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1f484aa6 AL |
1 | /* |
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> | |
27 | ||
28 | #define CREATE_TRACE_POINTS | |
29 | #include <trace/events/syscalls.h> | |
30 | ||
feed36cd AL |
31 | #ifdef CONFIG_CONTEXT_TRACKING |
32 | /* Called on entry from user mode with IRQs off. */ | |
33 | __visible void enter_from_user_mode(void) | |
34 | { | |
35 | CT_WARN_ON(ct_state() != CONTEXT_USER); | |
36 | user_exit(); | |
37 | } | |
38 | #endif | |
39 | ||
1f484aa6 AL |
40 | static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) |
41 | { | |
42 | #ifdef CONFIG_X86_64 | |
43 | if (arch == AUDIT_ARCH_X86_64) { | |
44 | audit_syscall_entry(regs->orig_ax, regs->di, | |
45 | regs->si, regs->dx, regs->r10); | |
46 | } else | |
47 | #endif | |
48 | { | |
49 | audit_syscall_entry(regs->orig_ax, regs->bx, | |
50 | regs->cx, regs->dx, regs->si); | |
51 | } | |
52 | } | |
53 | ||
54 | /* | |
55 | * We can return 0 to resume the syscall or anything else to go to phase | |
56 | * 2. If we resume the syscall, we need to put something appropriate in | |
57 | * regs->orig_ax. | |
58 | * | |
59 | * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax | |
60 | * are fully functional. | |
61 | * | |
62 | * For phase 2's benefit, our return value is: | |
63 | * 0: resume the syscall | |
64 | * 1: go to phase 2; no seccomp phase 2 needed | |
65 | * anything else: go to phase 2; pass return value to seccomp | |
66 | */ | |
67 | unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch) | |
68 | { | |
69 | unsigned long ret = 0; | |
70 | u32 work; | |
71 | ||
72 | BUG_ON(regs != task_pt_regs(current)); | |
73 | ||
74 | work = ACCESS_ONCE(current_thread_info()->flags) & | |
75 | _TIF_WORK_SYSCALL_ENTRY; | |
76 | ||
feed36cd | 77 | #ifdef CONFIG_CONTEXT_TRACKING |
1f484aa6 AL |
78 | /* |
79 | * If TIF_NOHZ is set, we are required to call user_exit() before | |
80 | * doing anything that could touch RCU. | |
81 | */ | |
82 | if (work & _TIF_NOHZ) { | |
feed36cd | 83 | enter_from_user_mode(); |
1f484aa6 AL |
84 | work &= ~_TIF_NOHZ; |
85 | } | |
feed36cd | 86 | #endif |
1f484aa6 AL |
87 | |
88 | #ifdef CONFIG_SECCOMP | |
89 | /* | |
90 | * Do seccomp first -- it should minimize exposure of other | |
91 | * code, and keeping seccomp fast is probably more valuable | |
92 | * than the rest of this. | |
93 | */ | |
94 | if (work & _TIF_SECCOMP) { | |
95 | struct seccomp_data sd; | |
96 | ||
97 | sd.arch = arch; | |
98 | sd.nr = regs->orig_ax; | |
99 | sd.instruction_pointer = regs->ip; | |
100 | #ifdef CONFIG_X86_64 | |
101 | if (arch == AUDIT_ARCH_X86_64) { | |
102 | sd.args[0] = regs->di; | |
103 | sd.args[1] = regs->si; | |
104 | sd.args[2] = regs->dx; | |
105 | sd.args[3] = regs->r10; | |
106 | sd.args[4] = regs->r8; | |
107 | sd.args[5] = regs->r9; | |
108 | } else | |
109 | #endif | |
110 | { | |
111 | sd.args[0] = regs->bx; | |
112 | sd.args[1] = regs->cx; | |
113 | sd.args[2] = regs->dx; | |
114 | sd.args[3] = regs->si; | |
115 | sd.args[4] = regs->di; | |
116 | sd.args[5] = regs->bp; | |
117 | } | |
118 | ||
119 | BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0); | |
120 | BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1); | |
121 | ||
122 | ret = seccomp_phase1(&sd); | |
123 | if (ret == SECCOMP_PHASE1_SKIP) { | |
124 | regs->orig_ax = -1; | |
125 | ret = 0; | |
126 | } else if (ret != SECCOMP_PHASE1_OK) { | |
127 | return ret; /* Go directly to phase 2 */ | |
128 | } | |
129 | ||
130 | work &= ~_TIF_SECCOMP; | |
131 | } | |
132 | #endif | |
133 | ||
134 | /* Do our best to finish without phase 2. */ | |
135 | if (work == 0) | |
136 | return ret; /* seccomp and/or nohz only (ret == 0 here) */ | |
137 | ||
138 | #ifdef CONFIG_AUDITSYSCALL | |
139 | if (work == _TIF_SYSCALL_AUDIT) { | |
140 | /* | |
141 | * If there is no more work to be done except auditing, | |
142 | * then audit in phase 1. Phase 2 always audits, so, if | |
143 | * we audit here, then we can't go on to phase 2. | |
144 | */ | |
145 | do_audit_syscall_entry(regs, arch); | |
146 | return 0; | |
147 | } | |
148 | #endif | |
149 | ||
150 | return 1; /* Something is enabled that we can't handle in phase 1 */ | |
151 | } | |
152 | ||
153 | /* Returns the syscall nr to run (which should match regs->orig_ax). */ | |
154 | long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch, | |
155 | unsigned long phase1_result) | |
156 | { | |
157 | long ret = 0; | |
158 | u32 work = ACCESS_ONCE(current_thread_info()->flags) & | |
159 | _TIF_WORK_SYSCALL_ENTRY; | |
160 | ||
161 | BUG_ON(regs != task_pt_regs(current)); | |
162 | ||
163 | /* | |
164 | * If we stepped into a sysenter/syscall insn, it trapped in | |
165 | * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. | |
166 | * If user-mode had set TF itself, then it's still clear from | |
167 | * do_debug() and we need to set it again to restore the user | |
168 | * state. If we entered on the slow path, TF was already set. | |
169 | */ | |
170 | if (work & _TIF_SINGLESTEP) | |
171 | regs->flags |= X86_EFLAGS_TF; | |
172 | ||
173 | #ifdef CONFIG_SECCOMP | |
174 | /* | |
175 | * Call seccomp_phase2 before running the other hooks so that | |
176 | * they can see any changes made by a seccomp tracer. | |
177 | */ | |
178 | if (phase1_result > 1 && seccomp_phase2(phase1_result)) { | |
179 | /* seccomp failures shouldn't expose any additional code. */ | |
180 | return -1; | |
181 | } | |
182 | #endif | |
183 | ||
184 | if (unlikely(work & _TIF_SYSCALL_EMU)) | |
185 | ret = -1L; | |
186 | ||
187 | if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) && | |
188 | tracehook_report_syscall_entry(regs)) | |
189 | ret = -1L; | |
190 | ||
191 | if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT))) | |
192 | trace_sys_enter(regs, regs->orig_ax); | |
193 | ||
194 | do_audit_syscall_entry(regs, arch); | |
195 | ||
196 | return ret ?: regs->orig_ax; | |
197 | } | |
198 | ||
199 | long syscall_trace_enter(struct pt_regs *regs) | |
200 | { | |
201 | u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64; | |
202 | unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch); | |
203 | ||
204 | if (phase1_result == 0) | |
205 | return regs->orig_ax; | |
206 | else | |
207 | return syscall_trace_enter_phase2(regs, arch, phase1_result); | |
208 | } | |
209 | ||
c5c46f59 AL |
210 | static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs) |
211 | { | |
212 | unsigned long top_of_stack = | |
213 | (unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING; | |
214 | return (struct thread_info *)(top_of_stack - THREAD_SIZE); | |
215 | } | |
216 | ||
217 | /* Called with IRQs disabled. */ | |
218 | __visible void prepare_exit_to_usermode(struct pt_regs *regs) | |
219 | { | |
220 | if (WARN_ON(!irqs_disabled())) | |
221 | local_irq_disable(); | |
222 | ||
223 | /* | |
224 | * In order to return to user mode, we need to have IRQs off with | |
225 | * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY, | |
226 | * _TIF_UPROBE, or _TIF_NEED_RESCHED set. Several of these flags | |
227 | * can be set at any time on preemptable kernels if we have IRQs on, | |
228 | * so we need to loop. Disabling preemption wouldn't help: doing the | |
229 | * work to clear some of the flags can sleep. | |
230 | */ | |
231 | while (true) { | |
232 | u32 cached_flags = | |
233 | READ_ONCE(pt_regs_to_thread_info(regs)->flags); | |
234 | ||
235 | if (!(cached_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | | |
d132803e AL |
236 | _TIF_UPROBE | _TIF_NEED_RESCHED | |
237 | _TIF_USER_RETURN_NOTIFY))) | |
c5c46f59 AL |
238 | break; |
239 | ||
240 | /* We have work to do. */ | |
241 | local_irq_enable(); | |
242 | ||
243 | if (cached_flags & _TIF_NEED_RESCHED) | |
244 | schedule(); | |
245 | ||
246 | if (cached_flags & _TIF_UPROBE) | |
247 | uprobe_notify_resume(regs); | |
248 | ||
249 | /* deal with pending signal delivery */ | |
250 | if (cached_flags & _TIF_SIGPENDING) | |
251 | do_signal(regs); | |
252 | ||
253 | if (cached_flags & _TIF_NOTIFY_RESUME) { | |
254 | clear_thread_flag(TIF_NOTIFY_RESUME); | |
255 | tracehook_notify_resume(regs); | |
256 | } | |
257 | ||
258 | if (cached_flags & _TIF_USER_RETURN_NOTIFY) | |
259 | fire_user_return_notifiers(); | |
260 | ||
261 | /* Disable IRQs and retry */ | |
262 | local_irq_disable(); | |
263 | } | |
264 | ||
265 | user_enter(); | |
266 | } | |
267 | ||
268 | /* | |
269 | * Called with IRQs on and fully valid regs. Returns with IRQs off in a | |
270 | * state such that we can immediately switch to user mode. | |
271 | */ | |
272 | __visible void syscall_return_slowpath(struct pt_regs *regs) | |
273 | { | |
274 | struct thread_info *ti = pt_regs_to_thread_info(regs); | |
275 | u32 cached_flags = READ_ONCE(ti->flags); | |
276 | bool step; | |
277 | ||
278 | CT_WARN_ON(ct_state() != CONTEXT_KERNEL); | |
279 | ||
280 | if (WARN(irqs_disabled(), "syscall %ld left IRQs disabled", | |
281 | regs->orig_ax)) | |
282 | local_irq_enable(); | |
283 | ||
284 | /* | |
285 | * First do one-time work. If these work items are enabled, we | |
286 | * want to run them exactly once per syscall exit with IRQs on. | |
287 | */ | |
288 | if (cached_flags & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | | |
289 | _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)) { | |
290 | audit_syscall_exit(regs); | |
291 | ||
292 | if (cached_flags & _TIF_SYSCALL_TRACEPOINT) | |
293 | trace_sys_exit(regs, regs->ax); | |
294 | ||
295 | /* | |
296 | * If TIF_SYSCALL_EMU is set, we only get here because of | |
297 | * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). | |
298 | * We already reported this syscall instruction in | |
299 | * syscall_trace_enter(). | |
300 | */ | |
301 | step = unlikely( | |
302 | (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) | |
303 | == _TIF_SINGLESTEP); | |
304 | if (step || cached_flags & _TIF_SYSCALL_TRACE) | |
305 | tracehook_report_syscall_exit(regs, step); | |
306 | } | |
307 | ||
308 | #ifdef CONFIG_COMPAT | |
309 | /* | |
310 | * Compat syscalls set TS_COMPAT. Make sure we clear it before | |
311 | * returning to user mode. | |
312 | */ | |
313 | ti->status &= ~TS_COMPAT; | |
314 | #endif | |
315 | ||
316 | local_irq_disable(); | |
317 | prepare_exit_to_usermode(regs); | |
318 | } |