blob: 51beb8d29123a66f28e1d4d6e0f35c160a9913f7 [file] [log] [blame]
/*
* common.c - C code for kernel entry and exit
* Copyright (c) 2015 Andrew Lutomirski
* GPL v2
*
* Based on asm and ptrace code by many authors. The code here originated
* in ptrace.c and signal.c.
*/
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
#include <linux/audit.h>
#include <linux/seccomp.h>
#include <linux/signal.h>
#include <linux/export.h>
#include <linux/context_tracking.h>
#include <linux/user-return-notifier.h>
#include <linux/nospec.h>
#include <linux/uprobes.h>
#include <linux/livepatch.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <asm/desc.h>
#include <asm/traps.h>
#include <asm/vdso.h>
#include <asm/cpufeature.h>
#include <asm/fpu/api.h>
#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
#ifdef CONFIG_CONTEXT_TRACKING
/* Called on entry from user mode with IRQs off. */
__visible inline void enter_from_user_mode(void)
{
CT_WARN_ON(ct_state() != CONTEXT_USER);
user_exit_irqoff();
}
#else
static inline void enter_from_user_mode(void) {}
#endif
static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
{
#ifdef CONFIG_X86_64
if (arch == AUDIT_ARCH_X86_64) {
audit_syscall_entry(regs->orig_ax, regs->di,
regs->si, regs->dx, regs->r10);
} else
#endif
{
audit_syscall_entry(regs->orig_ax, regs->bx,
regs->cx, regs->dx, regs->si);
}
}
/*
* Returns the syscall nr to run (which should match regs->orig_ax) or -1
* to skip the syscall.
*/
static long syscall_trace_enter(struct pt_regs *regs)
{
u32 arch = in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
struct thread_info *ti = current_thread_info();
unsigned long ret = 0;
bool emulated = false;
u32 work;
if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
BUG_ON(regs != task_pt_regs(current));
work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
if (unlikely(work & _TIF_SYSCALL_EMU))
emulated = true;
if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
tracehook_report_syscall_entry(regs))
return -1L;
if (emulated)
return -1L;
#ifdef CONFIG_SECCOMP
/*
* Do seccomp after ptrace, to catch any tracer changes.
*/
if (work & _TIF_SECCOMP) {
struct seccomp_data sd;
sd.arch = arch;
sd.nr = regs->orig_ax;
sd.instruction_pointer = regs->ip;
#ifdef CONFIG_X86_64
if (arch == AUDIT_ARCH_X86_64) {
sd.args[0] = regs->di;
sd.args[1] = regs->si;
sd.args[2] = regs->dx;
sd.args[3] = regs->r10;
sd.args[4] = regs->r8;
sd.args[5] = regs->r9;
} else
#endif
{
sd.args[0] = regs->bx;
sd.args[1] = regs->cx;
sd.args[2] = regs->dx;
sd.args[3] = regs->si;
sd.args[4] = regs->di;
sd.args[5] = regs->bp;
}
ret = __secure_computing(&sd);
if (ret == -1)
return ret;
}
#endif
if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
trace_sys_enter(regs, regs->orig_ax);
do_audit_syscall_entry(regs, arch);
return ret ?: regs->orig_ax;
}
#define EXIT_TO_USERMODE_LOOP_FLAGS \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
_TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
{
/*
* In order to return to user mode, we need to have IRQs off with
* none of EXIT_TO_USERMODE_LOOP_FLAGS set. Several of these flags
* can be set at any time on preemptible kernels if we have IRQs on,
* so we need to loop. Disabling preemption wouldn't help: doing the
* work to clear some of the flags can sleep.
*/
while (true) {
/* We have work to do. */
local_irq_enable();
if (cached_flags & _TIF_NEED_RESCHED)
schedule();
if (cached_flags & _TIF_UPROBE)
uprobe_notify_resume(regs);
if (cached_flags & _TIF_PATCH_PENDING)
klp_update_patch_state(current);
/* deal with pending signal delivery */
if (cached_flags & _TIF_SIGPENDING)
do_signal(regs);
if (cached_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
rseq_handle_notify_resume(NULL, regs);
}
if (cached_flags & _TIF_USER_RETURN_NOTIFY)
fire_user_return_notifiers();
/* Disable IRQs and retry */
local_irq_disable();
cached_flags = READ_ONCE(current_thread_info()->flags);
if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
break;
}
}
/* Called with IRQs disabled. */
__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
{
struct thread_info *ti = current_thread_info();
u32 cached_flags;
addr_limit_user_check();
lockdep_assert_irqs_disabled();
lockdep_sys_exit();
cached_flags = READ_ONCE(ti->flags);
if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
exit_to_usermode_loop(regs, cached_flags);
/* Reload ti->flags; we may have rescheduled above. */
cached_flags = READ_ONCE(ti->flags);
fpregs_assert_state_consistent();
if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
switch_fpu_return();
#ifdef CONFIG_COMPAT
/*
* Compat syscalls set TS_COMPAT. Make sure we clear it before
* returning to user mode. We need to clear it *after* signal
* handling, because syscall restart has a fixup for compat
* syscalls. The fixup is exercised by the ptrace_syscall_32
* selftest.
*
* We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
* special case only applies after poking regs and before the
* very next return to user mode.
*/
ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
#endif
user_enter_irqoff();
}
#define SYSCALL_EXIT_WORK_FLAGS \
(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
{
bool step;
audit_syscall_exit(regs);
if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
trace_sys_exit(regs, regs->ax);
/*
* If TIF_SYSCALL_EMU is set, we only get here because of
* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
* We already reported this syscall instruction in
* syscall_trace_enter().
*/
step = unlikely(
(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
== _TIF_SINGLESTEP);
if (step || cached_flags & _TIF_SYSCALL_TRACE)
tracehook_report_syscall_exit(regs, step);
}
/*
* Called with IRQs on and fully valid regs. Returns with IRQs off in a
* state such that we can immediately switch to user mode.
*/
__visible inline void syscall_return_slowpath(struct pt_regs *regs)
{
struct thread_info *ti = current_thread_info();
u32 cached_flags = READ_ONCE(ti->flags);
CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
local_irq_enable();
rseq_syscall(regs);
/*
* First do one-time work. If these work items are enabled, we
* want to run them exactly once per syscall exit with IRQs on.
*/
if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
syscall_slow_exit_work(regs, cached_flags);
local_irq_disable();
prepare_exit_to_usermode(regs);
}
#ifdef CONFIG_X86_64
__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
{
struct thread_info *ti;
enter_from_user_mode();
local_irq_enable();
ti = current_thread_info();
if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
nr = syscall_trace_enter(regs);
/*
* NB: Native and x32 syscalls are dispatched from the same
* table. The only functional difference is the x32 bit in
* regs->orig_ax, which changes the behavior of some syscalls.
*/
nr &= __SYSCALL_MASK;
if (likely(nr < NR_syscalls)) {
nr = array_index_nospec(nr, NR_syscalls);
regs->ax = sys_call_table[nr](regs);
}
syscall_return_slowpath(regs);
}
#endif
#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
/*
* Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
* all entry and exit work and returns with IRQs off. This function is
* extremely hot in workloads that use it, and it's usually called from
* do_fast_syscall_32, so forcibly inline it to improve performance.
*/
static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
{
struct thread_info *ti = current_thread_info();
unsigned int nr = (unsigned int)regs->orig_ax;
#ifdef CONFIG_IA32_EMULATION
ti->status |= TS_COMPAT;
#endif
if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
/*
* Subtlety here: if ptrace pokes something larger than
* 2^32-1 into orig_ax, this truncates it. This may or
* may not be necessary, but it matches the old asm
* behavior.
*/
nr = syscall_trace_enter(regs);
}
if (likely(nr < IA32_NR_syscalls)) {
nr = array_index_nospec(nr, IA32_NR_syscalls);
#ifdef CONFIG_IA32_EMULATION
regs->ax = ia32_sys_call_table[nr](regs);
#else
/*
* It's possible that a 32-bit syscall implementation
* takes a 64-bit parameter but nonetheless assumes that
* the high bits are zero. Make sure we zero-extend all
* of the args.
*/
regs->ax = ia32_sys_call_table[nr](
(unsigned int)regs->bx, (unsigned int)regs->cx,
(unsigned int)regs->dx, (unsigned int)regs->si,
(unsigned int)regs->di, (unsigned int)regs->bp);
#endif /* CONFIG_IA32_EMULATION */
}
syscall_return_slowpath(regs);
}
/* Handles int $0x80 */
__visible void do_int80_syscall_32(struct pt_regs *regs)
{
enter_from_user_mode();
local_irq_enable();
do_syscall_32_irqs_on(regs);
}
/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible long do_fast_syscall_32(struct pt_regs *regs)
{
/*
* Called using the internal vDSO SYSENTER/SYSCALL32 calling
* convention. Adjust regs so it looks like we entered using int80.
*/
unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
vdso_image_32.sym_int80_landing_pad;
/*
* SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
* so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
* Fix it up.
*/
regs->ip = landing_pad;
enter_from_user_mode();
local_irq_enable();
/* Fetch EBP from where the vDSO stashed it. */
if (
#ifdef CONFIG_X86_64
/*
* Micro-optimization: the pointer we're following is explicitly
* 32 bits, so it can't be out of range.
*/
__get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp)
#else
get_user(*(u32 *)&regs->bp,
(u32 __user __force *)(unsigned long)(u32)regs->sp)
#endif
) {
/* User code screwed up. */
local_irq_disable();
regs->ax = -EFAULT;
prepare_exit_to_usermode(regs);
return 0; /* Keep it simple: use IRET. */
}
/* Now this is just like a normal syscall. */
do_syscall_32_irqs_on(regs);
#ifdef CONFIG_X86_64
/*
* Opportunistic SYSRETL: if possible, try to return using SYSRETL.
* SYSRETL is available on all 64-bit CPUs, so we don't need to
* bother with SYSEXIT.
*
* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
* because the ECX fixup above will ensure that this is essentially
* never the case.
*/
return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
regs->ip == landing_pad &&
(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
#else
/*
* Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
*
* Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
* because the ECX fixup above will ensure that this is essentially
* never the case.
*
* We don't allow syscalls at all from VM86 mode, but we still
* need to check VM, because we might be returning from sys_vm86.
*/
return static_cpu_has(X86_FEATURE_SEP) &&
regs->cs == __USER_CS && regs->ss == __USER_DS &&
regs->ip == landing_pad &&
(regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
#endif
}
#endif