2 * common.c - C code for kernel entry and exit
3 * Copyright (c) 2015 Andrew Lutomirski
6 * Based on asm and ptrace code by many authors. The code here originated
7 * in ptrace.c and signal.c.
10 #include <linux/kernel.h>
11 #include <linux/sched.h>
13 #include <linux/smp.h>
14 #include <linux/errno.h>
15 #include <linux/ptrace.h>
16 #include <linux/tracehook.h>
17 #include <linux/audit.h>
18 #include <linux/seccomp.h>
19 #include <linux/signal.h>
20 #include <linux/export.h>
21 #include <linux/context_tracking.h>
22 #include <linux/user-return-notifier.h>
23 #include <linux/uprobes.h>
26 #include <asm/traps.h>
28 #include <asm/uaccess.h>
29 #include <asm/cpufeature.h>
31 #define CREATE_TRACE_POINTS
32 #include <trace/events/syscalls.h>
34 static struct thread_info
*pt_regs_to_thread_info(struct pt_regs
*regs
)
36 unsigned long top_of_stack
=
37 (unsigned long)(regs
+ 1) + TOP_OF_KERNEL_STACK_PADDING
;
38 return (struct thread_info
*)(top_of_stack
- THREAD_SIZE
);
41 #ifdef CONFIG_CONTEXT_TRACKING
42 /* Called on entry from user mode with IRQs off. */
43 __visible
void enter_from_user_mode(void)
45 CT_WARN_ON(ct_state() != CONTEXT_USER
);
50 static void do_audit_syscall_entry(struct pt_regs
*regs
, u32 arch
)
53 if (arch
== AUDIT_ARCH_X86_64
) {
54 audit_syscall_entry(regs
->orig_ax
, regs
->di
,
55 regs
->si
, regs
->dx
, regs
->r10
);
59 audit_syscall_entry(regs
->orig_ax
, regs
->bx
,
60 regs
->cx
, regs
->dx
, regs
->si
);
65 * We can return 0 to resume the syscall or anything else to go to phase
66 * 2. If we resume the syscall, we need to put something appropriate in
69 * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
70 * are fully functional.
72 * For phase 2's benefit, our return value is:
73 * 0: resume the syscall
74 * 1: go to phase 2; no seccomp phase 2 needed
75 * anything else: go to phase 2; pass return value to seccomp
77 unsigned long syscall_trace_enter_phase1(struct pt_regs
*regs
, u32 arch
)
79 struct thread_info
*ti
= pt_regs_to_thread_info(regs
);
80 unsigned long ret
= 0;
83 if (IS_ENABLED(CONFIG_DEBUG_ENTRY
))
84 BUG_ON(regs
!= task_pt_regs(current
));
86 work
= ACCESS_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
;
88 #ifdef CONFIG_CONTEXT_TRACKING
90 * If TIF_NOHZ is set, we are required to call user_exit() before
91 * doing anything that could touch RCU.
93 if (work
& _TIF_NOHZ
) {
94 enter_from_user_mode();
101 * Do seccomp first -- it should minimize exposure of other
102 * code, and keeping seccomp fast is probably more valuable
103 * than the rest of this.
105 if (work
& _TIF_SECCOMP
) {
106 struct seccomp_data sd
;
109 sd
.nr
= regs
->orig_ax
;
110 sd
.instruction_pointer
= regs
->ip
;
112 if (arch
== AUDIT_ARCH_X86_64
) {
113 sd
.args
[0] = regs
->di
;
114 sd
.args
[1] = regs
->si
;
115 sd
.args
[2] = regs
->dx
;
116 sd
.args
[3] = regs
->r10
;
117 sd
.args
[4] = regs
->r8
;
118 sd
.args
[5] = regs
->r9
;
122 sd
.args
[0] = regs
->bx
;
123 sd
.args
[1] = regs
->cx
;
124 sd
.args
[2] = regs
->dx
;
125 sd
.args
[3] = regs
->si
;
126 sd
.args
[4] = regs
->di
;
127 sd
.args
[5] = regs
->bp
;
130 BUILD_BUG_ON(SECCOMP_PHASE1_OK
!= 0);
131 BUILD_BUG_ON(SECCOMP_PHASE1_SKIP
!= 1);
133 ret
= seccomp_phase1(&sd
);
134 if (ret
== SECCOMP_PHASE1_SKIP
) {
137 } else if (ret
!= SECCOMP_PHASE1_OK
) {
138 return ret
; /* Go directly to phase 2 */
141 work
&= ~_TIF_SECCOMP
;
145 /* Do our best to finish without phase 2. */
147 return ret
; /* seccomp and/or nohz only (ret == 0 here) */
149 #ifdef CONFIG_AUDITSYSCALL
150 if (work
== _TIF_SYSCALL_AUDIT
) {
152 * If there is no more work to be done except auditing,
153 * then audit in phase 1. Phase 2 always audits, so, if
154 * we audit here, then we can't go on to phase 2.
156 do_audit_syscall_entry(regs
, arch
);
161 return 1; /* Something is enabled that we can't handle in phase 1 */
164 /* Returns the syscall nr to run (which should match regs->orig_ax). */
165 long syscall_trace_enter_phase2(struct pt_regs
*regs
, u32 arch
,
166 unsigned long phase1_result
)
168 struct thread_info
*ti
= pt_regs_to_thread_info(regs
);
170 u32 work
= ACCESS_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
;
172 if (IS_ENABLED(CONFIG_DEBUG_ENTRY
))
173 BUG_ON(regs
!= task_pt_regs(current
));
176 * If we stepped into a sysenter/syscall insn, it trapped in
177 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
178 * If user-mode had set TF itself, then it's still clear from
179 * do_debug() and we need to set it again to restore the user
180 * state. If we entered on the slow path, TF was already set.
182 if (work
& _TIF_SINGLESTEP
)
183 regs
->flags
|= X86_EFLAGS_TF
;
185 #ifdef CONFIG_SECCOMP
187 * Call seccomp_phase2 before running the other hooks so that
188 * they can see any changes made by a seccomp tracer.
190 if (phase1_result
> 1 && seccomp_phase2(phase1_result
)) {
191 /* seccomp failures shouldn't expose any additional code. */
196 if (unlikely(work
& _TIF_SYSCALL_EMU
))
199 if ((ret
|| test_thread_flag(TIF_SYSCALL_TRACE
)) &&
200 tracehook_report_syscall_entry(regs
))
203 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT
)))
204 trace_sys_enter(regs
, regs
->orig_ax
);
206 do_audit_syscall_entry(regs
, arch
);
208 return ret
?: regs
->orig_ax
;
211 long syscall_trace_enter(struct pt_regs
*regs
)
213 u32 arch
= is_ia32_task() ? AUDIT_ARCH_I386
: AUDIT_ARCH_X86_64
;
214 unsigned long phase1_result
= syscall_trace_enter_phase1(regs
, arch
);
216 if (phase1_result
== 0)
217 return regs
->orig_ax
;
219 return syscall_trace_enter_phase2(regs
, arch
, phase1_result
);
222 #define EXIT_TO_USERMODE_LOOP_FLAGS \
223 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
224 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
226 static void exit_to_usermode_loop(struct pt_regs
*regs
, u32 cached_flags
)
229 * In order to return to user mode, we need to have IRQs off with
230 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
231 * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags
232 * can be set at any time on preemptable kernels if we have IRQs on,
233 * so we need to loop. Disabling preemption wouldn't help: doing the
234 * work to clear some of the flags can sleep.
237 /* We have work to do. */
240 if (cached_flags
& _TIF_NEED_RESCHED
)
243 if (cached_flags
& _TIF_UPROBE
)
244 uprobe_notify_resume(regs
);
246 /* deal with pending signal delivery */
247 if (cached_flags
& _TIF_SIGPENDING
)
250 if (cached_flags
& _TIF_NOTIFY_RESUME
) {
251 clear_thread_flag(TIF_NOTIFY_RESUME
);
252 tracehook_notify_resume(regs
);
255 if (cached_flags
& _TIF_USER_RETURN_NOTIFY
)
256 fire_user_return_notifiers();
258 /* Disable IRQs and retry */
261 cached_flags
= READ_ONCE(pt_regs_to_thread_info(regs
)->flags
);
263 if (!(cached_flags
& EXIT_TO_USERMODE_LOOP_FLAGS
))
269 /* Called with IRQs disabled. */
270 __visible
inline void prepare_exit_to_usermode(struct pt_regs
*regs
)
272 struct thread_info
*ti
= pt_regs_to_thread_info(regs
);
275 if (IS_ENABLED(CONFIG_PROVE_LOCKING
) && WARN_ON(!irqs_disabled()))
280 cached_flags
= READ_ONCE(ti
->flags
);
282 if (unlikely(cached_flags
& EXIT_TO_USERMODE_LOOP_FLAGS
))
283 exit_to_usermode_loop(regs
, cached_flags
);
287 * Compat syscalls set TS_COMPAT. Make sure we clear it before
288 * returning to user mode. We need to clear it *after* signal
289 * handling, because syscall restart has a fixup for compat
290 * syscalls. The fixup is exercised by the ptrace_syscall_32
293 ti
->status
&= ~TS_COMPAT
;
299 #define SYSCALL_EXIT_WORK_FLAGS \
300 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
301 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
303 static void syscall_slow_exit_work(struct pt_regs
*regs
, u32 cached_flags
)
307 audit_syscall_exit(regs
);
309 if (cached_flags
& _TIF_SYSCALL_TRACEPOINT
)
310 trace_sys_exit(regs
, regs
->ax
);
313 * If TIF_SYSCALL_EMU is set, we only get here because of
314 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
315 * We already reported this syscall instruction in
316 * syscall_trace_enter().
319 (cached_flags
& (_TIF_SINGLESTEP
| _TIF_SYSCALL_EMU
))
321 if (step
|| cached_flags
& _TIF_SYSCALL_TRACE
)
322 tracehook_report_syscall_exit(regs
, step
);
326 * Called with IRQs on and fully valid regs. Returns with IRQs off in a
327 * state such that we can immediately switch to user mode.
329 __visible
inline void syscall_return_slowpath(struct pt_regs
*regs
)
331 struct thread_info
*ti
= pt_regs_to_thread_info(regs
);
332 u32 cached_flags
= READ_ONCE(ti
->flags
);
334 CT_WARN_ON(ct_state() != CONTEXT_KERNEL
);
336 if (IS_ENABLED(CONFIG_PROVE_LOCKING
) &&
337 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs
->orig_ax
))
341 * First do one-time work. If these work items are enabled, we
342 * want to run them exactly once per syscall exit with IRQs on.
344 if (unlikely(cached_flags
& SYSCALL_EXIT_WORK_FLAGS
))
345 syscall_slow_exit_work(regs
, cached_flags
);
348 prepare_exit_to_usermode(regs
);
352 __visible
void do_syscall_64(struct pt_regs
*regs
)
354 struct thread_info
*ti
= pt_regs_to_thread_info(regs
);
355 unsigned long nr
= regs
->orig_ax
;
359 if (READ_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
)
360 nr
= syscall_trace_enter(regs
);
363 * NB: Native and x32 syscalls are dispatched from the same
364 * table. The only functional difference is the x32 bit in
365 * regs->orig_ax, which changes the behavior of some syscalls.
367 if (likely((nr
& __SYSCALL_MASK
) < NR_syscalls
)) {
368 regs
->ax
= sys_call_table
[nr
& __SYSCALL_MASK
](
369 regs
->di
, regs
->si
, regs
->dx
,
370 regs
->r10
, regs
->r8
, regs
->r9
);
373 syscall_return_slowpath(regs
);
377 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
379 * Does a 32-bit syscall. Called with IRQs on and does all entry and
380 * exit work and returns with IRQs off. This function is extremely hot
381 * in workloads that use it, and it's usually called from
382 * do_fast_syscall_32, so forcibly inline it to improve performance.
385 /* 32-bit kernels use a trap gate for INT80, and the asm code calls here. */
388 /* 64-bit kernels use do_syscall_32_irqs_off() instead. */
391 __always_inline
void do_syscall_32_irqs_on(struct pt_regs
*regs
)
393 struct thread_info
*ti
= pt_regs_to_thread_info(regs
);
394 unsigned int nr
= (unsigned int)regs
->orig_ax
;
396 #ifdef CONFIG_IA32_EMULATION
397 ti
->status
|= TS_COMPAT
;
400 if (READ_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
) {
402 * Subtlety here: if ptrace pokes something larger than
403 * 2^32-1 into orig_ax, this truncates it. This may or
404 * may not be necessary, but it matches the old asm
407 nr
= syscall_trace_enter(regs
);
410 if (likely(nr
< IA32_NR_syscalls
)) {
412 * It's possible that a 32-bit syscall implementation
413 * takes a 64-bit parameter but nonetheless assumes that
414 * the high bits are zero. Make sure we zero-extend all
417 regs
->ax
= ia32_sys_call_table
[nr
](
418 (unsigned int)regs
->bx
, (unsigned int)regs
->cx
,
419 (unsigned int)regs
->dx
, (unsigned int)regs
->si
,
420 (unsigned int)regs
->di
, (unsigned int)regs
->bp
);
423 syscall_return_slowpath(regs
);
427 /* Handles INT80 on 64-bit kernels */
428 __visible
void do_syscall_32_irqs_off(struct pt_regs
*regs
)
431 do_syscall_32_irqs_on(regs
);
435 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
436 __visible
long do_fast_syscall_32(struct pt_regs
*regs
)
439 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
440 * convention. Adjust regs so it looks like we entered using int80.
443 unsigned long landing_pad
= (unsigned long)current
->mm
->context
.vdso
+
444 vdso_image_32
.sym_int80_landing_pad
;
447 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
448 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
451 regs
->ip
= landing_pad
;
454 * Fetch EBP from where the vDSO stashed it.
456 * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
462 * Micro-optimization: the pointer we're following is explicitly
463 * 32 bits, so it can't be out of range.
465 __get_user(*(u32
*)®s
->bp
,
466 (u32 __user __force
*)(unsigned long)(u32
)regs
->sp
)
468 get_user(*(u32
*)®s
->bp
,
469 (u32 __user __force
*)(unsigned long)(u32
)regs
->sp
)
473 /* User code screwed up. */
476 #ifdef CONFIG_CONTEXT_TRACKING
477 enter_from_user_mode();
479 prepare_exit_to_usermode(regs
);
480 return 0; /* Keep it simple: use IRET. */
483 /* Now this is just like a normal syscall. */
484 do_syscall_32_irqs_on(regs
);
488 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
489 * SYSRETL is available on all 64-bit CPUs, so we don't need to
490 * bother with SYSEXIT.
492 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
493 * because the ECX fixup above will ensure that this is essentially
496 return regs
->cs
== __USER32_CS
&& regs
->ss
== __USER_DS
&&
497 regs
->ip
== landing_pad
&&
498 (regs
->flags
& (X86_EFLAGS_RF
| X86_EFLAGS_TF
)) == 0;
501 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
503 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
504 * because the ECX fixup above will ensure that this is essentially
507 * We don't allow syscalls at all from VM86 mode, but we still
508 * need to check VM, because we might be returning from sys_vm86.
510 return static_cpu_has(X86_FEATURE_SEP
) &&
511 regs
->cs
== __USER_CS
&& regs
->ss
== __USER_DS
&&
512 regs
->ip
== landing_pad
&&
513 (regs
->flags
& (X86_EFLAGS_RF
| X86_EFLAGS_TF
| X86_EFLAGS_VM
)) == 0;