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#include <linux/rseq.h>
31
32#include <asm/processor.h>
33#include <asm/ucontext.h>
34#include <asm/fpu/signal.h>
35#include <asm/fpu/xstate.h>
36#include <asm/vdso.h>
37#include <asm/mce.h>
38#include <asm/sighandling.h>
39#include <asm/vm86.h>
40
41#include <asm/syscall.h>
42#include <asm/sigframe.h>
43#include <asm/signal.h>
44#include <asm/shstk.h>
45
46static inline int is_ia32_compat_frame(struct ksignal *ksig)
47{
48 return IS_ENABLED(CONFIG_IA32_EMULATION) &&
49 ksig->ka.sa.sa_flags & SA_IA32_ABI;
50}
51
52static inline int is_ia32_frame(struct ksignal *ksig)
53{
54 return IS_ENABLED(CONFIG_X86_32) || is_ia32_compat_frame(ksig);
55}
56
57static inline int is_x32_frame(struct ksignal *ksig)
58{
59 return IS_ENABLED(CONFIG_X86_X32_ABI) &&
60 ksig->ka.sa.sa_flags & SA_X32_ABI;
61}
62
63/*
64 * Enable all pkeys temporarily, so as to ensure that both the current
65 * execution stack as well as the alternate signal stack are writeable.
66 * The application can use any of the available pkeys to protect the
67 * alternate signal stack, and we don't know which one it is, so enable
68 * all. The PKRU register will be reset to init_pkru later in the flow,
69 * in fpu__clear_user_states(), and it is the application's responsibility
70 * to enable the appropriate pkey as the first step in the signal handler
71 * so that the handler does not segfault.
72 */
73static inline u32 sig_prepare_pkru(void)
74{
75 u32 orig_pkru = read_pkru();
76
77 write_pkru(pkru: 0);
78 return orig_pkru;
79}
80
81/*
82 * Set up a signal frame.
83 */
84
85/* x86 ABI requires 16-byte alignment */
86#define FRAME_ALIGNMENT 16UL
87
88#define MAX_FRAME_PADDING (FRAME_ALIGNMENT - 1)
89
90/*
91 * Determine which stack to use..
92 */
93void __user *
94get_sigframe(struct ksignal *ksig, struct pt_regs *regs, size_t frame_size,
95 void __user **fpstate)
96{
97 struct k_sigaction *ka = &ksig->ka;
98 int ia32_frame = is_ia32_frame(ksig);
99 /* Default to using normal stack */
100 bool nested_altstack = on_sig_stack(sp: regs->sp);
101 bool entering_altstack = false;
102 unsigned long math_size = 0;
103 unsigned long sp = regs->sp;
104 unsigned long buf_fx = 0;
105 u32 pkru;
106
107 /* redzone */
108 if (!ia32_frame)
109 sp -= 128;
110
111 /* This is the X/Open sanctioned signal stack switching. */
112 if (ka->sa.sa_flags & SA_ONSTACK) {
113 /*
114 * This checks nested_altstack via sas_ss_flags(). Sensible
115 * programs use SS_AUTODISARM, which disables that check, and
116 * programs that don't use SS_AUTODISARM get compatible.
117 */
118 if (sas_ss_flags(sp) == 0) {
119 sp = current->sas_ss_sp + current->sas_ss_size;
120 entering_altstack = true;
121 }
122 } else if (ia32_frame &&
123 !nested_altstack &&
124 regs->ss != __USER_DS &&
125 !(ka->sa.sa_flags & SA_RESTORER) &&
126 ka->sa.sa_restorer) {
127 /* This is the legacy signal stack switching. */
128 sp = (unsigned long) ka->sa.sa_restorer;
129 entering_altstack = true;
130 }
131
132 sp = fpu__alloc_mathframe(sp, ia32_frame, buf_fx: &buf_fx, size: &math_size);
133 *fpstate = (void __user *)sp;
134
135 sp -= frame_size;
136
137 if (ia32_frame)
138 /*
139 * Align the stack pointer according to the i386 ABI,
140 * i.e. so that on function entry ((sp + 4) & 15) == 0.
141 */
142 sp = ((sp + 4) & -FRAME_ALIGNMENT) - 4;
143 else
144 sp = round_down(sp, FRAME_ALIGNMENT) - 8;
145
146 /*
147 * If we are on the alternate signal stack and would overflow it, don't.
148 * Return an always-bogus address instead so we will die with SIGSEGV.
149 */
150 if (unlikely((nested_altstack || entering_altstack) &&
151 !__on_sig_stack(sp))) {
152
153 if (show_unhandled_signals && printk_ratelimit())
154 pr_info("%s[%d] overflowed sigaltstack\n",
155 current->comm, task_pid_nr(current));
156
157 return (void __user *)-1L;
158 }
159
160 /* Update PKRU to enable access to the alternate signal stack. */
161 pkru = sig_prepare_pkru();
162 /* save i387 and extended state */
163 if (!copy_fpstate_to_sigframe(buf: *fpstate, fp: (void __user *)buf_fx, size: math_size, pkru)) {
164 /*
165 * Restore PKRU to the original, user-defined value; disable
166 * extra pkeys enabled for the alternate signal stack, if any.
167 */
168 write_pkru(pkru);
169 return (void __user *)-1L;
170 }
171
172 return (void __user *)sp;
173}
174
175/*
176 * There are four different struct types for signal frame: sigframe_ia32,
177 * rt_sigframe_ia32, rt_sigframe_x32, and rt_sigframe. Use the worst case
178 * -- the largest size. It means the size for 64-bit apps is a bit more
179 * than needed, but this keeps the code simple.
180 */
181#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
182# define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct sigframe_ia32)
183#else
184# define MAX_FRAME_SIGINFO_UCTXT_SIZE sizeof(struct rt_sigframe)
185#endif
186
187/*
188 * The FP state frame contains an XSAVE buffer which must be 64-byte aligned.
189 * If a signal frame starts at an unaligned address, extra space is required.
190 * This is the max alignment padding, conservatively.
191 */
192#define MAX_XSAVE_PADDING 63UL
193
194/*
195 * The frame data is composed of the following areas and laid out as:
196 *
197 * -------------------------
198 * | alignment padding |
199 * -------------------------
200 * | (f)xsave frame |
201 * -------------------------
202 * | fsave header |
203 * -------------------------
204 * | alignment padding |
205 * -------------------------
206 * | siginfo + ucontext |
207 * -------------------------
208 */
209
210/* max_frame_size tells userspace the worst case signal stack size. */
211static unsigned long __ro_after_init max_frame_size;
212static unsigned int __ro_after_init fpu_default_state_size;
213
214static int __init init_sigframe_size(void)
215{
216 fpu_default_state_size = fpu__get_fpstate_size();
217
218 max_frame_size = MAX_FRAME_SIGINFO_UCTXT_SIZE + MAX_FRAME_PADDING;
219
220 max_frame_size += fpu_default_state_size + MAX_XSAVE_PADDING;
221
222 /* Userspace expects an aligned size. */
223 max_frame_size = round_up(max_frame_size, FRAME_ALIGNMENT);
224
225 pr_info("max sigframe size: %lu\n", max_frame_size);
226 return 0;
227}
228early_initcall(init_sigframe_size);
229
230unsigned long get_sigframe_size(void)
231{
232 return max_frame_size;
233}
234
235static int
236setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
237{
238 /* Perform fixup for the pre-signal frame. */
239 rseq_signal_deliver(ksig, regs);
240
241 /* Set up the stack frame */
242 if (is_ia32_frame(ksig)) {
243 if (ksig->ka.sa.sa_flags & SA_SIGINFO)
244 return ia32_setup_rt_frame(ksig, regs);
245 else
246 return ia32_setup_frame(ksig, regs);
247 } else if (is_x32_frame(ksig)) {
248 return x32_setup_rt_frame(ksig, regs);
249 } else {
250 return x64_setup_rt_frame(ksig, regs);
251 }
252}
253
254static void
255handle_signal(struct ksignal *ksig, struct pt_regs *regs)
256{
257 bool stepping, failed;
258 struct fpu *fpu = x86_task_fpu(current);
259
260 if (v8086_mode(regs))
261 save_v86_state(a: (struct kernel_vm86_regs *) regs, VM86_SIGNAL);
262
263 /* Are we from a system call? */
264 if (syscall_get_nr(current, regs) != -1) {
265 /* If so, check system call restarting.. */
266 switch (syscall_get_error(current, regs)) {
267 case -ERESTART_RESTARTBLOCK:
268 case -ERESTARTNOHAND:
269 regs->ax = -EINTR;
270 break;
271
272 case -ERESTARTSYS:
273 if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
274 regs->ax = -EINTR;
275 break;
276 }
277 fallthrough;
278 case -ERESTARTNOINTR:
279 regs->ax = regs->orig_ax;
280 regs->ip -= 2;
281 break;
282 }
283 }
284
285 /*
286 * If TF is set due to a debugger (TIF_FORCED_TF), clear TF now
287 * so that register information in the sigcontext is correct and
288 * then notify the tracer before entering the signal handler.
289 */
290 stepping = test_thread_flag(TIF_SINGLESTEP);
291 if (stepping)
292 user_disable_single_step(current);
293
294 failed = (setup_rt_frame(ksig, regs) < 0);
295 if (!failed) {
296 /*
297 * Clear the direction flag as per the ABI for function entry.
298 *
299 * Clear RF when entering the signal handler, because
300 * it might disable possible debug exception from the
301 * signal handler.
302 *
303 * Clear TF for the case when it wasn't set by debugger to
304 * avoid the recursive send_sigtrap() in SIGTRAP handler.
305 */
306 regs->flags &= ~(X86_EFLAGS_DF|X86_EFLAGS_RF|X86_EFLAGS_TF);
307 /*
308 * Ensure the signal handler starts with the new fpu state.
309 */
310 fpu__clear_user_states(fpu);
311 }
312 signal_setup_done(failed, ksig, stepping);
313}
314
315static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
316{
317#ifdef CONFIG_IA32_EMULATION
318 if (current->restart_block.arch_data & TS_COMPAT)
319 return __NR_ia32_restart_syscall;
320#endif
321#ifdef CONFIG_X86_X32_ABI
322 return __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT);
323#else
324 return __NR_restart_syscall;
325#endif
326}
327
328/*
329 * Note that 'init' is a special process: it doesn't get signals it doesn't
330 * want to handle. Thus you cannot kill init even with a SIGKILL even by
331 * mistake.
332 */
333void arch_do_signal_or_restart(struct pt_regs *regs)
334{
335 struct ksignal ksig;
336
337 if (get_signal(ksig: &ksig)) {
338 /* Whee! Actually deliver the signal. */
339 handle_signal(ksig: &ksig, regs);
340 return;
341 }
342
343 /* Did we come from a system call? */
344 if (syscall_get_nr(current, regs) != -1) {
345 /* Restart the system call - no handlers present */
346 switch (syscall_get_error(current, regs)) {
347 case -ERESTARTNOHAND:
348 case -ERESTARTSYS:
349 case -ERESTARTNOINTR:
350 regs->ax = regs->orig_ax;
351 regs->ip -= 2;
352 break;
353
354 case -ERESTART_RESTARTBLOCK:
355 regs->ax = get_nr_restart_syscall(regs);
356 regs->ip -= 2;
357 break;
358 }
359 }
360
361 /*
362 * If there's no signal to deliver, we just put the saved sigmask
363 * back.
364 */
365 restore_saved_sigmask();
366}
367
368void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
369{
370 struct task_struct *me = current;
371
372 if (show_unhandled_signals && printk_ratelimit()) {
373 printk("%s"
374 "%s[%d] bad frame in %s frame:%p ip:%lx sp:%lx orax:%lx",
375 task_pid_nr(current) > 1 ? KERN_INFO : KERN_EMERG,
376 me->comm, me->pid, where, frame,
377 regs->ip, regs->sp, regs->orig_ax);
378 print_vma_addr(KERN_CONT " in ", rip: regs->ip);
379 pr_cont("\n");
380 }
381
382 force_sig(SIGSEGV);
383}
384
385#ifdef CONFIG_DYNAMIC_SIGFRAME
386#ifdef CONFIG_STRICT_SIGALTSTACK_SIZE
387static bool strict_sigaltstack_size __ro_after_init = true;
388#else
389static bool strict_sigaltstack_size __ro_after_init = false;
390#endif
391
392static int __init strict_sas_size(char *arg)
393{
394 return kstrtobool(s: arg, res: &strict_sigaltstack_size) == 0;
395}
396__setup("strict_sas_size", strict_sas_size);
397
398/*
399 * MINSIGSTKSZ is 2048 and can't be changed despite the fact that AVX512
400 * exceeds that size already. As such programs might never use the
401 * sigaltstack they just continued to work. While always checking against
402 * the real size would be correct, this might be considered a regression.
403 *
404 * Therefore avoid the sanity check, unless enforced by kernel
405 * configuration or command line option.
406 *
407 * When dynamic FPU features are supported, the check is also enforced when
408 * the task has permissions to use dynamic features. Tasks which have no
409 * permission are checked against the size of the non-dynamic feature set
410 * if strict checking is enabled. This avoids forcing all tasks on the
411 * system to allocate large sigaltstacks even if they are never going
412 * to use a dynamic feature. As this is serialized via sighand::siglock
413 * any permission request for a dynamic feature either happened already
414 * or will see the newly install sigaltstack size in the permission checks.
415 */
416bool sigaltstack_size_valid(size_t ss_size)
417{
418 unsigned long fsize = max_frame_size - fpu_default_state_size;
419 u64 mask;
420
421 lockdep_assert_held(&current->sighand->siglock);
422
423 if (!fpu_state_size_dynamic() && !strict_sigaltstack_size)
424 return true;
425
426 fsize += x86_task_fpu(current->group_leader)->perm.__user_state_size;
427 if (likely(ss_size > fsize))
428 return true;
429
430 if (strict_sigaltstack_size)
431 return ss_size > fsize;
432
433 mask = x86_task_fpu(current->group_leader)->perm.__state_perm;
434 if (mask & XFEATURE_MASK_USER_DYNAMIC)
435 return ss_size > fsize;
436
437 return true;
438}
439#endif /* CONFIG_DYNAMIC_SIGFRAME */
440

source code of linux/arch/x86/kernel/signal.c