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Linux/arch/arc/kernel/signal.c

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  1 /*
  2  * Signal Handling for ARC
  3  *
  4  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
  5  *
  6  * This program is free software; you can redistribute it and/or modify
  7  * it under the terms of the GNU General Public License version 2 as
  8  * published by the Free Software Foundation.
  9  *
 10  * vineetg: Jan 2010 (Restarting of timer related syscalls)
 11  *
 12  * vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK)
 13  *  -do_signal() supports TIF_RESTORE_SIGMASK
 14  *  -do_signal() no loner needs oldset, required by OLD sys_sigsuspend
 15  *  -sys_rt_sigsuspend() now comes from generic code, so discard arch implemen
 16  *  -sys_sigsuspend() no longer needs to fudge ptregs, hence that arg removed
 17  *  -sys_sigsuspend() no longer loops for do_signal(), sets TIF_xxx and leaves
 18  *   the job to do_signal()
 19  *
 20  * vineetg: July 2009
 21  *  -Modified Code to support the uClibc provided userland sigreturn stub
 22  *   to avoid kernel synthesing it on user stack at runtime, costing TLB
 23  *   probes and Cache line flushes.
 24  *
 25  * vineetg: July 2009
 26  *  -In stash_usr_regs( ) and restore_usr_regs( ), save/restore of user regs
 27  *   in done in block copy rather than one word at a time.
 28  *   This saves around 2K of code and improves LMBench lat_sig <catch>
 29  *
 30  * rajeshwarr: Feb 2009
 31  *  - Support for Realtime Signals
 32  *
 33  * vineetg: Aug 11th 2008: Bug #94183
 34  *  -ViXS were still seeing crashes when using insmod to load drivers.
 35  *   It turned out that the code to change Execute permssions for TLB entries
 36  *   of user was not guarded for interrupts (mod_tlb_permission)
 37  *   This was cauing TLB entries to be overwritten on unrelated indexes
 38  *
 39  * Vineetg: July 15th 2008: Bug #94183
 40  *  -Exception happens in Delay slot of a JMP, and before user space resumes,
 41  *   Signal is delivered (Ctrl + C) = >SIGINT.
 42  *   setup_frame( ) sets up PC,SP,BLINK to enable user space signal handler
 43  *   to run, but doesn't clear the Delay slot bit from status32. As a result,
 44  *   on resuming user mode, signal handler branches off to BTA of orig JMP
 45  *  -FIX: clear the DE bit from status32 in setup_frame( )
 46  *
 47  * Rahul Trivedi, Kanika Nema: Codito Technologies 2004
 48  */
 49 
 50 #include <linux/signal.h>
 51 #include <linux/ptrace.h>
 52 #include <linux/personality.h>
 53 #include <linux/uaccess.h>
 54 #include <linux/syscalls.h>
 55 #include <linux/tracehook.h>
 56 #include <asm/ucontext.h>
 57 
 58 struct rt_sigframe {
 59         struct siginfo info;
 60         struct ucontext uc;
 61 #define MAGIC_SIGALTSTK         0x07302004
 62         unsigned int sigret_magic;
 63 };
 64 
 65 static int
 66 stash_usr_regs(struct rt_sigframe __user *sf, struct pt_regs *regs,
 67                sigset_t *set)
 68 {
 69         int err;
 70         err = __copy_to_user(&(sf->uc.uc_mcontext.regs.scratch), regs,
 71                              sizeof(sf->uc.uc_mcontext.regs.scratch));
 72         err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(sigset_t));
 73 
 74         return err;
 75 }
 76 
 77 static int restore_usr_regs(struct pt_regs *regs, struct rt_sigframe __user *sf)
 78 {
 79         sigset_t set;
 80         int err;
 81 
 82         err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
 83         if (!err)
 84                 set_current_blocked(&set);
 85 
 86         err |= __copy_from_user(regs, &(sf->uc.uc_mcontext.regs.scratch),
 87                                 sizeof(sf->uc.uc_mcontext.regs.scratch));
 88 
 89         return err;
 90 }
 91 
 92 static inline int is_do_ss_needed(unsigned int magic)
 93 {
 94         if (MAGIC_SIGALTSTK == magic)
 95                 return 1;
 96         else
 97                 return 0;
 98 }
 99 
100 SYSCALL_DEFINE0(rt_sigreturn)
101 {
102         struct rt_sigframe __user *sf;
103         unsigned int magic;
104         struct pt_regs *regs = current_pt_regs();
105 
106         /* Always make any pending restarted system calls return -EINTR */
107         current->restart_block.fn = do_no_restart_syscall;
108 
109         /* Since we stacked the signal on a word boundary,
110          * then 'sp' should be word aligned here.  If it's
111          * not, then the user is trying to mess with us.
112          */
113         if (regs->sp & 3)
114                 goto badframe;
115 
116         sf = (struct rt_sigframe __force __user *)(regs->sp);
117 
118         if (!access_ok(VERIFY_READ, sf, sizeof(*sf)))
119                 goto badframe;
120 
121         if (__get_user(magic, &sf->sigret_magic))
122                 goto badframe;
123 
124         if (unlikely(is_do_ss_needed(magic)))
125                 if (restore_altstack(&sf->uc.uc_stack))
126                         goto badframe;
127 
128         if (restore_usr_regs(regs, sf))
129                 goto badframe;
130 
131         /* Don't restart from sigreturn */
132         syscall_wont_restart(regs);
133 
134         /*
135          * Ensure that sigreturn always returns to user mode (in case the
136          * regs saved on user stack got fudged between save and sigreturn)
137          * Otherwise it is easy to panic the kernel with a custom
138          * signal handler and/or restorer which clobberes the status32/ret
139          * to return to a bogus location in kernel mode.
140          */
141         regs->status32 |= STATUS_U_MASK;
142 
143         return regs->r0;
144 
145 badframe:
146         force_sig(SIGSEGV, current);
147         return 0;
148 }
149 
150 /*
151  * Determine which stack to use..
152  */
153 static inline void __user *get_sigframe(struct ksignal *ksig,
154                                         struct pt_regs *regs,
155                                         unsigned long framesize)
156 {
157         unsigned long sp = sigsp(regs->sp, ksig);
158         void __user *frame;
159 
160         /* No matter what happens, 'sp' must be word
161          * aligned otherwise nasty things could happen
162          */
163 
164         /* ATPCS B01 mandates 8-byte alignment */
165         frame = (void __user *)((sp - framesize) & ~7);
166 
167         /* Check that we can actually write to the signal frame */
168         if (!access_ok(VERIFY_WRITE, frame, framesize))
169                 frame = NULL;
170 
171         return frame;
172 }
173 
174 static int
175 setup_rt_frame(struct ksignal *ksig, sigset_t *set, struct pt_regs *regs)
176 {
177         struct rt_sigframe __user *sf;
178         unsigned int magic = 0;
179         int err = 0;
180 
181         sf = get_sigframe(ksig, regs, sizeof(struct rt_sigframe));
182         if (!sf)
183                 return 1;
184 
185         /*
186          * w/o SA_SIGINFO, struct ucontext is partially populated (only
187          * uc_mcontext/uc_sigmask) for kernel's normal user state preservation
188          * during signal handler execution. This works for SA_SIGINFO as well
189          * although the semantics are now overloaded (the same reg state can be
190          * inspected by userland: but are they allowed to fiddle with it ?
191          */
192         err |= stash_usr_regs(sf, regs, set);
193 
194         /*
195          * SA_SIGINFO requires 3 args to signal handler:
196          *  #1: sig-no (common to any handler)
197          *  #2: struct siginfo
198          *  #3: struct ucontext (completely populated)
199          */
200         if (unlikely(ksig->ka.sa.sa_flags & SA_SIGINFO)) {
201                 err |= copy_siginfo_to_user(&sf->info, &ksig->info);
202                 err |= __put_user(0, &sf->uc.uc_flags);
203                 err |= __put_user(NULL, &sf->uc.uc_link);
204                 err |= __save_altstack(&sf->uc.uc_stack, regs->sp);
205 
206                 /* setup args 2 and 3 for user mode handler */
207                 regs->r1 = (unsigned long)&sf->info;
208                 regs->r2 = (unsigned long)&sf->uc;
209 
210                 /*
211                  * small optim to avoid unconditonally calling do_sigaltstack
212                  * in sigreturn path, now that we only have rt_sigreturn
213                  */
214                 magic = MAGIC_SIGALTSTK;
215         }
216 
217         err |= __put_user(magic, &sf->sigret_magic);
218         if (err)
219                 return err;
220 
221         /* #1 arg to the user Signal handler */
222         regs->r0 = ksig->sig;
223 
224         /* setup PC of user space signal handler */
225         regs->ret = (unsigned long)ksig->ka.sa.sa_handler;
226 
227         /*
228          * handler returns using sigreturn stub provided already by userpsace
229          * If not, nuke the process right away
230          */
231         if(!(ksig->ka.sa.sa_flags & SA_RESTORER))
232                 return 1;
233 
234         regs->blink = (unsigned long)ksig->ka.sa.sa_restorer;
235 
236         /* User Stack for signal handler will be above the frame just carved */
237         regs->sp = (unsigned long)sf;
238 
239         /*
240          * Bug 94183, Clear the DE bit, so that when signal handler
241          * starts to run, it doesn't use BTA
242          */
243         regs->status32 &= ~STATUS_DE_MASK;
244         regs->status32 |= STATUS_L_MASK;
245 
246         return err;
247 }
248 
249 static void arc_restart_syscall(struct k_sigaction *ka, struct pt_regs *regs)
250 {
251         switch (regs->r0) {
252         case -ERESTART_RESTARTBLOCK:
253         case -ERESTARTNOHAND:
254                 /*
255                  * ERESTARTNOHAND means that the syscall should
256                  * only be restarted if there was no handler for
257                  * the signal, and since we only get here if there
258                  * is a handler, we don't restart
259                  */
260                 regs->r0 = -EINTR;   /* ERESTART_xxx is internal */
261                 break;
262 
263         case -ERESTARTSYS:
264                 /*
265                  * ERESTARTSYS means to restart the syscall if
266                  * there is no handler or the handler was
267                  * registered with SA_RESTART
268                  */
269                 if (!(ka->sa.sa_flags & SA_RESTART)) {
270                         regs->r0 = -EINTR;
271                         break;
272                 }
273                 /* fallthrough */
274 
275         case -ERESTARTNOINTR:
276                 /*
277                  * ERESTARTNOINTR means that the syscall should
278                  * be called again after the signal handler returns.
279                  * Setup reg state just as it was before doing the trap
280                  * r0 has been clobbered with sys call ret code thus it
281                  * needs to be reloaded with orig first arg to syscall
282                  * in orig_r0. Rest of relevant reg-file:
283                  * r8 (syscall num) and (r1 - r7) will be reset to
284                  * their orig user space value when we ret from kernel
285                  */
286                 regs->r0 = regs->orig_r0;
287                 regs->ret -= 4;
288                 break;
289         }
290 }
291 
292 /*
293  * OK, we're invoking a handler
294  */
295 static void
296 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
297 {
298         sigset_t *oldset = sigmask_to_save();
299         int failed;
300 
301         /* Set up the stack frame */
302         failed = setup_rt_frame(ksig, oldset, regs);
303 
304         signal_setup_done(failed, ksig, 0);
305 }
306 
307 void do_signal(struct pt_regs *regs)
308 {
309         struct ksignal ksig;
310         int restart_scall;
311 
312         restart_scall = in_syscall(regs) && syscall_restartable(regs);
313 
314         if (get_signal(&ksig)) {
315                 if (restart_scall) {
316                         arc_restart_syscall(&ksig.ka, regs);
317                         syscall_wont_restart(regs);     /* No more restarts */
318                 }
319                 handle_signal(&ksig, regs);
320                 return;
321         }
322 
323         if (restart_scall) {
324                 /* No handler for syscall: restart it */
325                 if (regs->r0 == -ERESTARTNOHAND ||
326                     regs->r0 == -ERESTARTSYS || regs->r0 == -ERESTARTNOINTR) {
327                         regs->r0 = regs->orig_r0;
328                         regs->ret -= 4;
329                 } else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
330                         regs->r8 = __NR_restart_syscall;
331                         regs->ret -= 4;
332                 }
333                 syscall_wont_restart(regs);     /* No more restarts */
334         }
335 
336         /* If there's no signal to deliver, restore the saved sigmask back */
337         restore_saved_sigmask();
338 }
339 
340 void do_notify_resume(struct pt_regs *regs)
341 {
342         /*
343          * ASM glue gaurantees that this is only called when returning to
344          * user mode
345          */
346         if (test_and_clear_thread_flag(TIF_NOTIFY_RESUME))
347                 tracehook_notify_resume(regs);
348 }
349 

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