argv_entries.size();
regs.rsi = argv;
regs.rdx = envp;
#else
# error Unknown architecture
#endif
VERIFY(new_sp % 16 == 0);
// FIXME: The way we're setting up the stack and passing arguments to the entry point isn't ABI-compliant
return new_sp;
}
struct RequiredLoadRange {
FlatPtr start { 0 };
FlatPtr end { 0 };
};
static ErrorOr<RequiredLoadRange> get_required_load_range(OpenFileDescription& program_description)
{
auto& inode = *(program_description.inode());
auto vmobject = TRY(Memory::SharedInodeVMObject::try_create_with_inode(inode));
size_t executable_size = inode.size();
size_t rounded_executable_size = TRY(Memory::page_round_up(executable_size));
auto region = TRY(MM.allocate_kernel_region_with_vmobject(*vmobject, rounded_executable_size, "ELF memory range calculation"sv, Memory::Region::Access::Read));
auto elf_image = ELF::Image(region->vaddr().as_ptr(), executable_size);
if (!elf_image.is_valid()) {
return EINVAL;
}
RequiredLoadRange range {};
elf_image.for_each_program_header([&range](auto const& pheader) {
if (pheader.type() != PT_LOAD)
return;
auto region_start = (FlatPtr)pheader.vaddr().as_ptr();
auto region_end = region_start + pheader.size_in_memory();
if (range.start == 0 || region_start < range.start)
range.start = region_start;
if (range.end == 0 || region_end > range.end)
range.end = region_end;
});
VERIFY(range.end > range.start);
return range;
};
static ErrorOr<FlatPtr> get_load_offset(const ElfW(Ehdr) & main_program_header, OpenFileDescription& main_program_description, OpenFileDescription* interpreter_description)
{
constexpr FlatPtr load_range_start = 0x08000000;
constexpr FlatPtr load_range_size = 65536 * PAGE_SIZE; // 2**16 * PAGE_SIZE = 256MB
constexpr FlatPtr minimum_load_offset_randomization_size = 10 * MiB;
auto random_load_offset_in_range([](auto start, auto size) {
return Memory::page_round_down(start + get_good_random<FlatPtr>() % size);
});
if (main_program_header.e_type == ET_DYN) {
return random_load_offset_in_range(load_range_start, load_range_size);
}
if (main_program_header.e_type != ET_EXEC)
return EINVAL;
auto main_program_load_range = TRY(get_required_load_range(main_program_description));
RequiredLoadRange selected_range {};
if (interpreter_description) {
auto interpreter_load_range = TRY(get_required_load_range(*interpreter_description));
auto interpreter_size_in_memory = interpreter_load_range.end - interpreter_load_range.start;
auto interpreter_load_range_end = load_range_start + load_range_size - interpreter_size_in_memory;
// No intersection
if (main_program_load_range.end < load_range_start || main_program_load_range.start > interpreter_load_range_end)
return random_load_offset_in_range(load_range_start, load_range_size);
RequiredLoadRange first_available_part = { load_range_start, main_program_load_range.start };
RequiredLoadRange second_available_part = { main_program_load_range.end, interpreter_load_range_end };
// Select larger part
if (first_available_part.end - first_available_part.start > second_available_part.end - second_available_part.start)
selected_range = first_available_part;
else
selected_range = second_available_part;
} else
selected_range = main_program_load_range;
// If main program is too big and leaves us without enough space for adequate loader randomization
if (selected_range.end - selected_range.start < minimum_load_offset_randomization_size)
return E2BIG;
return random_load_offset_in_range(selected_range.start, selected_range.end - selected_range.start);
}
enum class ShouldAllocateTls {
No,
Yes,
};
enum class ShouldAllowSyscalls {
No,
Yes,
};
static ErrorOr<LoadResult> load_elf_object(NonnullOwnPtr<Memory::AddressSpace> new_space, OpenFileDescription& object_description,
FlatPtr load_offset, ShouldAllocateTls should_allocate_tls, ShouldAllowSyscalls should_allow_syscalls)
{
auto& inode = *(object_description.inode());
auto vmobject = TRY(Memory::SharedInodeVMObject::try_create_with_inode(inode));
if (vmobject->writable_mappings()) {
dbgln("Refusing to execute a write-mapped program");
return ETXTBSY;
}
size_t executable_size = inode.size();
size_t rounded_executable_size = TRY(Memory::page_round_up(executable_size));
auto executable_region = TRY(MM.allocate_kernel_region_with_vmobject(*vmobject, rounded_executable_size, "ELF loading"sv, Memory::Region::Access::Read));
auto elf_image = ELF::Image(executable_region->vaddr().as_ptr(), executable_size);
if (!elf_image.is_valid())
return ENOEXEC;
Memory::Region* master_tls_region { nullptr };
size_t master_tls_size = 0;
size_t master_tls_alignment = 0;
FlatPtr load_base_address = 0;
auto elf_name = TRY(object_description.pseudo_path());
VERIFY(!Processor::in_critical());
Memory::MemoryManager::enter_address_space(*new_space);
auto load_tls_section = [&](auto& program_header) -> ErrorOr<void> {
VERIFY(should_allocate_tls == ShouldAllocateTls::Yes);
VERIFY(program_header.size_in_memory());
if (!elf_image.is_within_image(program_header.raw_data(), program_header.size_in_image())) {
dbgln("Shenanigans! ELF PT_TLS header sneaks outside of executable.");
return ENOEXEC;
}
auto region_name = TRY(KString::formatted("{} (master-tls)", elf_name));
master_tls_region = TRY(new_space->allocate_region(Memory::RandomizeVirtualAddress::Yes, {}, program_header.size_in_memory(), PAGE_SIZE, region_name->view(), PROT_READ | PROT_WRITE, AllocationStrategy::Reserve));
master_tls_size = program_header.size_in_memory();
master_tls_alignment = program_header.alignment();
TRY(copy_to_user(master_tls_region->vaddr().as_ptr(), program_header.raw_data(), program_header.size_in_image()));
return {};
};
auto load_writable_section = [&](auto& program_header) -> ErrorOr<void> {
// Writable section: create a copy in memory.
VERIFY(program_header.alignment() % PAGE_SIZE == 0);
if (!elf_image.is_within_image(program_header.raw_data(), program_header.size_in_image())) {
dbgln("Shenanigans! Writable ELF PT_LOAD header sneaks outside of executable.");
return ENOEXEC;
}
int prot = 0;
if (program_header.is_readable())
prot |= PROT_READ;
if (program_header.is_writable())
prot |= PROT_WRITE;
auto region_name = TRY(KString::formatted("{} (data-{}{})", elf_name, program_header.is_readable() ? "r" : "", program_header.is_writable() ? "w" : ""));
auto range_base = VirtualAddress { Memory::page_round_down(program_header.vaddr().offset(load_offset).get()) };
size_t rounded_range_end = TRY(Memory::page_round_up(program_header.vaddr().offset(load_offset).offset(program_header.size_in_memory()).get()));
auto range_end = VirtualAddress { rounded_range_end };
auto region = TRY(new_space->allocate_region(Memory::RandomizeVirtualAddress::Yes, range_base, range_end.get() - range_base.get(), PAGE_SIZE, region_name->view(), prot, AllocationStrategy::Reserve));
// It's not always the case with PIE executables (and very well shouldn't be) that the
// virtual address in the program header matches the one we end up giving the process.
// In order to copy the data image correctly into memory, we need to copy the data starting at
// the right initial page offset into the pages allocated for the elf_alloc-XX section.
// FIXME: There's an opportunity to munmap, or at least mprotect, the padding space between
// the .text and .data PT_LOAD sections of the executable.
// Accessing it would definitely be a bug.
auto page_offset = program_header.vaddr();
page_offset.mask(~PAGE_MASK);
TRY(copy_to_user((u8*)region->vaddr().as_ptr() + page_offset.get(), program_header.raw_data(), program_header.size_in_image()));
return {};
};
auto load_section = [&](auto& program_header) -> ErrorOr<void> {
if (program_header.size_in_memory() == 0)
return {};
if (program_header.is_writable())
return load_writable_section(program_header);
// Non-writable section: map the executable itself in memory.
VERIFY(program_header.alignment() % PAGE_SIZE == 0);
int prot = 0;
if (program_header.is_readable())
prot |= PROT_READ;
if (program_header.is_writable())
prot |= PROT_WRITE;
if (program_header.is_executable())
prot |= PROT_EXEC;
auto range_base = VirtualAddress { Memory::page_round_down(program_header.vaddr().offset(load_offset).get()) };
size_t rounded_range_end = TRY(Memory::page_round_up(program_header.vaddr().offset(load_offset).offset(program_header.size_in_memory()).get()));
auto range_end = VirtualAddress { rounded_range_end };
auto region = TRY(new_space->allocate_region_with_vmobject(Memory::RandomizeVirtualAddress::Yes, range_base, range_end.get() - range_base.get(), program_header.alignment(), *vmobject, program_header.offset(), elf_name->view(), prot, true));
if (should_allow_syscalls == ShouldAllowSyscalls::Yes)
region->set_syscall_region(true);
if (program_header.offset() == 0)
load_base_address = (FlatPtr)region->vaddr().as_ptr();
return {};
};
auto load_elf_program_header = [&](auto& program_header) -> ErrorOr<void> {
if (program_header.type() == PT_TLS)
return load_tls_section(program_header);
if (program_header.type() == PT_LOAD)
return load_section(program_header);
// NOTE: We ignore other program header types.
return {};
};
TRY([&] {
ErrorOr<void> result;
elf_image.for_each_program_header([&](ELF::Image::ProgramHeader const& program_header) {
result = load_elf_program_header(program_header);
return result.is_error() ? IterationDecision::Break : IterationDecision::Continue;
});
return result;
}());
if (!elf_image.entry().offset(load_offset).get()) {
dbgln("do_exec: Failure loading program, entry pointer is invalid! {})", elf_image.entry().offset(load_offset));
return ENOEXEC;
}
auto* stack_region = TRY(new_space->allocate_region(Memory::RandomizeVirtualAddress::Yes, {}, Thread::default_userspace_stack_size, PAGE_SIZE, "Stack (Main thread)"sv, PROT_READ | PROT_WRITE, AllocationStrategy::Reserve));
stack_region->set_stack(true);
return LoadResult {
move(new_space),
load_base_address,
elf_image.entry().offset(load_offset).get(),
executable_size,
TRY(AK::try_make_weak_ptr_if_nonnull(master_tls_region)),
master_tls_size,
master_tls_alignment,
TRY(stack_region->try_make_weak_ptr())
};
}
ErrorOr<LoadResult>
Process::load(NonnullLockRefPtr<OpenFileDescription> main_program_description,
LockRefPtr<OpenFileDescription> interpreter_description, const ElfW(Ehdr) & main_program_header)
{
auto new_space = TRY(Memory::AddressSpace::try_create(nullptr));
ScopeGuard space_guard([&]() {
Memory::MemoryManager::enter_process_address_space(*this);
});
auto load_offset = TRY(get_load_offset(main_program_header, main_program_description, interpreter_description));
if (interpreter_description.is_null()) {
auto load_result = TRY(load_elf_object(move(new_space), main_program_description, load_offset, ShouldAllocateTls::Yes, ShouldAllowSyscalls::No));
m_master_tls_region = load_result.tls_region;
m_master_tls_size = load_result.tls_size;
m_master_tls_alignment = load_result.tls_alignment;
return load_result;
}
auto interpreter_load_result = TRY(load_elf_object(move(new_space), *interpreter_description, load_offset, ShouldAllocateTls::No, ShouldAllowSyscalls::Yes));
// TLS allocation will be done in userspace by the loader
VERIFY(!interpreter_load_result.tls_region);
VERIFY(!interpreter_load_result.tls_alignment);
VERIFY(!interpreter_load_result.tls_size);
return interpreter_load_result;
}
void Process::clear_signal_handlers_for_exec()
{
// Comments are as they are presented in the POSIX specification, but slightly out of order.
for (size_t signal = 0; signal < m_signal_action_data.size(); signal++) {
// Except for SIGCHLD, signals set to be ignored by the calling process image shall be set to be ignored by the new process image.
// If the SIGCHLD signal is set to be ignored by the calling process image, it is unspecified whether the SIGCHLD signal is set
// to be ignored or to the default action in the new process image.
if (signal != SIGCHLD && m_signal_action_data[signal].handler_or_sigaction.get() == reinterpret_cast<FlatPtr>(SIG_IGN)) {
m_signal_action_data[signal] = {};
m_signal_action_data[signal].handler_or_sigaction.set(reinterpret_cast<FlatPtr>(SIG_IGN));
continue;
}
// Signals set to the default action in the calling process image shall be set to the default action in the new process image.
// Signals set to be caught by the calling process image shall be set to the default action in the new process image.
m_signal_action_data[signal] = {};
}
}
ErrorOr<void> Process::do_exec(NonnullLockRefPtr<OpenFileDescription> main_program_description, NonnullOwnPtrVector<KString> arguments, NonnullOwnPtrVector<KString> environment,
LockRefPtr<OpenFileDescription> interpreter_description, Thread*& new_main_thread, u32& prev_flags, const ElfW(Ehdr) & main_program_header)
{
VERIFY(is_user_process());
VERIFY(!Processor::in_critical());
// Although we *could* handle a pseudo_path here, trying to execute something that doesn't have
// a custody (e.g. BlockDevice or RandomDevice) is pretty suspicious anyway.
auto path = TRY(main_program_description->original_absolute_path());
dbgln_if(EXEC_DEBUG, "do_exec: {}", path);
// FIXME: How much stack space does process startup need?
if (!validate_stack_size(arguments, environment))
return E2BIG;
auto last_part = path->view().find_last_split_view('/');
auto new_process_name = TRY(KString::try_create(last_part));
auto new_main_thread_name = TRY(new_process_name->try_clone());
auto load_result = TRY(load(main_program_description, interpreter_description, main_program_header));
// NOTE: We don't need the interpreter executable description after this point.
// We destroy it here to prevent it from getting destroyed when we return from this function.
// That's important because when we're returning from this function, we're in a very delicate
// state where we can't block (e.g by trying to acquire a mutex in description teardown.)
bool has_interpreter = interpreter_description;
interpreter_description = nullptr;
auto* signal_trampoline_region = TRY(load_result.space->allocate_region_with_vmobject(Memory::RandomizeVirtualAddress::Yes, {}, PAGE_SIZE, PAGE_SIZE, g_signal_trampoline_region->vmobject(), 0, "Signal trampoline"sv, PROT_READ | PROT_EXEC, true));
signal_trampoline_region->set_syscall_region(true);
// (For dynamically linked executable) Allocate an FD for passing the main executable to the dynamic loader.
Optional<ScopedDescriptionAllocation> main_program_fd_allocation;
if (has_interpreter)
main_program_fd_allocation = TRY(allocate_fd());
auto old_credentials = this->credentials();
auto new_credentials = old_credentials;
bool executable_is_setid = false;
if (!(main_program_description->custody()->mount_flags() & MS_NOSUID)) {
auto main_program_metadata = main_program_description->metadata();
auto new_euid = old_credentials->euid();
auto new_egid = old_credentials->egid();
auto new_suid = old_credentials->suid();
auto new_sgid = old_credentials->sgid();
if (main_program_metadata.is_setuid()) {
executable_is_setid = true;
new_euid = main_program_metadata.uid;
new_suid = main_program_metadata.uid;
}
if (main_program_metadata.is_setgid()) {
executable_is_setid = true;
new_egid = main_program_metadata.gid;
new_sgid = main_program_metadata.gid;
}
if (executable_is_setid) {
new_credentials = TRY(Credentials::create(
old_credentials->uid(),
old_credentials->gid(),
new_euid,
new_egid,
new_suid,
new_sgid,
old_credentials->extra_gids()));
}
}
// We commit to the new executable at this point. There is no turning back!
// Prevent other processes from attaching to us with ptrace while we're doing this.
MutexLocker ptrace_locker(ptrace_lock());
// Disable profiling temporarily in case it's running on this process.
auto was_profiling = m_profiling;
TemporaryChange profiling_disabler(m_profiling, false);
kill_threads_except_self();
with_mutable_protected_data([&](auto& protected_data) {
protected_data.credentials = move(new_credentials);
protected_data.dumpable = !executable_is_setid;
});
// We make sure to enter the new address space before destroying the old one.
// This ensures that the process always has a valid page directory.
Memory::MemoryManager::enter_address_space(*load_result.space);
m_space = load_result.space.release_nonnull();
m_executable.with([&](auto& executable) { executable = main_program_description->custody(); });
m_arguments = move(arguments);
m_environment = move(environment);
TRY(m_unveil_data.with([&](auto& unveil_data) -> ErrorOr<void> {
unveil_data.state = VeilState::None;
unveil_data.paths.clear();
unveil_data.paths.set_metadata({ TRY(KString::try_create("/"sv)), UnveilAccess::None, false });
return {};
}));
m_coredump_properties.for_each([](auto& property) {
property = {};
});
auto* current_thread = Thread::current();
current_thread->reset_signals_for_exec();
clear_signal_handlers_for_exec();
clear_futex_queues_on_exec();
m_fds.with_exclusive([&](auto& fds) {
fds.change_each([&](auto& file_description_metadata) {
if (file_description_metadata.is_valid() && file_description_metadata.flags() & FD_CLOEXEC)
file_description_metadata = {};
});
});
if (main_program_fd_allocation.has_value()) {
main_program_description->set_readable(true);
m_fds.with_exclusive([&](auto& fds) { fds[main_program_fd_allocation->fd].set(move(main_program_description), FD_CLOEXEC); });
}
new_main_thread = nullptr;
if (&current_thread->process() == this) {
new_main_thread = current_thread;
} else {
for_each_thread([&](auto& thread) {
new_main_thread = &thread;
return IterationDecision::Break;
});
}
VERIFY(new_main_thread);
auto credentials = this->credentials();
auto auxv = generate_auxiliary_vector(load_result.load_base, load_result.entry_eip, credentials->uid(), credentials->euid(), credentials->gid(), credentials->egid(), path->view(), main_program_fd_allocation);
// NOTE: We create the new stack before disabling interrupts since it will zero-fault
// and we don't want to deal with faults after this point.
auto new_userspace_sp = TRY(make_userspace_context_for_main_thread(new_main_thread->regs(), *load_result.stack_region.unsafe_ptr(), m_arguments, m_environment, move(auxv)));
m_name = move(new_process_name);
new_main_thread->set_name(move(new_main_thread_name));
if (wait_for_tracer_at_next_execve()) {
// Make sure we release the ptrace lock here or the tracer will block forever.
ptrace_locker.unlock();
Thread::current()->send_urgent_signal_to_self(SIGSTOP);
} else {
// Unlock regardless before disabling interrupts.
// Ensure we always unlock after checking ptrace status to avoid TOCTOU ptrace issues
ptrace_locker.unlock();
}
// We enter a critical section here because we don't want to get interrupted between do_exec()
// and Processor::assume_context() or the next context switch.
// If we used an InterruptDisabler that sti()'d on exit, we might timer tick'd too soon in exec().
Processor::enter_critical();
prev_flags = cpu_flags();
cli();
// NOTE: Be careful to not trigger any page faults below!
with_mutable_protected_data([&](auto& protected_data) {
protected_data.promises = protected_data.execpromises.load();
protected_data.has_promises = protected_data.has_execpromises.load();
protected_data.execpromises = 0;
protected_data.has_execpromises = false;
protected_data.signal_trampoline = signal_trampoline_region->vaddr();
// FIXME: PID/TID ISSUE
protected_data.pid = new_main_thread->tid().value();
});
auto tsr_result = new_main_thread->make_thread_specific_region({});
if (tsr_result.is_error()) {
// FIXME: We cannot fail this late. Refactor this so the allocation happens before we commit to the new executable.
VERIFY_NOT_REACHED();
}
new_main_thread->reset_fpu_state();
auto& regs = new_main_thread->m_regs;
regs.cs = GDT_SELECTOR_CODE3 | 3;
#if ARCH(I386)
regs.ds = GDT_SELECTOR_DATA3 | 3;
regs.es = GDT_SELECTOR_DATA3 | 3;
regs.ss = GDT_SELECTOR_DATA3 | 3;
regs.fs = GDT_SELECTOR_DATA3 | 3;
regs.gs = GDT_SELECTOR_TLS | 3;
regs.eip = load_result.entry_eip;
regs.esp = new_userspace_sp;
#else
regs.rip = load_result.entry_eip;
regs.rsp = new_userspace_sp;
#endif
regs.cr3 = address_space().page_directory().cr3();
{
TemporaryChange profiling_disabler(m_profiling, was_profiling);
PerformanceManager::add_process_exec_event(*this);
}
u32 lock_count_to_restore;
[[maybe_unused]] auto rc = big_lock().force_unlock_exclusive_if_locked(lock_count_to_restore);
VERIFY_INTERRUPTS_DISABLED();
VERIFY(Processor::in_critical());
return {};
}
static Array<ELF::AuxiliaryValue, auxiliary_vector_size> generate_auxiliary_vector(FlatPtr load_base, FlatPtr entry_eip, UserID uid, UserID euid, GroupID gid, GroupID egid, StringView executable_path, Optional<Process::ScopedDescriptionAllocation> const& main_program_fd_allocation)
{
return { {
// PHDR/EXECFD
// PH*
{ ELF::AuxiliaryValue::PageSize, PAGE_SIZE },
{ ELF::AuxiliaryValue::BaseAddress, (void*)load_base },
{ ELF::AuxiliaryValue::Entry, (void*)entry_eip },
// NOTELF
{ ELF::AuxiliaryValue::Uid, (long)uid.value() },
{ ELF::AuxiliaryValue::EUid, (long)euid.value() },
{ ELF::AuxiliaryValue::Gid, (long)gid.value() },
{ ELF::AuxiliaryValue::EGid, (long)egid.value() },
{ ELF::AuxiliaryValue::Platform, Processor::platform_string() },
// FIXME: This is platform specific
{ ELF::AuxiliaryValue::HwCap, (long)CPUID(1).edx() },
{ ELF::AuxiliaryValue::ClockTick, (long)TimeManagement::the().ticks_per_second() },
// FIXME: Also take into account things like extended filesystem permissions? That's what linux does...
{ ELF::AuxiliaryValue::Secure, ((uid != euid) || (gid != egid)) ? 1 : 0 },
{ ELF::AuxiliaryValue::Random, nullptr },
{ ELF::AuxiliaryValue::ExecFilename, executable_path },
main_program_fd_allocation.has_value() ? ELF::AuxiliaryValue { ELF::AuxiliaryValue::ExecFileDescriptor, main_program_fd_allocation->fd } : ELF::AuxiliaryValue { ELF::AuxiliaryValue::Ignore, 0L },
{ ELF::AuxiliaryValue::Null, 0L },
} };
}
static ErrorOr<NonnullOwnPtrVector<KString>> find_shebang_interpreter_for_executable(char const first_page[], size_t nread)
{
int word_start = 2;
size_t word_length = 0;
if (nread > 2 && first_page[0] == '#' && first_page[1] == '!') {
NonnullOwnPtrVector<KString> interpreter_words;
for (size_t i = 2; i < nread; ++i) {
if (first_page[i] == '\n') {
break;
}
if (first_page[i] != ' ') {
++word_length;
}
if (first_page[i] == ' ') {
if (word_length > 0) {
auto word = TRY(KString::try_create(StringView { &first_page[word_start], word_length }));
TRY(interpreter_words.try_append(move(word)));
}
word_length = 0;
word_start = i + 1;
}
}
if (word_length > 0) {
auto word = TRY(KString::try_create(StringView { &first_page[word_start], word_length }));
TRY(interpreter_words.try_append(move(word)));
}
if (!interpreter_words.is_empty())
return interpreter_words;
}
return ENOEXEC;
}
ErrorOr<LockRefPtr<OpenFileDescription>> Process::find_elf_interpreter_for_executable(StringView path, ElfW(Ehdr) const& main_executable_header, size_t main_executable_header_size, size_t file_size)
{
// Not using ErrorOr here because we'll want to do the same thing in userspace in the RTLD
StringBuilder interpreter_path_builder;
if (!TRY(ELF::validate_program_headers(main_executable_header, file_size, { &main_executable_header, main_executable_header_size }, &interpreter_path_builder))) {
dbgln("exec({}): File has invalid ELF Program headers", path);
return ENOEXEC;
}
auto interpreter_path = interpreter_path_builder.string_view();
if (!interpreter_path.is_empty()) {
dbgln_if(EXEC_DEBUG, "exec({}): Using program interpreter {}", path, interpreter_path);
auto interpreter_description = TRY(VirtualFileSystem::the().open(credentials(), interpreter_path, O_EXEC, 0, current_directory()));
auto interp_metadata = interpreter_description->metadata();
VERIFY(interpreter_description->inode());
// Validate the program interpreter as a valid elf binary.
// If your program interpreter is a #! file or something, it's time to stop playing games :)
if (interp_metadata.size < (int)sizeof(ElfW(Ehdr)))
return ENOEXEC;
char first_page[PAGE_SIZE] = {};
auto first_page_buffer = UserOrKernelBuffer::for_kernel_buffer((u8*)&first_page);
auto nread = TRY(interpreter_description->read(first_page_buffer, sizeof(first_page)));
if (nread < sizeof(ElfW(Ehdr)))
return ENOEXEC;
auto* elf_header = (ElfW(Ehdr)*)first_page;
if (!ELF::validate_elf_header(*elf_header, interp_metadata.size)) {
dbgln("exec({}): Interpreter ({}) has invalid ELF header", path, interpreter_path);
return ENOEXEC;
}
// Not using ErrorOr here because we'll want to do the same thing in userspace in the RTLD
StringBuilder interpreter_interpreter_path_builder;
if (!TRY(ELF::validate_program_headers(*elf_header, interp_metadata.size, { first_page, nread }, &interpreter_interpreter_path_builder))) {
dbgln("exec({}): Interpreter ({}) has invalid ELF Program headers", path, interpreter_path);
return ENOEXEC;
}
auto interpreter_interpreter_path = interpreter_interpreter_path_builder.string_view();
if (!interpreter_interpreter_path.is_empty()) {
dbgln("exec({}): Interpreter ({}) has its own interpreter ({})! No thank you!", path, interpreter_path, interpreter_interpreter_path);
return ELOOP;
}
return interpreter_description;
}
if (main_executable_header.e_type == ET_REL) {
// We can't exec an ET_REL, that's just an object file from the compiler
return ENOEXEC;
}
if (main_executable_header.e_type == ET_DYN) {
// If it's ET_DYN with no PT_INTERP, then it's a dynamic executable responsible
// for its own relocation (i.e. it's /usr/lib/Loader.so)
if (path != "/usr/lib/Loader.so")
dbgln("exec({}): WARNING - Dynamic ELF executable without a PT_INTERP header, and isn't /usr/lib/Loader.so", path);
return nullptr;
}
// No interpreter, but, path refers to a valid elf image
return nullptr;
}
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);
return ELOOP;
}
// Open the file to check what kind of binary format it is
// Currently supported formats:
// - #! interpreted file
// - ELF32
// * ET_EXEC binary that just gets loaded
// * ET_DYN binary that requires a program interpreter
//
auto description = TRY(VirtualFileSystem::the().open(credentials(), path->view(), O_EXEC, 0, current_directory()));
auto metadata = description->metadata();
if (!metadata.is_regular_file())
return EACCES;
// Always gonna need at least 3 bytes. these are for #!X
if (metadata.size < 3)
return ENOEXEC;
VERIFY(description->inode());
// Read the first page of the program into memory so we can validate the binfmt of it
char first_page[PAGE_SIZE];
auto first_page_buffer = UserOrKernelBuffer::for_kernel_buffer((u8*)&first_page);
auto nread = TRY(description->read(first_page_buffer, sizeof(first_page)));
// 1) #! interpreted file
auto shebang_result = find_shebang_interpreter_for_executable(first_page, nread);
if (!shebang_result.is_error()) {
auto shebang_words = shebang_result.release_value();
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), new_main_thread, prev_flags, ++recursion_depth);
}
// #2) ELF32 for i386
if (nread < sizeof(ElfW(Ehdr)))
return ENOEXEC;
auto const* main_program_header = (ElfW(Ehdr)*)first_page;
if (!ELF::validate_elf_header(*main_program_header, metadata.size)) {
dbgln("exec({}): File has invalid ELF header", path);
return ENOEXEC;
}
auto interpreter_description = TRY(find_elf_interpreter_for_executable(path->view(), *main_program_header, nread, metadata.size));
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<Syscall::SC_execve_params const*> user_params)
{
VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
TRY(require_promise(Pledge::exec));
Thread* new_main_thread = nullptr;
u32 prev_flags = 0;
// NOTE: Be extremely careful with allocating any kernel memory in this function.
// On success, the kernel stack will be lost.
// The explicit block scope below is specifically placed to minimize the number
// of stack locals in this function.
{
auto params = TRY(copy_typed_from_user(user_params));
if (params.arguments.length > ARG_MAX || params.environment.length > ARG_MAX)
return E2BIG;
// NOTE: The caller is expected to always pass at least one argument by convention,
// the program path that was passed as params.path.
if (params.arguments.length == 0)
return EINVAL;
auto path = TRY(get_syscall_path_argument(params.path));
auto copy_user_strings = [](auto const& list, auto& output) -> ErrorOr<void> {
if (!list.length)
return {};
Checked<size_t> size = sizeof(*list.strings);
size *= list.length;
if (size.has_overflow())
return EOVERFLOW;
Vector<Syscall::StringArgument, 32> strings;
TRY(strings.try_resize(list.length));
TRY(copy_from_user(strings.data(), list.strings, size.value()));
for (size_t i = 0; i < list.length; ++i) {
auto string = TRY(try_copy_kstring_from_user(strings[i]));
TRY(output.try_append(move(string)));
}
return {};
};
NonnullOwnPtrVector<KString> arguments;
TRY(copy_user_strings(params.arguments, arguments));
NonnullOwnPtrVector<KString> environment;
TRY(copy_user_strings(params.environment, environment));
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;
}
}
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