signal.c

  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(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(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, &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(*fpstate, (void __user *)buf_fx, 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((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)) {
338		/* Whee! Actually deliver the signal.  */
339		handle_signal(&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 ", 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(arg, &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 */