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serenity/Kernel/Syscalls/execve.cpp
Liav A 01b79910b3 Kernel/Process: Move protected values to the end of the object 
The compiler can re-order the structure (class) members if that's
necessary, so if we make Process to inherit from ProcFSExposedComponent,
even if the declaration is to inherit first from ProcessBase, then from
ProcFSExposedComponent and last from Weakable<Process>, the members of
class ProcFSExposedComponent (including the Ref-counted parts) are the
first members of the Process class.

This problem made it impossible to safely use the current toggling
method with the write-protection bit on the ProcessBase members, so
instead of inheriting from it, we make its members the last ones in the
Process class so we can safely locate and modify the corresponding page
write protection bit of these values.

We make sure that the Process class doesn't expand beyond 8192 bytes and
the protected values are always aligned on a page boundary.
2021-08-12 20:57:32 +02:00

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/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/ScopeGuard.h>
#include <AK/TemporaryChange.h>
#include <AK/WeakPtr.h>
#include <Kernel/Debug.h>
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/FileDescription.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/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 };
WeakPtr<Memory::Region> tls_region;
size_t tls_size { 0 };
size_t tls_alignment { 0 };
WeakPtr<Memory::Region> stack_region;
};
static Vector<ELF::AuxiliaryValue> generate_auxiliary_vector(FlatPtr load_base, FlatPtr entry_eip, uid_t uid, uid_t euid, gid_t gid, gid_t egid, String executable_path, int main_program_fd);
static bool validate_stack_size(const Vector<String>& arguments, const Vector<String>& environment)
{
size_t total_arguments_size = 0;
size_t total_environment_size = 0;
for (auto& a : arguments)
total_arguments_size += a.length() + 1;
for (auto& e : environment)
total_environment_size += e.length() + 1;
total_arguments_size += sizeof(char*) * (arguments.size() + 1);
total_environment_size += sizeof(char*) * (environment.size() + 1);
static constexpr size_t max_arguments_size = Thread::default_userspace_stack_size / 8;
static constexpr size_t max_environment_size = Thread::default_userspace_stack_size / 8;
if (total_arguments_size > max_arguments_size)
return false;
if (total_environment_size > max_environment_size)
return false;
// FIXME: This doesn't account for the size of the auxiliary vector
return true;
}
static KResultOr<FlatPtr> make_userspace_context_for_main_thread([[maybe_unused]] ThreadRegisters& regs, Memory::Region& region, Vector<String> arguments,
Vector<String> environment, Vector<ELF::AuxiliaryValue> 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;
return copy_to_user(stack_ptr, &value);
};
auto push_aux_value_on_new_stack = [&new_sp](auxv_t value) {
new_sp -= sizeof(auxv_t);
Userspace<auxv_t*> stack_ptr = new_sp;
return copy_to_user(stack_ptr, &value);
};
auto push_string_on_new_stack = [&new_sp](const String& string) {
new_sp -= round_up_to_power_of_two(string.length() + 1, sizeof(FlatPtr));
Userspace<FlatPtr*> stack_ptr = new_sp;
return copy_to_user(stack_ptr, string.characters(), string.length() + 1);
};
Vector<FlatPtr> argv_entries;
for (auto& argument : arguments) {
push_string_on_new_stack(argument);
if (!argv_entries.try_append(new_sp))
return ENOMEM;
}
Vector<FlatPtr> env_entries;
for (auto& variable : environment) {
push_string_on_new_stack(variable);
if (!env_entries.try_append(new_sp))
return ENOMEM;
}
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;
}
}
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());
#else
regs.rdi = argv_entries.size();
regs.rsi = argv;
regs.rdx = envp;
#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 KResultOr<RequiredLoadRange> get_required_load_range(FileDescription& program_description)
{
auto& inode = *(program_description.inode());
auto vmobject = Memory::SharedInodeVMObject::try_create_with_inode(inode);
if (!vmobject) {
dbgln("get_required_load_range: Unable to allocate SharedInodeVMObject");
return ENOMEM;
}
size_t executable_size = inode.size();
auto region = MM.allocate_kernel_region_with_vmobject(*vmobject, Memory::page_round_up(executable_size), "ELF memory range calculation", Memory::Region::Access::Read);
if (!region) {
dbgln("Could not allocate memory for ELF");
return ENOMEM;
}
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](const auto& 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 KResultOr<FlatPtr> get_load_offset(const ElfW(Ehdr) & main_program_header, FileDescription& main_program_description, FileDescription* 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_result = get_required_load_range(main_program_description);
if (main_program_load_range_result.is_error())
return main_program_load_range_result.error();
auto main_program_load_range = main_program_load_range_result.value();
RequiredLoadRange selected_range {};
if (interpreter_description) {
auto interpreter_load_range_result = get_required_load_range(*interpreter_description);
if (interpreter_load_range_result.is_error())
return interpreter_load_range_result.error();
auto interpreter_size_in_memory = interpreter_load_range_result.value().end - interpreter_load_range_result.value().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 KResultOr<LoadResult> load_elf_object(NonnullOwnPtr<Memory::AddressSpace> new_space, FileDescription& object_description,
FlatPtr load_offset, ShouldAllocateTls should_allocate_tls, ShouldAllowSyscalls should_allow_syscalls)
{
auto& inode = *(object_description.inode());
auto vmobject = Memory::SharedInodeVMObject::try_create_with_inode(inode);
if (!vmobject) {
dbgln("load_elf_object: Unable to allocate SharedInodeVMObject");
return ENOMEM;
}
if (vmobject->writable_mappings()) {
dbgln("Refusing to execute a write-mapped program");
return ETXTBSY;
}
size_t executable_size = inode.size();
auto executable_region = MM.allocate_kernel_region_with_vmobject(*vmobject, Memory::page_round_up(executable_size), "ELF loading", Memory::Region::Access::Read);
if (!executable_region) {
dbgln("Could not allocate memory for ELF loading");
return ENOMEM;
}
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;
String elf_name = object_description.absolute_path();
VERIFY(!Processor::in_critical());
Memory::MemoryManager::enter_space(*new_space);
KResult ph_load_result = KSuccess;
elf_image.for_each_program_header([&](const ELF::Image::ProgramHeader& program_header) {
if (program_header.type() == PT_TLS) {
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.");
ph_load_result = ENOEXEC;
return IterationDecision::Break;
}
auto range = new_space->allocate_range({}, program_header.size_in_memory());
if (!range.has_value()) {
ph_load_result = ENOMEM;
return IterationDecision::Break;
}
auto region_or_error = new_space->allocate_region(range.value(), String::formatted("{} (master-tls)", elf_name), PROT_READ | PROT_WRITE, AllocationStrategy::Reserve);
if (region_or_error.is_error()) {
ph_load_result = region_or_error.error();
return IterationDecision::Break;
}
master_tls_region = region_or_error.value();
master_tls_size = program_header.size_in_memory();
master_tls_alignment = program_header.alignment();
if (!copy_to_user(master_tls_region->vaddr().as_ptr(), program_header.raw_data(), program_header.size_in_image())) {
ph_load_result = EFAULT;
return IterationDecision::Break;
}
return IterationDecision::Continue;
}
if (program_header.type() != PT_LOAD)
return IterationDecision::Continue;
if (program_header.is_writable()) {
// Writable section: create a copy in memory.
VERIFY(program_header.size_in_memory());
VERIFY(program_header.alignment() == PAGE_SIZE);
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.");
ph_load_result = ENOEXEC;
return IterationDecision::Break;
}
int prot = 0;
if (program_header.is_readable())
prot |= PROT_READ;
if (program_header.is_writable())
prot |= PROT_WRITE;
auto region_name = String::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()) };
auto range_end = VirtualAddress { Memory::page_round_up(program_header.vaddr().offset(load_offset).offset(program_header.size_in_memory()).get()) };
auto range = new_space->allocate_range(range_base, range_end.get() - range_base.get());
if (!range.has_value()) {
ph_load_result = ENOMEM;
return IterationDecision::Break;
}
auto region_or_error = new_space->allocate_region(range.value(), region_name, prot, AllocationStrategy::Reserve);
if (region_or_error.is_error()) {
ph_load_result = region_or_error.error();
return IterationDecision::Break;
}
// 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);
if (!copy_to_user((u8*)region_or_error.value()->vaddr().as_ptr() + page_offset.get(), program_header.raw_data(), program_header.size_in_image())) {
ph_load_result = EFAULT;
return IterationDecision::Break;
}
return IterationDecision::Continue;
}
// Non-writable section: map the executable itself in memory.
VERIFY(program_header.size_in_memory());
VERIFY(program_header.alignment() == PAGE_SIZE);
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()) };
auto range_end = VirtualAddress { Memory::page_round_up(program_header.vaddr().offset(load_offset).offset(program_header.size_in_memory()).get()) };
auto range = new_space->allocate_range(range_base, range_end.get() - range_base.get());
if (!range.has_value()) {
ph_load_result = ENOMEM;
return IterationDecision::Break;
}
auto region_or_error = new_space->allocate_region_with_vmobject(range.value(), *vmobject, program_header.offset(), elf_name, prot, true);
if (region_or_error.is_error()) {
ph_load_result = region_or_error.error();
return IterationDecision::Break;
}
if (should_allow_syscalls == ShouldAllowSyscalls::Yes)
region_or_error.value()->set_syscall_region(true);
if (program_header.offset() == 0)
load_base_address = (FlatPtr)region_or_error.value()->vaddr().as_ptr();
return IterationDecision::Continue;
});
if (ph_load_result.is_error()) {
dbgln("do_exec: Failure loading program ({})", ph_load_result.error());
return ph_load_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_range = new_space->allocate_range({}, Thread::default_userspace_stack_size);
if (!stack_range.has_value()) {
dbgln("do_exec: Failed to allocate VM range for stack");
return ENOMEM;
}
auto stack_region_or_error = new_space->allocate_region(stack_range.value(), "Stack (Main thread)", PROT_READ | PROT_WRITE, AllocationStrategy::Reserve);
if (stack_region_or_error.is_error())
return stack_region_or_error.error();
auto& stack_region = *stack_region_or_error.value();
stack_region.set_stack(true);
return LoadResult {
move(new_space),
load_base_address,
elf_image.entry().offset(load_offset).get(),
executable_size,
AK::try_make_weak_ptr(master_tls_region),
master_tls_size,
master_tls_alignment,
stack_region.make_weak_ptr()
};
}
KResultOr<LoadResult> Process::load(NonnullRefPtr<FileDescription> main_program_description,
RefPtr<FileDescription> interpreter_description, const ElfW(Ehdr) & main_program_header)
{
auto new_space = Memory::AddressSpace::try_create(nullptr);
if (!new_space)
return ENOMEM;
ScopeGuard space_guard([&]() {
Memory::MemoryManager::enter_process_paging_scope(*this);
});
auto load_offset = get_load_offset(main_program_header, main_program_description, interpreter_description);
if (load_offset.is_error()) {
return load_offset.error();
}
if (interpreter_description.is_null()) {
auto result = load_elf_object(new_space.release_nonnull(), main_program_description, load_offset.value(), ShouldAllocateTls::Yes, ShouldAllowSyscalls::No);
if (result.is_error())
return result.error();
m_master_tls_region = result.value().tls_region;
m_master_tls_size = result.value().tls_size;
m_master_tls_alignment = result.value().tls_alignment;
return result;
}
auto interpreter_load_result = load_elf_object(new_space.release_nonnull(), *interpreter_description, load_offset.value(), ShouldAllocateTls::No, ShouldAllowSyscalls::Yes);
if (interpreter_load_result.is_error())
return interpreter_load_result.error();
// TLS allocation will be done in userspace by the loader
VERIFY(!interpreter_load_result.value().tls_region);
VERIFY(!interpreter_load_result.value().tls_alignment);
VERIFY(!interpreter_load_result.value().tls_size);
return interpreter_load_result;
}
KResult Process::do_exec(NonnullRefPtr<FileDescription> main_program_description, Vector<String> arguments, Vector<String> environment,
RefPtr<FileDescription> interpreter_description, Thread*& new_main_thread, u32& prev_flags, const ElfW(Ehdr) & main_program_header)
{
VERIFY(is_user_process());
VERIFY(!Processor::in_critical());
auto path = main_program_description->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 parts = path.split('/');
if (parts.is_empty())
return ENOENT;
auto main_program_metadata = main_program_description->metadata();
auto load_result_or_error = load(main_program_description, interpreter_description, main_program_header);
if (load_result_or_error.is_error()) {
dbgln("do_exec: Failed to load main program or interpreter for {}", path);
return load_result_or_error.error();
}
auto signal_trampoline_range = load_result_or_error.value().space->allocate_range({}, PAGE_SIZE);
if (!signal_trampoline_range.has_value()) {
dbgln("do_exec: Failed to allocate VM for signal trampoline");
return ENOMEM;
}
// 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();
auto& load_result = load_result_or_error.value();
bool executable_is_setid = false;
if (!(main_program_description->custody()->mount_flags() & MS_NOSUID)) {
if (main_program_metadata.is_setuid()) {
executable_is_setid = true;
ProtectedDataMutationScope scope { *this };
m_protected_values.euid = main_program_metadata.uid;
m_protected_values.suid = main_program_metadata.uid;
}
if (main_program_metadata.is_setgid()) {
executable_is_setid = true;
ProtectedDataMutationScope scope { *this };
m_protected_values.egid = main_program_metadata.gid;
m_protected_values.sgid = main_program_metadata.gid;
}
}
set_dumpable(!executable_is_setid);
{
// We must disable global profiling (especially kfree tracing) here because
// we might otherwise end up walking the stack into the process' space that
// is about to be destroyed.
TemporaryChange global_profiling_disabler(g_profiling_all_threads, false);
m_space = load_result.space.release_nonnull();
}
Memory::MemoryManager::enter_space(*m_space);
auto signal_trampoline_region = m_space->allocate_region_with_vmobject(signal_trampoline_range.value(), g_signal_trampoline_region->vmobject(), 0, "Signal trampoline", PROT_READ | PROT_EXEC, true);
if (signal_trampoline_region.is_error()) {
VERIFY_NOT_REACHED();
}
signal_trampoline_region.value()->set_syscall_region(true);
m_executable = main_program_description->custody();
m_arguments = arguments;
m_environment = environment;
m_veil_state = VeilState::None;
m_unveiled_paths.clear();
m_unveiled_paths.set_metadata({ "/", UnveilAccess::None, false });
for (auto& property : m_coredump_properties)
property = {};
auto current_thread = Thread::current();
current_thread->clear_signals();
clear_futex_queues_on_exec();
fds().change_each([&](auto& file_description_metadata) {
if (file_description_metadata.is_valid() && file_description_metadata.flags() & FD_CLOEXEC)
file_description_metadata = {};
});
int main_program_fd = -1;
if (interpreter_description) {
auto main_program_fd_wrapper = m_fds.allocate().release_value();
VERIFY(main_program_fd_wrapper.fd >= 0);
auto seek_result = main_program_description->seek(0, SEEK_SET);
VERIFY(!seek_result.is_error());
main_program_description->set_readable(true);
m_fds[main_program_fd_wrapper.fd].set(move(main_program_description), FD_CLOEXEC);
main_program_fd = main_program_fd_wrapper.fd;
}
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 auxv = generate_auxiliary_vector(load_result.load_base, load_result.entry_eip, uid(), euid(), gid(), egid(), path, main_program_fd);
// 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 make_stack_result = make_userspace_context_for_main_thread(new_main_thread->regs(), *load_result.stack_region.unsafe_ptr(), move(arguments), move(environment), move(auxv));
if (make_stack_result.is_error())
return make_stack_result.error();
FlatPtr new_userspace_sp = make_stack_result.value();
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);
}
// 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!
m_name = parts.take_last();
new_main_thread->set_name(KString::try_create(m_name));
{
ProtectedDataMutationScope scope { *this };
m_protected_values.promises = m_protected_values.execpromises.load();
m_protected_values.has_promises = m_protected_values.has_execpromises.load();
m_protected_values.execpromises = 0;
m_protected_values.has_execpromises = false;
m_protected_values.signal_trampoline = signal_trampoline_region.value()->vaddr();
// FIXME: PID/TID ISSUE
m_protected_values.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;
#if ARCH(I386)
regs.cs = GDT_SELECTOR_CODE3 | 3;
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);
}
{
ScopedSpinLock lock(g_scheduler_lock);
new_main_thread->set_state(Thread::State::Runnable);
}
u32 lock_count_to_restore;
[[maybe_unused]] auto rc = big_lock().force_unlock_if_locked(lock_count_to_restore);
VERIFY_INTERRUPTS_DISABLED();
VERIFY(Processor::in_critical());
return KSuccess;
}
static Vector<ELF::AuxiliaryValue> generate_auxiliary_vector(FlatPtr load_base, FlatPtr entry_eip, uid_t uid, uid_t euid, gid_t gid, gid_t egid, String executable_path, int main_program_fd)
{
Vector<ELF::AuxiliaryValue> auxv;
// PHDR/EXECFD
// PH*
auxv.append({ ELF::AuxiliaryValue::PageSize, PAGE_SIZE });
auxv.append({ ELF::AuxiliaryValue::BaseAddress, (void*)load_base });
auxv.append({ ELF::AuxiliaryValue::Entry, (void*)entry_eip });
// NOTELF
auxv.append({ ELF::AuxiliaryValue::Uid, (long)uid });
auxv.append({ ELF::AuxiliaryValue::EUid, (long)euid });
auxv.append({ ELF::AuxiliaryValue::Gid, (long)gid });
auxv.append({ ELF::AuxiliaryValue::EGid, (long)egid });
auxv.append({ ELF::AuxiliaryValue::Platform, Processor::current().platform_string() });
// FIXME: This is platform specific
auxv.append({ ELF::AuxiliaryValue::HwCap, (long)CPUID(1).edx() });
auxv.append({ ELF::AuxiliaryValue::ClockTick, (long)TimeManagement::the().ticks_per_second() });
// FIXME: Also take into account things like extended filesystem permissions? That's what linux does...
auxv.append({ ELF::AuxiliaryValue::Secure, ((uid != euid) || (gid != egid)) ? 1 : 0 });
char random_bytes[16] {};
get_fast_random_bytes((u8*)random_bytes, sizeof(random_bytes));
auxv.append({ ELF::AuxiliaryValue::Random, String(random_bytes, sizeof(random_bytes)) });
auxv.append({ ELF::AuxiliaryValue::ExecFilename, executable_path });
auxv.append({ ELF::AuxiliaryValue::ExecFileDescriptor, main_program_fd });
auxv.append({ ELF::AuxiliaryValue::Null, 0L });
return auxv;
}
static KResultOr<Vector<String>> find_shebang_interpreter_for_executable(const char first_page[], int nread)
{
int word_start = 2;
int word_length = 0;
if (nread > 2 && first_page[0] == '#' && first_page[1] == '!') {
Vector<String> interpreter_words;
for (int 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) {
interpreter_words.append(String(&first_page[word_start], word_length));
}
word_length = 0;
word_start = i + 1;
}
}
if (word_length > 0)
interpreter_words.append(String(&first_page[word_start], word_length));
if (!interpreter_words.is_empty())
return interpreter_words;
}
return ENOEXEC;
}
KResultOr<RefPtr<FileDescription>> Process::find_elf_interpreter_for_executable(const String& path, const ElfW(Ehdr) & main_program_header, int nread, size_t file_size)
{
// Not using KResultOr here because we'll want to do the same thing in userspace in the RTLD
String interpreter_path;
if (!ELF::validate_program_headers(main_program_header, file_size, (const u8*)&main_program_header, nread, &interpreter_path)) {
dbgln("exec({}): File has invalid ELF Program headers", path);
return ENOEXEC;
}
if (!interpreter_path.is_empty()) {
dbgln_if(EXEC_DEBUG, "exec({}): Using program interpreter {}", path, interpreter_path);
auto interp_result = VirtualFileSystem::the().open(interpreter_path, O_EXEC, 0, current_directory());
if (interp_result.is_error()) {
dbgln("exec({}): Unable to open program interpreter {}", path, interpreter_path);
return interp_result.error();
}
auto interpreter_description = interp_result.value();
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_or_error = interpreter_description->read(first_page_buffer, sizeof(first_page));
if (nread_or_error.is_error())
return ENOEXEC;
nread = nread_or_error.value();
if (nread < (int)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_description->absolute_path());
return ENOEXEC;
}
// Not using KResultOr here because we'll want to do the same thing in userspace in the RTLD
String interpreter_interpreter_path;
if (!ELF::validate_program_headers(*elf_header, interp_metadata.size, (u8*)first_page, nread, &interpreter_interpreter_path)) {
dbgln("exec({}): Interpreter ({}) has invalid ELF Program headers", path, interpreter_description->absolute_path());
return ENOEXEC;
}
if (!interpreter_interpreter_path.is_empty()) {
dbgln("exec({}): Interpreter ({}) has its own interpreter ({})! No thank you!", path, interpreter_description->absolute_path(), interpreter_interpreter_path);
return ELOOP;
}
return interpreter_description;
}
if (main_program_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_program_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 KResult(KSuccess);
}
KResult Process::exec(String path, Vector<String> arguments, Vector<String> environment, 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 file_or_error = VirtualFileSystem::the().open(path, O_EXEC, 0, current_directory());
if (file_or_error.is_error())
return file_or_error.error();
auto description = file_or_error.release_value();
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_or_error = description->read(first_page_buffer, sizeof(first_page));
if (nread_or_error.is_error())
return ENOEXEC;
// 1) #! interpreted file
auto shebang_result = find_shebang_interpreter_for_executable(first_page, nread_or_error.value());
if (!shebang_result.is_error()) {
auto shebang_words = shebang_result.release_value();
auto shebang_path = shebang_words.first();
arguments[0] = move(path);
if (!arguments.try_prepend(move(shebang_words)))
return ENOMEM;
return exec(move(shebang_path), move(arguments), move(environment), ++recursion_depth);
}
// #2) ELF32 for i386
if (nread_or_error.value() < (int)sizeof(ElfW(Ehdr)))
return ENOEXEC;
auto 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 elf_result = find_elf_interpreter_for_executable(path, *main_program_header, nread_or_error.value(), metadata.size);
// Assume a static ELF executable by default
RefPtr<FileDescription> interpreter_description;
// We're getting either an interpreter, an error, or KSuccess (i.e. no interpreter but file checks out)
if (!elf_result.is_error()) {
// It's a dynamic ELF executable, with or without an interpreter. Do not allocate TLS
interpreter_description = elf_result.value();
} else if (elf_result.error().is_error())
return elf_result.error();
// 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 result = do_exec(move(description), move(arguments), move(environment), move(interpreter_description), new_main_thread, prev_flags, *main_program_header);
if (result.is_error())
return result;
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.own_lock());
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();
}
if (prev_flags & 0x200)
sti();
Processor::leave_critical();
return KSuccess;
}
KResultOr<FlatPtr> Process::sys$execve(Userspace<const Syscall::SC_execve_params*> user_params)
{
VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
REQUIRE_PROMISE(exec);
// NOTE: Be extremely careful with allocating any kernel memory in exec().
// On success, the kernel stack will be lost.
Syscall::SC_execve_params params;
if (!copy_from_user(&params, user_params))
return EFAULT;
if (params.arguments.length > ARG_MAX || params.environment.length > ARG_MAX)
return E2BIG;
String path;
{
auto path_arg = get_syscall_path_argument(params.path);
if (path_arg.is_error())
return path_arg.error();
path = path_arg.value()->view();
}
auto copy_user_strings = [](const auto& list, auto& output) {
if (!list.length)
return true;
Checked<size_t> size = sizeof(*list.strings);
size *= list.length;
if (size.has_overflow())
return false;
Vector<Syscall::StringArgument, 32> strings;
if (!strings.try_resize(list.length))
return false;
if (!copy_from_user(strings.data(), list.strings, size.value()))
return false;
for (size_t i = 0; i < list.length; ++i) {
auto string = copy_string_from_user(strings[i]);
if (string.is_null())
return false;
if (!output.try_append(move(string)))
return false;
}
return true;
};
Vector<String> arguments;
if (!copy_user_strings(params.arguments, arguments))
return EFAULT;
Vector<String> environment;
if (!copy_user_strings(params.environment, environment))
return EFAULT;
auto result = exec(move(path), move(arguments), move(environment));
VERIFY(result.is_error()); // We should never continue after a successful exec!
return result.error();
}
}
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