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/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <Kernel/API/Syscall.h>
#include <Kernel/Arch/x86/CPU.h>
#include <Kernel/Panic.h>
#include <Kernel/Process.h>
#include <Kernel/ThreadTracer.h>
#include <Kernel/VM/MemoryManager.h>
namespace Kernel {
extern "C" void syscall_handler(TrapFrame*) __attribute__((used));
extern "C" void syscall_asm_entry();
// clang-format off
#if ARCH(I386)
asm(
".globl syscall_asm_entry\n"
"syscall_asm_entry:\n"
" pushl $0x0\n"
" pusha\n"
" pushl %ds\n"
" pushl %es\n"
" pushl %fs\n"
" pushl %gs\n"
" pushl %ss\n"
" mov $" __STRINGIFY(GDT_SELECTOR_DATA0) ", %ax\n"
" mov %ax, %ds\n"
" mov %ax, %es\n"
" mov $" __STRINGIFY(GDT_SELECTOR_PROC) ", %ax\n"
" mov %ax, %fs\n"
" cld\n"
" xor %esi, %esi\n"
" xor %edi, %edi\n"
" pushl %esp \n" // set TrapFrame::regs
" subl $" __STRINGIFY(TRAP_FRAME_SIZE - 4) ", %esp \n"
" movl %esp, %ebx \n"
" pushl %ebx \n" // push pointer to TrapFrame
" call enter_trap_no_irq \n"
" movl %ebx, 0(%esp) \n" // push pointer to TrapFrame
" call syscall_handler \n"
" movl %ebx, 0(%esp) \n" // push pointer to TrapFrame
" jmp common_trap_exit \n");
#elif ARCH(X86_64)
asm(
".globl syscall_asm_entry\n"
"syscall_asm_entry:\n"
" cli\n"
" hlt\n");
#endif
// clang-format on
namespace Syscall {
static KResultOr<FlatPtr> handle(RegisterState&, FlatPtr function, FlatPtr arg1, FlatPtr arg2, FlatPtr arg3);
UNMAP_AFTER_INIT void initialize()
{
register_user_callable_interrupt_handler(syscall_vector, syscall_asm_entry);
}
#pragma GCC diagnostic ignored "-Wcast-function-type"
typedef KResultOr<FlatPtr> (Process::*Handler)(FlatPtr, FlatPtr, FlatPtr);
typedef KResultOr<FlatPtr> (Process::*HandlerWithRegisterState)(RegisterState&);
#define __ENUMERATE_SYSCALL(x) reinterpret_cast<Handler>(&Process::sys$##x),
static const Handler s_syscall_table[] = {
ENUMERATE_SYSCALLS(__ENUMERATE_SYSCALL)
};
#undef __ENUMERATE_SYSCALL
KResultOr<FlatPtr> handle(RegisterState& regs, FlatPtr function, FlatPtr arg1, FlatPtr arg2, FlatPtr arg3)
{
VERIFY_INTERRUPTS_ENABLED();
auto current_thread = Thread::current();
auto& process = current_thread->process();
current_thread->did_syscall();
if (function == SC_exit || function == SC_exit_thread) {
// These syscalls need special handling since they never return to the caller.
if (auto* tracer = process.tracer(); tracer && tracer->is_tracing_syscalls()) {
regs.eax = 0;
tracer->set_trace_syscalls(false);
process.tracer_trap(*current_thread, regs); // this triggers SIGTRAP and stops the thread!
}
switch (function) {
case SC_exit:
process.sys$exit(arg1);
break;
case SC_exit_thread:
process.sys$exit_thread(arg1);
break;
default:
VERIFY_NOT_REACHED();
}
}
if (function == SC_fork || function == SC_sigreturn) {
// These syscalls want the RegisterState& rather than individual parameters.
auto handler = (HandlerWithRegisterState)s_syscall_table[function];
return (process.*(handler))(regs);
}
if (function >= Function::__Count) {
dbgln("Unknown syscall {} requested ({:08x}, {:08x}, {:08x})", function, arg1, arg2, arg3);
return ENOSYS;
}
if (s_syscall_table[function] == nullptr) {
dbgln("Null syscall {} requested, you probably need to rebuild this program!", function);
return ENOSYS;
}
// This appears to be a bogus warning, as s_syscall_table is always
// initialized, and the index (function) is always bounded.
// TODO: Figure out how to avoid the suppression.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
return (process.*(s_syscall_table[function]))(arg1, arg2, arg3);
#pragma GCC diagnostic pop
}
}
NEVER_INLINE void syscall_handler(TrapFrame* trap)
{
auto& regs = *trap->regs;
auto current_thread = Thread::current();
VERIFY(current_thread->previous_mode() == Thread::PreviousMode::UserMode);
auto& process = current_thread->process();
if (auto tracer = process.tracer(); tracer && tracer->is_tracing_syscalls()) {
tracer->set_trace_syscalls(false);
process.tracer_trap(*current_thread, regs); // this triggers SIGTRAP and stops the thread!
}
current_thread->yield_if_stopped();
// Make sure SMAP protection is enabled on syscall entry.
clac();
// Apply a random offset in the range 0-255 to the stack pointer,
// to make kernel stacks a bit less deterministic.
u32 lsw;
u32 msw;
read_tsc(lsw, msw);
auto* ptr = (char*)__builtin_alloca(lsw & 0xff);
asm volatile(""
: "=m"(*ptr));
static constexpr FlatPtr iopl_mask = 3u << 12;
if ((regs.eflags & (iopl_mask)) != 0) {
PANIC("Syscall from process with IOPL != 0");
}
// NOTE: We take the big process lock before inspecting memory regions.
process.big_lock().lock();
if (!MM.validate_user_stack(process, VirtualAddress(regs.userspace_esp))) {
dbgln("Invalid stack pointer: {:p}", regs.userspace_esp);
handle_crash(regs, "Bad stack on syscall entry", SIGSTKFLT);
}
auto* calling_region = MM.find_user_region_from_vaddr(process.space(), VirtualAddress(regs.eip));
if (!calling_region) {
dbgln("Syscall from {:p} which has no associated region", regs.eip);
handle_crash(regs, "Syscall from unknown region", SIGSEGV);
}
if (calling_region->is_writable()) {
dbgln("Syscall from writable memory at {:p}", regs.eip);
handle_crash(regs, "Syscall from writable memory", SIGSEGV);
}
if (process.space().enforces_syscall_regions() && !calling_region->is_syscall_region()) {
dbgln("Syscall from non-syscall region");
handle_crash(regs, "Syscall from non-syscall region", SIGSEGV);
}
auto function = regs.eax;
auto arg1 = regs.edx;
auto arg2 = regs.ecx;
auto arg3 = regs.ebx;
auto result = Syscall::handle(regs, function, arg1, arg2, arg3);
if (result.is_error())
regs.eax = result.error();
else
regs.eax = result.value();
process.big_lock().unlock();
if (auto tracer = process.tracer(); tracer && tracer->is_tracing_syscalls()) {
tracer->set_trace_syscalls(false);
process.tracer_trap(*current_thread, regs); // this triggers SIGTRAP and stops the thread!
}
current_thread->yield_if_stopped();
current_thread->check_dispatch_pending_signal();
// If the previous mode somehow changed something is seriously messed up...
VERIFY(current_thread->previous_mode() == Thread::PreviousMode::UserMode);
// Check if we're supposed to return to userspace or just die.
current_thread->die_if_needed();
VERIFY(!g_scheduler_lock.own_lock());
}
}
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