arch/powerpc/kernel/uprobes.c

   1 /*
   2  * User-space Probes (UProbes) for powerpc
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright IBM Corporation, 2007-2012
  19  *
  20  * Adapted from the x86 port by Ananth N Mavinakayanahalli <ananth@in.ibm.com>
  21  */
  22 #include <linux/kernel.h>
  23 #include <linux/sched.h>
  24 #include <linux/ptrace.h>
  25 #include <linux/uprobes.h>
  26 #include <linux/uaccess.h>
  27 #include <linux/kdebug.h>
  28
  29 #include <asm/sstep.h>
  30
  31 #define UPROBE_TRAP_NR  UINT_MAX
  32
  33 /**
  34  * arch_uprobe_analyze_insn
  35  * @mm: the probed address space.
  36  * @arch_uprobe: the probepoint information.
  37  * @addr: vaddr to probe.
  38  * Return 0 on success or a -ve number on error.
  39  */
  40 int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
  41                 struct mm_struct *mm, unsigned long addr)
  42 {
  43         if (addr & 0x03)
  44                 return -EINVAL;
  45
  46         /*
  47          * We currently don't support a uprobe on an already
  48          * existing breakpoint instruction underneath
  49          */
  50         if (is_trap(auprobe->ainsn))
  51                 return -ENOTSUPP;
  52         return 0;
  53 }
  54
  55 /*
  56  * arch_uprobe_pre_xol - prepare to execute out of line.
  57  * @auprobe: the probepoint information.
  58  * @regs: reflects the saved user state of current task.
  59  */
  60 int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
  61 {
  62         struct arch_uprobe_task *autask = &current->utask->autask;
  63
  64         autask->saved_trap_nr = current->thread.trap_nr;
  65         current->thread.trap_nr = UPROBE_TRAP_NR;
  66         regs->nip = current->utask->xol_vaddr;
  67
  68         user_enable_single_step(current);
  69         return 0;
  70 }
  71
  72 /**
  73  * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
  74  * @regs: Reflects the saved state of the task after it has hit a breakpoint
  75  * instruction.
  76  * Return the address of the breakpoint instruction.
  77  */
  78 unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
  79 {
  80         return instruction_pointer(regs);
  81 }
  82
  83 /*
  84  * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
  85  * then detect the case where a singlestepped instruction jumps back to its
  86  * own address. It is assumed that anything like do_page_fault/do_trap/etc
  87  * sets thread.trap_nr != UINT_MAX.
  88  *
  89  * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
  90  * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
  91  * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
  92  */
  93 bool arch_uprobe_xol_was_trapped(struct task_struct *t)
  94 {
  95         if (t->thread.trap_nr != UPROBE_TRAP_NR)
  96                 return true;
  97
  98         return false;
  99 }
 100
 101 /*
 102  * Called after single-stepping. To avoid the SMP problems that can
 103  * occur when we temporarily put back the original opcode to
 104  * single-step, we single-stepped a copy of the instruction.
 105  *
 106  * This function prepares to resume execution after the single-step.
 107  */
 108 int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 109 {
 110         struct uprobe_task *utask = current->utask;
 111
 112         WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
 113
 114         current->thread.trap_nr = utask->autask.saved_trap_nr;
 115
 116         /*
 117          * On powerpc, except for loads and stores, most instructions
 118          * including ones that alter code flow (branches, calls, returns)
 119          * are emulated in the kernel. We get here only if the emulation
 120          * support doesn't exist and have to fix-up the next instruction
 121          * to be executed.
 122          */
 123         regs->nip = utask->vaddr + MAX_UINSN_BYTES;
 124
 125         user_disable_single_step(current);
 126         return 0;
 127 }
 128
 129 /* callback routine for handling exceptions. */
 130 int arch_uprobe_exception_notify(struct notifier_block *self,
 131                                 unsigned long val, void *data)
 132 {
 133         struct die_args *args = data;
 134         struct pt_regs *regs = args->regs;
 135
 136         /* regs == NULL is a kernel bug */
 137         if (WARN_ON(!regs))
 138                 return NOTIFY_DONE;
 139
 140         /* We are only interested in userspace traps */
 141         if (!user_mode(regs))
 142                 return NOTIFY_DONE;
 143
 144         switch (val) {
 145         case DIE_BPT:
 146                 if (uprobe_pre_sstep_notifier(regs))
 147                         return NOTIFY_STOP;
 148                 break;
 149         case DIE_SSTEP:
 150                 if (uprobe_post_sstep_notifier(regs))
 151                         return NOTIFY_STOP;
 152         default:
 153                 break;
 154         }
 155         return NOTIFY_DONE;
 156 }
 157
 158 /*
 159  * This function gets called when XOL instruction either gets trapped or
 160  * the thread has a fatal signal, so reset the instruction pointer to its
 161  * probed address.
 162  */
 163 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 164 {
 165         struct uprobe_task *utask = current->utask;
 166
 167         current->thread.trap_nr = utask->autask.saved_trap_nr;
 168         instruction_pointer_set(regs, utask->vaddr);
 169
 170         user_disable_single_step(current);
 171 }
 172
 173 /*
 174  * See if the instruction can be emulated.
 175  * Returns true if instruction was emulated, false otherwise.
 176  */
 177 bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 178 {
 179         int ret;
 180
 181         /*
 182          * emulate_step() returns 1 if the insn was successfully emulated.
 183          * For all other cases, we need to single-step in hardware.
 184          */
 185         ret = emulate_step(regs, auprobe->ainsn);
 186         if (ret > 0)
 187                 return true;
 188
 189         return false;
 190 }