1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (C) 1991, 1992 Linus Torvalds
4 * Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs
5 *
6 * 1997-11-28 Modified for POSIX.1b signals by Richard Henderson
7 * 2000-06-20 Pentium III FXSR, SSE support by Gareth Hughes
8 * 2000-2002 x86-64 support by Andi Kleen
9 */
10
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12
13 #include <linux/sched.h>
14 #include <linux/sched/task_stack.h>
15 #include <linux/mm.h>
16 #include <linux/smp.h>
17 #include <linux/kernel.h>
18 #include <linux/kstrtox.h>
19 #include <linux/errno.h>
20 #include <linux/wait.h>
21 #include <linux/unistd.h>
22 #include <linux/stddef.h>
23 #include <linux/personality.h>
24 #include <linux/uaccess.h>
25 #include <linux/user-return-notifier.h>
26 #include <linux/uprobes.h>
27 #include <linux/context_tracking.h>
28 #include <linux/entry-common.h>
29 #include <linux/syscalls.h>
30
31 #include <asm/processor.h>
32 #include <asm/ucontext.h>
33 #include <asm/fpu/signal.h>
34 #include <asm/fpu/xstate.h>
35 #include <asm/vdso.h>
36 #include <asm/mce.h>
37 #include <asm/sighandling.h>
38 #include <asm/vm86.h>
39
40 #include <asm/syscall.h>
41 #include <asm/sigframe.h>
42 #include <asm/signal.h>
43 #include <asm/shstk.h>
44
is_ia32_compat_frame(struct ksignal * ksig)45 static inline int is_ia32_compat_frame(struct ksignal *ksig)
46 {
47 return IS_ENABLED(CONFIG_IA32_EMULATION) &&
48 ksig->ka.sa.sa_flags & SA_IA32_ABI;
49 }
50
is_ia32_frame(struct ksignal * ksig)51 static inline int is_ia32_frame(struct ksignal *ksig)
52 {
53 return IS_ENABLED(CONFIG_X86_32) || is_ia32_compat_frame(ksig);
54 }
55
is_x32_frame(struct ksignal * ksig)56 static inline int is_x32_frame(struct ksignal *ksig)
57 {
58 return IS_ENABLED(CONFIG_X86_X32_ABI) &&
59 ksig->ka.sa.sa_flags & SA_X32_ABI;
60 }
61
62 /*
63 * Set up a signal frame.
64 */
65
66 /* x86 ABI requires 16-byte alignment */
67 #define FRAME_ALIGNMENT 16UL
68
69 #define MAX_FRAME_PADDING (FRAME_ALIGNMENT - 1)
70
71 /*
72 * Determine which stack to use..
73 */
74 void __user *
get_sigframe(struct ksignal * ksig,struct pt_regs * regs,size_t frame_size,void __user ** fpstate)75 get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
76 void __user **fpstate)
77 {
78 struct k_sigaction *ka = &ksig->ka;
79 int ia32_frame = is_ia32_frame(ksig);
80 /* Default to using normal stack */
81 bool nested_altstack = on_sig_stack(regs->sp);
82 bool entering_altstack = false;
83 unsigned long math_size = 0;
84 unsigned long sp = regs->sp;
85 unsigned long buf_fx = 0;
86
87 /* redzone */
88 if (!ia32_frame)
89 sp -= 128;
90
91 /* This is the X/Open sanctioned signal stack switching. */
92 if (ka->sa.sa_flags & SA_ONSTACK) {
93 /*
94 * This checks nested_altstack via sas_ss_flags(). Sensible
95 * programs use SS_AUTODISARM, which disables that check, and
96 * programs that don't use SS_AUTODISARM get compatible.
97 */
98 if (sas_ss_flags(sp) == 0) {
99 sp = current->sas_ss_sp + current->sas_ss_size;
100 entering_altstack = true;
101 }
102 } else if (ia32_frame &&
103 !nested_altstack &&
104 regs->ss != __USER_DS &&
105 !(ka->sa.sa_flags & SA_RESTORER) &&
106 ka->sa.sa_restorer) {
107 /* This is the legacy signal stack switching. */
108 sp = (unsigned long) ka->sa.sa_restorer;
109 entering_altstack = true;
110 }
111
112 sp = fpu__alloc_mathframe(sp, ia32_frame, &buf_fx, &math_size);
113 *fpstate = (void __user *)sp;
114
115 sp -= frame_size;
116
117 if (ia32_frame)
118 /*
119 * Align the stack pointer according to the i386 ABI,
120 * i.e. so that on function entry ((sp + 4) & 15) == 0.
121 */
122 sp = ((sp + 4) & -FRAME_ALIGNMENT) - 4;
123 else
124 sp = round_down(sp, FRAME_ALIGNMENT) - 8;
125
126 /*
127 * If we are on the alternate signal stack and would overflow it, don't.
128 * Return an always-bogus address instead so we will die with SIGSEGV.
129 */
130 if (unlikely((nested_altstack || entering_altstack) &&
131 !__on_sig_stack(sp))) {
132
133 if (show_unhandled_signals && printk_ratelimit())
134 pr_info("%s[%d] overflowed sigaltstack\n",
135 current->comm, task_pid_nr(current));
136
137 return (void __user *)-1L;
138 }
139
140 /* save i387 and extended state */
141 if (!copy_fpstate_to_sigframe(*fpstate, (void __user *)buf_fx, math_size))
142 return (void __user *)-1L;
143
144 return (void __user *)sp;
145 }
146
147 /*
148 * There are four different struct types for signal frame: sigframe_ia32,
149 * rt_sigframe_ia32, rt_sigframe_x32, and rt_sigframe. Use the worst case
150 * -- the largest size. It means the size for 64-bit apps is a bit more
151 * than needed, but this keeps the code simple.
152 */
153 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
154 # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct sigframe_ia32)
155 #else
156 # define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct rt_sigframe)
157 #endif
158
159 /*
160 * The FP state frame contains an XSAVE buffer which must be 64-byte aligned.
161 * If a signal frame starts at an unaligned address, extra space is required.
162 * This is the max alignment padding, conservatively.
163 */
164 #define MAX_XSAVE_PADDING 63UL
165
166 /*
167 * The frame data is composed of the following areas and laid out as:
168 *
169 * -------------------------
170 * | alignment padding |
171 * -------------------------
172 * | (f)xsave frame |
173 * -------------------------
174 * | fsave header |
175 * -------------------------
176 * | alignment padding |
177 * -------------------------
178 * | siginfo + ucontext |
179 * -------------------------
180 */
181
182 /* max_frame_size tells userspace the worst case signal stack size. */
183 static unsigned long __ro_after_init max_frame_size;
184 static unsigned int __ro_after_init fpu_default_state_size;
185
init_sigframe_size(void)186 static int __init init_sigframe_size(void)
187 {
188 fpu_default_state_size = fpu__get_fpstate_size();
189
190 max_frame_size = MAX_FRAME_SIGINFO_UCTXT_SIZE + MAX_FRAME_PADDING;
191
192 max_frame_size += fpu_default_state_size + MAX_XSAVE_PADDING;
193
194 /* Userspace expects an aligned size. */
195 max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT);
196
197 pr_info("max sigframe size: %lu\n", max_frame_size);
198 return 0;
199 }
200 early_initcall(init_sigframe_size);
201
get_sigframe_size(void)202 unsigned long get_sigframe_size(void)
203 {
204 return max_frame_size;
205 }
206
207 static int
setup_rt_frame(struct ksignal * ksig,struct pt_regs * regs)208 setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
209 {
210 /* Perform fixup for the pre-signal frame. */
211 rseq_signal_deliver(ksig, regs);
212
213 /* Set up the stack frame */
214 if (is_ia32_frame(ksig)) {
215 if (ksig->ka.sa.sa_flags & SA_SIGINFO)
216 return ia32_setup_rt_frame(ksig, regs);
217 else
218 return ia32_setup_frame(ksig, regs);
219 } else if (is_x32_frame(ksig)) {
220 return x32_setup_rt_frame(ksig, regs);
221 } else {
222 return x64_setup_rt_frame(ksig, regs);
223 }
224 }
225
226 static void
handle_signal(struct ksignal * ksig,struct pt_regs * regs)227 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
228 {
229 bool stepping, failed;
230 struct fpu *fpu = ¤t->thread.fpu;
231
232 if (v8086_mode(regs))
233 save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL);
234
235 /* Are we from a system call? */
236 if (syscall_get_nr(current, regs) != -1) {
237 /* If so, check system call restarting.. */
238 switch (syscall_get_error(current, regs)) {
239 case -ERESTART_RESTARTBLOCK:
240 case -ERESTARTNOHAND:
241 regs->ax = -EINTR;
242 break;
243
244 case -ERESTARTSYS:
245 if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
246 regs->ax = -EINTR;
247 break;
248 }
249 fallthrough;
250 case -ERESTARTNOINTR:
251 regs->ax = regs->orig_ax;
252 regs->ip -= 2;
253 break;
254 }
255 }
256
257 /*
258 * If TF is set due to a debugger (TIF_FORCED_TF), clear TF now
259 * so that register information in the sigcontext is correct and
260 * then notify the tracer before entering the signal handler.
261 */
262 stepping = test_thread_flag(TIF_SINGLESTEP);
263 if (stepping)
264 user_disable_single_step(current);
265
266 failed = (setup_rt_frame(ksig, regs) < 0);
267 if (!failed) {
268 /*
269 * Clear the direction flag as per the ABI for function entry.
270 *
271 * Clear RF when entering the signal handler, because
272 * it might disable possible debug exception from the
273 * signal handler.
274 *
275 * Clear TF for the case when it wasn't set by debugger to
276 * avoid the recursive send_sigtrap() in SIGTRAP handler.
277 */
278 regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF);
279 /*
280 * Ensure the signal handler starts with the new fpu state.
281 */
282 fpu__clear_user_states(fpu);
283 }
284 signal_setup_done(failed, ksig, stepping);
285 }
286
get_nr_restart_syscall(const struct pt_regs * regs)287 static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
288 {
289 #ifdef CONFIG_IA32_EMULATION
290 if (current->restart_block.arch_data & TS_COMPAT)
291 return __NR_ia32_restart_syscall;
292 #endif
293 #ifdef CONFIG_X86_X32_ABI
294 return __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT);
295 #else
296 return __NR_restart_syscall;
297 #endif
298 }
299
300 /*
301 * Note that 'init' is a special process: it doesn't get signals it doesn't
302 * want to handle. Thus you cannot kill init even with a SIGKILL even by
303 * mistake.
304 */
arch_do_signal_or_restart(struct pt_regs * regs)305 void arch_do_signal_or_restart(struct pt_regs *regs)
306 {
307 struct ksignal ksig;
308
309 if (get_signal(&ksig)) {
310 /* Whee! Actually deliver the signal. */
311 handle_signal(&ksig, regs);
312 return;
313 }
314
315 /* Did we come from a system call? */
316 if (syscall_get_nr(current, regs) != -1) {
317 /* Restart the system call - no handlers present */
318 switch (syscall_get_error(current, regs)) {
319 case -ERESTARTNOHAND:
320 case -ERESTARTSYS:
321 case -ERESTARTNOINTR:
322 regs->ax = regs->orig_ax;
323 regs->ip -= 2;
324 break;
325
326 case -ERESTART_RESTARTBLOCK:
327 regs->ax = get_nr_restart_syscall(regs);
328 regs->ip -= 2;
329 break;
330 }
331 }
332
333 /*
334 * If there's no signal to deliver, we just put the saved sigmask
335 * back.
336 */
337 restore_saved_sigmask();
338 }
339
signal_fault(struct pt_regs * regs,void __user * frame,char * where)340 void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
341 {
342 struct task_struct *me = current;
343
344 if (show_unhandled_signals && printk_ratelimit()) {
345 printk("%s"
346 "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx",
347 task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG,
348 me->comm, me->pid, where, frame,
349 regs->ip, regs->sp, regs->orig_ax);
350 print_vma_addr(KERN_CONT " in ", regs->ip);
351 pr_cont("\n");
352 }
353
354 force_sig(SIGSEGV);
355 }
356
357 #ifdef CONFIG_DYNAMIC_SIGFRAME
358 #ifdef CONFIG_STRICT_SIGALTSTACK_SIZE
359 static bool strict_sigaltstack_size __ro_after_init = true;
360 #else
361 static bool strict_sigaltstack_size __ro_after_init = false;
362 #endif
363
strict_sas_size(char * arg)364 static int __init strict_sas_size(char *arg)
365 {
366 return kstrtobool(arg, &strict_sigaltstack_size) == 0;
367 }
368 __setup("strict_sas_size", strict_sas_size);
369
370 /*
371 * MINSIGSTKSZ is 2048 and can't be changed despite the fact that AVX512
372 * exceeds that size already. As such programs might never use the
373 * sigaltstack they just continued to work. While always checking against
374 * the real size would be correct, this might be considered a regression.
375 *
376 * Therefore avoid the sanity check, unless enforced by kernel
377 * configuration or command line option.
378 *
379 * When dynamic FPU features are supported, the check is also enforced when
380 * the task has permissions to use dynamic features. Tasks which have no
381 * permission are checked against the size of the non-dynamic feature set
382 * if strict checking is enabled. This avoids forcing all tasks on the
383 * system to allocate large sigaltstacks even if they are never going
384 * to use a dynamic feature. As this is serialized via sighand::siglock
385 * any permission request for a dynamic feature either happened already
386 * or will see the newly install sigaltstack size in the permission checks.
387 */
sigaltstack_size_valid(size_t ss_size)388 bool sigaltstack_size_valid(size_t ss_size)
389 {
390 unsigned long fsize = max_frame_size - fpu_default_state_size;
391 u64 mask;
392
393 lockdep_assert_held(¤t->sighand->siglock);
394
395 if (!fpu_state_size_dynamic() && !strict_sigaltstack_size)
396 return true;
397
398 fsize += current->group_leader->thread.fpu.perm.__user_state_size;
399 if (likely(ss_size > fsize))
400 return true;
401
402 if (strict_sigaltstack_size)
403 return ss_size > fsize;
404
405 mask = current->group_leader->thread.fpu.perm.__state_perm;
406 if (mask & XFEATURE_MASK_USER_DYNAMIC)
407 return ss_size > fsize;
408
409 return true;
410 }
411 #endif /* CONFIG_DYNAMIC_SIGFRAME */
412