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  * is_trap_insn - check if the instruction is a trap variant
  35  * @insn: instruction to be checked.
  36  * Returns true if @insn is a trap variant.
  37  */
  38 bool is_trap_insn(uprobe_opcode_t *insn)
  39 {
  40         return (is_trap(*insn));
  41 }
  42
  43 /**
  44  * arch_uprobe_analyze_insn
  45  * @mm: the probed address space.
  46  * @arch_uprobe: the probepoint information.
  47  * @addr: vaddr to probe.
  48  * Return 0 on success or a -ve number on error.
  49  */
  50 int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
  51                 struct mm_struct *mm, unsigned long addr)
  52 {
  53         if (addr & 0x03)
  54                 return -EINVAL;
  55
  56         return 0;
  57 }
  58
  59 /*
  60  * arch_uprobe_pre_xol - prepare to execute out of line.
  61  * @auprobe: the probepoint information.
  62  * @regs: reflects the saved user state of current task.
  63  */
  64 int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
  65 {
  66         struct arch_uprobe_task *autask = &current->utask->autask;
  67
  68         autask->saved_trap_nr = current->thread.trap_nr;
  69         current->thread.trap_nr = UPROBE_TRAP_NR;
  70         regs->nip = current->utask->xol_vaddr;
  71
  72         user_enable_single_step(current);
  73         return 0;
  74 }
  75
  76 /**
  77  * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
  78  * @regs: Reflects the saved state of the task after it has hit a breakpoint
  79  * instruction.
  80  * Return the address of the breakpoint instruction.
  81  */
  82 unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
  83 {
  84         return instruction_pointer(regs);
  85 }
  86
  87 /*
  88  * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
  89  * then detect the case where a singlestepped instruction jumps back to its
  90  * own address. It is assumed that anything like do_page_fault/do_trap/etc
  91  * sets thread.trap_nr != UINT_MAX.
  92  *
  93  * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
  94  * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
  95  * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
  96  */
  97 bool arch_uprobe_xol_was_trapped(struct task_struct *t)
  98 {
  99         if (t->thread.trap_nr != UPROBE_TRAP_NR)
 100                 return true;
 101
 102         return false;
 103 }
 104
 105 /*
 106  * Called after single-stepping. To avoid the SMP problems that can
 107  * occur when we temporarily put back the original opcode to
 108  * single-step, we single-stepped a copy of the instruction.
 109  *
 110  * This function prepares to resume execution after the single-step.
 111  */
 112 int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 113 {
 114         struct uprobe_task *utask = current->utask;
 115
 116         WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
 117
 118         current->thread.trap_nr = utask->autask.saved_trap_nr;
 119
 120         /*
 121          * On powerpc, except for loads and stores, most instructions
 122          * including ones that alter code flow (branches, calls, returns)
 123          * are emulated in the kernel. We get here only if the emulation
 124          * support doesn't exist and have to fix-up the next instruction
 125          * to be executed.
 126          */
 127         regs->nip = utask->vaddr + MAX_UINSN_BYTES;
 128
 129         user_disable_single_step(current);
 130         return 0;
 131 }
 132
 133 /* callback routine for handling exceptions. */
 134 int arch_uprobe_exception_notify(struct notifier_block *self,
 135                                 unsigned long val, void *data)
 136 {
 137         struct die_args *args = data;
 138         struct pt_regs *regs = args->regs;
 139
 140         /* regs == NULL is a kernel bug */
 141         if (WARN_ON(!regs))
 142                 return NOTIFY_DONE;
 143
 144         /* We are only interested in userspace traps */
 145         if (!user_mode(regs))
 146                 return NOTIFY_DONE;
 147
 148         switch (val) {
 149         case DIE_BPT:
 150                 if (uprobe_pre_sstep_notifier(regs))
 151                         return NOTIFY_STOP;
 152                 break;
 153         case DIE_SSTEP:
 154                 if (uprobe_post_sstep_notifier(regs))
 155                         return NOTIFY_STOP;
 156         default:
 157                 break;
 158         }
 159         return NOTIFY_DONE;
 160 }
 161
 162 /*
 163  * This function gets called when XOL instruction either gets trapped or
 164  * the thread has a fatal signal, so reset the instruction pointer to its
 165  * probed address.
 166  */
 167 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 168 {
 169         struct uprobe_task *utask = current->utask;
 170
 171         current->thread.trap_nr = utask->autask.saved_trap_nr;
 172         instruction_pointer_set(regs, utask->vaddr);
 173
 174         user_disable_single_step(current);
 175 }
 176
 177 /*
 178  * See if the instruction can be emulated.
 179  * Returns true if instruction was emulated, false otherwise.
 180  */
 181 bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 182 {
 183         int ret;
 184
 185         /*
 186          * emulate_step() returns 1 if the insn was successfully emulated.
 187          * For all other cases, we need to single-step in hardware.
 188          */
 189         ret = emulate_step(regs, auprobe->ainsn);
 190         if (ret > 0)
 191                 return true;
 192
 193         return false;
 194 }
 195
 196 unsigned long
 197 arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
 198 {
 199         unsigned long orig_ret_vaddr;
 200
 201         orig_ret_vaddr = regs->link;
 202
 203         /* Replace the return addr with trampoline addr */
 204         regs->link = trampoline_vaddr;
 205
 206         return orig_ret_vaddr;
 207 }