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>
12 #include <linux/sched/task_stack.h>
14 #include <linux/smp.h>
15 #include <linux/errno.h>
16 #include <linux/ptrace.h>
17 #include <linux/tracehook.h>
18 #include <linux/audit.h>
19 #include <linux/seccomp.h>
20 #include <linux/signal.h>
21 #include <linux/export.h>
22 #include <linux/context_tracking.h>
23 #include <linux/user-return-notifier.h>
24 #include <linux/uprobes.h>
25 #include <linux/livepatch.h>
28 #include <asm/traps.h>
30 #include <linux/uaccess.h>
31 #include <asm/cpufeature.h>
33 #define CREATE_TRACE_POINTS
34 #include <trace/events/syscalls.h>
36 #ifdef CONFIG_CONTEXT_TRACKING
37 /* Called on entry from user mode with IRQs off. */
38 __visible
inline void enter_from_user_mode(void)
40 CT_WARN_ON(ct_state() != CONTEXT_USER
);
44 static inline void enter_from_user_mode(void) {}
47 static void do_audit_syscall_entry(struct pt_regs
*regs
, u32 arch
)
50 if (arch
== AUDIT_ARCH_X86_64
) {
51 audit_syscall_entry(regs
->orig_ax
, regs
->di
,
52 regs
->si
, regs
->dx
, regs
->r10
);
56 audit_syscall_entry(regs
->orig_ax
, regs
->bx
,
57 regs
->cx
, regs
->dx
, regs
->si
);
62 * Returns the syscall nr to run (which should match regs->orig_ax) or -1
63 * to skip the syscall.
65 static long syscall_trace_enter(struct pt_regs
*regs
)
67 u32 arch
= in_ia32_syscall() ? AUDIT_ARCH_I386
: AUDIT_ARCH_X86_64
;
69 struct thread_info
*ti
= current_thread_info();
70 unsigned long ret
= 0;
71 bool emulated
= false;
74 if (IS_ENABLED(CONFIG_DEBUG_ENTRY
))
75 BUG_ON(regs
!= task_pt_regs(current
));
77 work
= ACCESS_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
;
79 if (unlikely(work
& _TIF_SYSCALL_EMU
))
82 if ((emulated
|| (work
& _TIF_SYSCALL_TRACE
)) &&
83 tracehook_report_syscall_entry(regs
))
91 * Do seccomp after ptrace, to catch any tracer changes.
93 if (work
& _TIF_SECCOMP
) {
94 struct seccomp_data sd
;
97 sd
.nr
= regs
->orig_ax
;
98 sd
.instruction_pointer
= regs
->ip
;
100 if (arch
== AUDIT_ARCH_X86_64
) {
101 sd
.args
[0] = regs
->di
;
102 sd
.args
[1] = regs
->si
;
103 sd
.args
[2] = regs
->dx
;
104 sd
.args
[3] = regs
->r10
;
105 sd
.args
[4] = regs
->r8
;
106 sd
.args
[5] = regs
->r9
;
110 sd
.args
[0] = regs
->bx
;
111 sd
.args
[1] = regs
->cx
;
112 sd
.args
[2] = regs
->dx
;
113 sd
.args
[3] = regs
->si
;
114 sd
.args
[4] = regs
->di
;
115 sd
.args
[5] = regs
->bp
;
118 ret
= __secure_computing(&sd
);
124 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT
)))
125 trace_sys_enter(regs
, regs
->orig_ax
);
127 do_audit_syscall_entry(regs
, arch
);
129 return ret
?: regs
->orig_ax
;
132 #define EXIT_TO_USERMODE_LOOP_FLAGS \
133 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
134 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
136 static void exit_to_usermode_loop(struct pt_regs
*regs
, u32 cached_flags
)
139 * In order to return to user mode, we need to have IRQs off with
140 * none of EXIT_TO_USERMODE_LOOP_FLAGS set. Several of these flags
141 * can be set at any time on preemptable kernels if we have IRQs on,
142 * so we need to loop. Disabling preemption wouldn't help: doing the
143 * work to clear some of the flags can sleep.
146 /* We have work to do. */
149 if (cached_flags
& _TIF_NEED_RESCHED
)
152 if (cached_flags
& _TIF_UPROBE
)
153 uprobe_notify_resume(regs
);
155 /* deal with pending signal delivery */
156 if (cached_flags
& _TIF_SIGPENDING
)
159 if (cached_flags
& _TIF_NOTIFY_RESUME
) {
160 clear_thread_flag(TIF_NOTIFY_RESUME
);
161 tracehook_notify_resume(regs
);
164 if (cached_flags
& _TIF_USER_RETURN_NOTIFY
)
165 fire_user_return_notifiers();
167 if (cached_flags
& _TIF_PATCH_PENDING
)
168 klp_update_patch_state(current
);
170 /* Disable IRQs and retry */
173 cached_flags
= READ_ONCE(current_thread_info()->flags
);
175 if (!(cached_flags
& EXIT_TO_USERMODE_LOOP_FLAGS
))
180 /* Called with IRQs disabled. */
181 __visible
inline void prepare_exit_to_usermode(struct pt_regs
*regs
)
183 struct thread_info
*ti
= current_thread_info();
186 if (IS_ENABLED(CONFIG_PROVE_LOCKING
) && WARN_ON(!irqs_disabled()))
191 cached_flags
= READ_ONCE(ti
->flags
);
193 if (unlikely(cached_flags
& EXIT_TO_USERMODE_LOOP_FLAGS
))
194 exit_to_usermode_loop(regs
, cached_flags
);
198 * Compat syscalls set TS_COMPAT. Make sure we clear it before
199 * returning to user mode. We need to clear it *after* signal
200 * handling, because syscall restart has a fixup for compat
201 * syscalls. The fixup is exercised by the ptrace_syscall_32
204 * We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
205 * special case only applies after poking regs and before the
206 * very next return to user mode.
208 current
->thread
.status
&= ~(TS_COMPAT
|TS_I386_REGS_POKED
);
214 #define SYSCALL_EXIT_WORK_FLAGS \
215 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
216 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
218 static void syscall_slow_exit_work(struct pt_regs
*regs
, u32 cached_flags
)
222 audit_syscall_exit(regs
);
224 if (cached_flags
& _TIF_SYSCALL_TRACEPOINT
)
225 trace_sys_exit(regs
, regs
->ax
);
228 * If TIF_SYSCALL_EMU is set, we only get here because of
229 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
230 * We already reported this syscall instruction in
231 * syscall_trace_enter().
234 (cached_flags
& (_TIF_SINGLESTEP
| _TIF_SYSCALL_EMU
))
236 if (step
|| cached_flags
& _TIF_SYSCALL_TRACE
)
237 tracehook_report_syscall_exit(regs
, step
);
241 * Called with IRQs on and fully valid regs. Returns with IRQs off in a
242 * state such that we can immediately switch to user mode.
244 __visible
inline void syscall_return_slowpath(struct pt_regs
*regs
)
246 struct thread_info
*ti
= current_thread_info();
247 u32 cached_flags
= READ_ONCE(ti
->flags
);
249 CT_WARN_ON(ct_state() != CONTEXT_KERNEL
);
251 if (IS_ENABLED(CONFIG_PROVE_LOCKING
) &&
252 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs
->orig_ax
))
256 * First do one-time work. If these work items are enabled, we
257 * want to run them exactly once per syscall exit with IRQs on.
259 if (unlikely(cached_flags
& SYSCALL_EXIT_WORK_FLAGS
))
260 syscall_slow_exit_work(regs
, cached_flags
);
263 prepare_exit_to_usermode(regs
);
267 __visible
void do_syscall_64(struct pt_regs
*regs
)
269 struct thread_info
*ti
= current_thread_info();
270 unsigned long nr
= regs
->orig_ax
;
272 enter_from_user_mode();
275 if (READ_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
)
276 nr
= syscall_trace_enter(regs
);
279 * NB: Native and x32 syscalls are dispatched from the same
280 * table. The only functional difference is the x32 bit in
281 * regs->orig_ax, which changes the behavior of some syscalls.
283 if (likely((nr
& __SYSCALL_MASK
) < NR_syscalls
)) {
284 regs
->ax
= sys_call_table
[nr
& __SYSCALL_MASK
](
285 regs
->di
, regs
->si
, regs
->dx
,
286 regs
->r10
, regs
->r8
, regs
->r9
);
289 syscall_return_slowpath(regs
);
293 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
295 * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
296 * all entry and exit work and returns with IRQs off. This function is
297 * extremely hot in workloads that use it, and it's usually called from
298 * do_fast_syscall_32, so forcibly inline it to improve performance.
300 static __always_inline
void do_syscall_32_irqs_on(struct pt_regs
*regs
)
302 struct thread_info
*ti
= current_thread_info();
303 unsigned int nr
= (unsigned int)regs
->orig_ax
;
305 #ifdef CONFIG_IA32_EMULATION
306 current
->thread
.status
|= TS_COMPAT
;
309 if (READ_ONCE(ti
->flags
) & _TIF_WORK_SYSCALL_ENTRY
) {
311 * Subtlety here: if ptrace pokes something larger than
312 * 2^32-1 into orig_ax, this truncates it. This may or
313 * may not be necessary, but it matches the old asm
316 nr
= syscall_trace_enter(regs
);
319 if (likely(nr
< IA32_NR_syscalls
)) {
321 * It's possible that a 32-bit syscall implementation
322 * takes a 64-bit parameter but nonetheless assumes that
323 * the high bits are zero. Make sure we zero-extend all
326 regs
->ax
= ia32_sys_call_table
[nr
](
327 (unsigned int)regs
->bx
, (unsigned int)regs
->cx
,
328 (unsigned int)regs
->dx
, (unsigned int)regs
->si
,
329 (unsigned int)regs
->di
, (unsigned int)regs
->bp
);
332 syscall_return_slowpath(regs
);
335 /* Handles int $0x80 */
336 __visible
void do_int80_syscall_32(struct pt_regs
*regs
)
338 enter_from_user_mode();
340 do_syscall_32_irqs_on(regs
);
343 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
344 __visible
long do_fast_syscall_32(struct pt_regs
*regs
)
347 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
348 * convention. Adjust regs so it looks like we entered using int80.
351 unsigned long landing_pad
= (unsigned long)current
->mm
->context
.vdso
+
352 vdso_image_32
.sym_int80_landing_pad
;
355 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
356 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
359 regs
->ip
= landing_pad
;
361 enter_from_user_mode();
365 /* Fetch EBP from where the vDSO stashed it. */
369 * Micro-optimization: the pointer we're following is explicitly
370 * 32 bits, so it can't be out of range.
372 __get_user(*(u32
*)®s
->bp
,
373 (u32 __user __force
*)(unsigned long)(u32
)regs
->sp
)
375 get_user(*(u32
*)®s
->bp
,
376 (u32 __user __force
*)(unsigned long)(u32
)regs
->sp
)
380 /* User code screwed up. */
383 prepare_exit_to_usermode(regs
);
384 return 0; /* Keep it simple: use IRET. */
387 /* Now this is just like a normal syscall. */
388 do_syscall_32_irqs_on(regs
);
392 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
393 * SYSRETL is available on all 64-bit CPUs, so we don't need to
394 * bother with SYSEXIT.
396 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
397 * because the ECX fixup above will ensure that this is essentially
400 return regs
->cs
== __USER32_CS
&& regs
->ss
== __USER_DS
&&
401 regs
->ip
== landing_pad
&&
402 (regs
->flags
& (X86_EFLAGS_RF
| X86_EFLAGS_TF
)) == 0;
405 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
407 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
408 * because the ECX fixup above will ensure that this is essentially
411 * We don't allow syscalls at all from VM86 mode, but we still
412 * need to check VM, because we might be returning from sys_vm86.
414 return static_cpu_has(X86_FEATURE_SEP
) &&
415 regs
->cs
== __USER_CS
&& regs
->ss
== __USER_DS
&&
416 regs
->ip
== landing_pad
&&
417 (regs
->flags
& (X86_EFLAGS_RF
| X86_EFLAGS_TF
| X86_EFLAGS_VM
)) == 0;