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Andy Lutomirski1f484aa2015-07-03 12:44:23 -07001/*
2 * common.c - C code for kernel entry and exit
3 * Copyright (c) 2015 Andrew Lutomirski
4 * GPL v2
5 *
6 * Based on asm and ptrace code by many authors. The code here originated
7 * in ptrace.c and signal.c.
8 */
9
10#include <linux/kernel.h>
11#include <linux/sched.h>
12#include <linux/mm.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>
24
25#include <asm/desc.h>
26#include <asm/traps.h>
Andy Lutomirski710246d2015-10-05 17:48:10 -070027#include <asm/vdso.h>
28#include <asm/uaccess.h>
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070029
30#define CREATE_TRACE_POINTS
31#include <trace/events/syscalls.h>
32
Andy Lutomirskidd636072015-10-05 17:48:22 -070033static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
34{
35 unsigned long top_of_stack =
36 (unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
37 return (struct thread_info *)(top_of_stack - THREAD_SIZE);
38}
39
Andy Lutomirskifeed36c2015-07-03 12:44:25 -070040#ifdef CONFIG_CONTEXT_TRACKING
41/* Called on entry from user mode with IRQs off. */
42__visible void enter_from_user_mode(void)
43{
44 CT_WARN_ON(ct_state() != CONTEXT_USER);
45 user_exit();
46}
47#endif
48
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070049static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
50{
51#ifdef CONFIG_X86_64
52 if (arch == AUDIT_ARCH_X86_64) {
53 audit_syscall_entry(regs->orig_ax, regs->di,
54 regs->si, regs->dx, regs->r10);
55 } else
56#endif
57 {
58 audit_syscall_entry(regs->orig_ax, regs->bx,
59 regs->cx, regs->dx, regs->si);
60 }
61}
62
63/*
64 * We can return 0 to resume the syscall or anything else to go to phase
65 * 2. If we resume the syscall, we need to put something appropriate in
66 * regs->orig_ax.
67 *
68 * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
69 * are fully functional.
70 *
71 * For phase 2's benefit, our return value is:
72 * 0: resume the syscall
73 * 1: go to phase 2; no seccomp phase 2 needed
74 * anything else: go to phase 2; pass return value to seccomp
75 */
76unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
77{
Andy Lutomirskidd636072015-10-05 17:48:22 -070078 struct thread_info *ti = pt_regs_to_thread_info(regs);
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070079 unsigned long ret = 0;
80 u32 work;
81
Andy Lutomirski4aabd142015-10-05 17:48:21 -070082 if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
83 BUG_ON(regs != task_pt_regs(current));
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070084
Andy Lutomirskidd636072015-10-05 17:48:22 -070085 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070086
Andy Lutomirskifeed36c2015-07-03 12:44:25 -070087#ifdef CONFIG_CONTEXT_TRACKING
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070088 /*
89 * If TIF_NOHZ is set, we are required to call user_exit() before
90 * doing anything that could touch RCU.
91 */
92 if (work & _TIF_NOHZ) {
Andy Lutomirskifeed36c2015-07-03 12:44:25 -070093 enter_from_user_mode();
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070094 work &= ~_TIF_NOHZ;
95 }
Andy Lutomirskifeed36c2015-07-03 12:44:25 -070096#endif
Andy Lutomirski1f484aa2015-07-03 12:44:23 -070097
98#ifdef CONFIG_SECCOMP
99 /*
100 * Do seccomp first -- it should minimize exposure of other
101 * code, and keeping seccomp fast is probably more valuable
102 * than the rest of this.
103 */
104 if (work & _TIF_SECCOMP) {
105 struct seccomp_data sd;
106
107 sd.arch = arch;
108 sd.nr = regs->orig_ax;
109 sd.instruction_pointer = regs->ip;
110#ifdef CONFIG_X86_64
111 if (arch == AUDIT_ARCH_X86_64) {
112 sd.args[0] = regs->di;
113 sd.args[1] = regs->si;
114 sd.args[2] = regs->dx;
115 sd.args[3] = regs->r10;
116 sd.args[4] = regs->r8;
117 sd.args[5] = regs->r9;
118 } else
119#endif
120 {
121 sd.args[0] = regs->bx;
122 sd.args[1] = regs->cx;
123 sd.args[2] = regs->dx;
124 sd.args[3] = regs->si;
125 sd.args[4] = regs->di;
126 sd.args[5] = regs->bp;
127 }
128
129 BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
130 BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);
131
132 ret = seccomp_phase1(&sd);
133 if (ret == SECCOMP_PHASE1_SKIP) {
134 regs->orig_ax = -1;
135 ret = 0;
136 } else if (ret != SECCOMP_PHASE1_OK) {
137 return ret; /* Go directly to phase 2 */
138 }
139
140 work &= ~_TIF_SECCOMP;
141 }
142#endif
143
144 /* Do our best to finish without phase 2. */
145 if (work == 0)
146 return ret; /* seccomp and/or nohz only (ret == 0 here) */
147
148#ifdef CONFIG_AUDITSYSCALL
149 if (work == _TIF_SYSCALL_AUDIT) {
150 /*
151 * If there is no more work to be done except auditing,
152 * then audit in phase 1. Phase 2 always audits, so, if
153 * we audit here, then we can't go on to phase 2.
154 */
155 do_audit_syscall_entry(regs, arch);
156 return 0;
157 }
158#endif
159
160 return 1; /* Something is enabled that we can't handle in phase 1 */
161}
162
163/* Returns the syscall nr to run (which should match regs->orig_ax). */
164long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
165 unsigned long phase1_result)
166{
Andy Lutomirskidd636072015-10-05 17:48:22 -0700167 struct thread_info *ti = pt_regs_to_thread_info(regs);
Andy Lutomirski1f484aa2015-07-03 12:44:23 -0700168 long ret = 0;
Andy Lutomirskidd636072015-10-05 17:48:22 -0700169 u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
Andy Lutomirski1f484aa2015-07-03 12:44:23 -0700170
Andy Lutomirski4aabd142015-10-05 17:48:21 -0700171 if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
172 BUG_ON(regs != task_pt_regs(current));
Andy Lutomirski1f484aa2015-07-03 12:44:23 -0700173
174 /*
175 * If we stepped into a sysenter/syscall insn, it trapped in
176 * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
177 * If user-mode had set TF itself, then it's still clear from
178 * do_debug() and we need to set it again to restore the user
179 * state. If we entered on the slow path, TF was already set.
180 */
181 if (work & _TIF_SINGLESTEP)
182 regs->flags |= X86_EFLAGS_TF;
183
184#ifdef CONFIG_SECCOMP
185 /*
186 * Call seccomp_phase2 before running the other hooks so that
187 * they can see any changes made by a seccomp tracer.
188 */
189 if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
190 /* seccomp failures shouldn't expose any additional code. */
191 return -1;
192 }
193#endif
194
195 if (unlikely(work & _TIF_SYSCALL_EMU))
196 ret = -1L;
197
198 if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
199 tracehook_report_syscall_entry(regs))
200 ret = -1L;
201
202 if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
203 trace_sys_enter(regs, regs->orig_ax);
204
205 do_audit_syscall_entry(regs, arch);
206
207 return ret ?: regs->orig_ax;
208}
209
210long syscall_trace_enter(struct pt_regs *regs)
211{
212 u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
213 unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);
214
215 if (phase1_result == 0)
216 return regs->orig_ax;
217 else
218 return syscall_trace_enter_phase2(regs, arch, phase1_result);
219}
220
Andy Lutomirski39b48e52015-10-05 17:48:23 -0700221#define EXIT_TO_USERMODE_LOOP_FLAGS \
222 (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
223 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
224
225static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700226{
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700227 /*
228 * In order to return to user mode, we need to have IRQs off with
229 * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
230 * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags
231 * can be set at any time on preemptable kernels if we have IRQs on,
232 * so we need to loop. Disabling preemption wouldn't help: doing the
233 * work to clear some of the flags can sleep.
234 */
235 while (true) {
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700236 /* We have work to do. */
237 local_irq_enable();
238
239 if (cached_flags & _TIF_NEED_RESCHED)
240 schedule();
241
242 if (cached_flags & _TIF_UPROBE)
243 uprobe_notify_resume(regs);
244
245 /* deal with pending signal delivery */
246 if (cached_flags & _TIF_SIGPENDING)
247 do_signal(regs);
248
249 if (cached_flags & _TIF_NOTIFY_RESUME) {
250 clear_thread_flag(TIF_NOTIFY_RESUME);
251 tracehook_notify_resume(regs);
252 }
253
254 if (cached_flags & _TIF_USER_RETURN_NOTIFY)
255 fire_user_return_notifiers();
256
257 /* Disable IRQs and retry */
258 local_irq_disable();
Andy Lutomirski39b48e52015-10-05 17:48:23 -0700259
260 cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
261
262 if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
263 break;
264
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700265 }
Andy Lutomirski39b48e52015-10-05 17:48:23 -0700266}
267
268/* Called with IRQs disabled. */
269__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
270{
271 u32 cached_flags;
272
273 if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
274 local_irq_disable();
275
276 lockdep_sys_exit();
277
278 cached_flags =
279 READ_ONCE(pt_regs_to_thread_info(regs)->flags);
280
281 if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
282 exit_to_usermode_loop(regs, cached_flags);
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700283
284 user_enter();
285}
286
Andy Lutomirskif5e6a972015-10-05 17:48:24 -0700287#define SYSCALL_EXIT_WORK_FLAGS \
288 (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
289 _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
290
291static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
292{
293 bool step;
294
295 audit_syscall_exit(regs);
296
297 if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
298 trace_sys_exit(regs, regs->ax);
299
300 /*
301 * If TIF_SYSCALL_EMU is set, we only get here because of
302 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
303 * We already reported this syscall instruction in
304 * syscall_trace_enter().
305 */
306 step = unlikely(
307 (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
308 == _TIF_SINGLESTEP);
309 if (step || cached_flags & _TIF_SYSCALL_TRACE)
310 tracehook_report_syscall_exit(regs, step);
311}
312
Andy Lutomirski1f484aa2015-07-03 12:44:23 -0700313/*
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700314 * Called with IRQs on and fully valid regs. Returns with IRQs off in a
315 * state such that we can immediately switch to user mode.
316 */
Andy Lutomirskif5e6a972015-10-05 17:48:24 -0700317__visible inline void syscall_return_slowpath(struct pt_regs *regs)
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700318{
319 struct thread_info *ti = pt_regs_to_thread_info(regs);
320 u32 cached_flags = READ_ONCE(ti->flags);
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700321
322 CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
323
Andy Lutomirski460d1242015-10-05 17:48:18 -0700324 if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
325 WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700326 local_irq_enable();
327
328 /*
329 * First do one-time work. If these work items are enabled, we
330 * want to run them exactly once per syscall exit with IRQs on.
331 */
Andy Lutomirskif5e6a972015-10-05 17:48:24 -0700332 if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
333 syscall_slow_exit_work(regs, cached_flags);
Andy Lutomirskic5c46f52015-07-03 12:44:26 -0700334
335#ifdef CONFIG_COMPAT
336 /*
337 * Compat syscalls set TS_COMPAT. Make sure we clear it before
338 * returning to user mode.
339 */
340 ti->status &= ~TS_COMPAT;
341#endif
342
343 local_irq_disable();
344 prepare_exit_to_usermode(regs);
345}
Andy Lutomirskibd2d3a32015-10-05 17:48:08 -0700346
347#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
348/*
Andy Lutomirski8b13c252015-10-05 17:48:17 -0700349 * Does a 32-bit syscall. Called with IRQs on and does all entry and
Andy Lutomirski33c521292015-10-05 17:48:19 -0700350 * exit work and returns with IRQs off. This function is extremely hot
351 * in workloads that use it, and it's usually called from
352 * do_fast_syscall_32, so forcibly inline it to improve performance.
Andy Lutomirskibd2d3a32015-10-05 17:48:08 -0700353 */
Andy Lutomirski657c1ee2015-10-16 15:42:54 -0700354#ifdef CONFIG_X86_32
355/* 32-bit kernels use a trap gate for INT80, and the asm code calls here. */
356__visible
357#else
358/* 64-bit kernels use do_syscall_32_irqs_off() instead. */
359static
360#endif
361__always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
Andy Lutomirskibd2d3a32015-10-05 17:48:08 -0700362{
363 struct thread_info *ti = pt_regs_to_thread_info(regs);
364 unsigned int nr = (unsigned int)regs->orig_ax;
365
366#ifdef CONFIG_IA32_EMULATION
367 ti->status |= TS_COMPAT;
368#endif
369
Andy Lutomirskibd2d3a32015-10-05 17:48:08 -0700370 if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
371 /*
372 * Subtlety here: if ptrace pokes something larger than
373 * 2^32-1 into orig_ax, this truncates it. This may or
374 * may not be necessary, but it matches the old asm
375 * behavior.
376 */
377 nr = syscall_trace_enter(regs);
378 }
379
Andy Lutomirski33c521292015-10-05 17:48:19 -0700380 if (likely(nr < IA32_NR_syscalls)) {
Andy Lutomirskibd2d3a32015-10-05 17:48:08 -0700381 /*
382 * It's possible that a 32-bit syscall implementation
383 * takes a 64-bit parameter but nonetheless assumes that
384 * the high bits are zero. Make sure we zero-extend all
385 * of the args.
386 */
387 regs->ax = ia32_sys_call_table[nr](
388 (unsigned int)regs->bx, (unsigned int)regs->cx,
389 (unsigned int)regs->dx, (unsigned int)regs->si,
390 (unsigned int)regs->di, (unsigned int)regs->bp);
391 }
392
393 syscall_return_slowpath(regs);
394}
Andy Lutomirski710246d2015-10-05 17:48:10 -0700395
Andy Lutomirski657c1ee2015-10-16 15:42:54 -0700396#ifdef CONFIG_X86_64
397/* Handles INT80 on 64-bit kernels */
398__visible void do_syscall_32_irqs_off(struct pt_regs *regs)
Andy Lutomirski8b13c252015-10-05 17:48:17 -0700399{
400 local_irq_enable();
401 do_syscall_32_irqs_on(regs);
402}
Andy Lutomirski657c1ee2015-10-16 15:42:54 -0700403#endif
Andy Lutomirski8b13c252015-10-05 17:48:17 -0700404
Andy Lutomirski5f310f72015-10-05 17:48:15 -0700405/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
Andy Lutomirski7841b402015-10-05 17:48:12 -0700406__visible long do_fast_syscall_32(struct pt_regs *regs)
Andy Lutomirski710246d2015-10-05 17:48:10 -0700407{
408 /*
409 * Called using the internal vDSO SYSENTER/SYSCALL32 calling
410 * convention. Adjust regs so it looks like we entered using int80.
411 */
412
413 unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
414 vdso_image_32.sym_int80_landing_pad;
415
416 /*
417 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
418 * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
419 * Fix it up.
420 */
421 regs->ip = landing_pad;
422
423 /*
424 * Fetch ECX from where the vDSO stashed it.
425 *
426 * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
427 */
428 local_irq_enable();
Andy Lutomirskic68ca672015-10-05 17:48:20 -0700429 if (
430#ifdef CONFIG_X86_64
431 /*
432 * Micro-optimization: the pointer we're following is explicitly
433 * 32 bits, so it can't be out of range.
434 */
435 __get_user(*(u32 *)&regs->cx,
436 (u32 __user __force *)(unsigned long)(u32)regs->sp)
437#else
438 get_user(*(u32 *)&regs->cx,
439 (u32 __user __force *)(unsigned long)(u32)regs->sp)
440#endif
441 ) {
442
Andy Lutomirski710246d2015-10-05 17:48:10 -0700443 /* User code screwed up. */
444 local_irq_disable();
445 regs->ax = -EFAULT;
446#ifdef CONFIG_CONTEXT_TRACKING
447 enter_from_user_mode();
448#endif
449 prepare_exit_to_usermode(regs);
Andy Lutomirski7841b402015-10-05 17:48:12 -0700450 return 0; /* Keep it simple: use IRET. */
Andy Lutomirski710246d2015-10-05 17:48:10 -0700451 }
Andy Lutomirski710246d2015-10-05 17:48:10 -0700452
453 /* Now this is just like a normal syscall. */
Andy Lutomirski8b13c252015-10-05 17:48:17 -0700454 do_syscall_32_irqs_on(regs);
Andy Lutomirski7841b402015-10-05 17:48:12 -0700455
456#ifdef CONFIG_X86_64
457 /*
458 * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
459 * SYSRETL is available on all 64-bit CPUs, so we don't need to
460 * bother with SYSEXIT.
461 *
462 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
463 * because the ECX fixup above will ensure that this is essentially
464 * never the case.
465 */
466 return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
467 regs->ip == landing_pad &&
468 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
469#else
Andy Lutomirski5f310f72015-10-05 17:48:15 -0700470 /*
471 * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
472 *
473 * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
474 * because the ECX fixup above will ensure that this is essentially
475 * never the case.
476 *
477 * We don't allow syscalls at all from VM86 mode, but we still
478 * need to check VM, because we might be returning from sys_vm86.
479 */
480 return static_cpu_has(X86_FEATURE_SEP) &&
481 regs->cs == __USER_CS && regs->ss == __USER_DS &&
482 regs->ip == landing_pad &&
483 (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
Andy Lutomirski7841b402015-10-05 17:48:12 -0700484#endif
Andy Lutomirski710246d2015-10-05 17:48:10 -0700485}
Andy Lutomirskibd2d3a32015-10-05 17:48:08 -0700486#endif