arch/powerpc/kernel/uprobes.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * User-space Probes (UProbes) for powerpc
   4  *
   5  * Copyright IBM Corporation, 2007-2012
   6  *
   7  * Adapted from the x86 port by Ananth N Mavinakayanahalli <ananth@in.ibm.com>
   8  */
   9 #include <linux/kernel.h>
  10 #include <linux/sched.h>
  11 #include <linux/ptrace.h>
  12 #include <linux/uprobes.h>
  13 #include <linux/uaccess.h>
  14 #include <linux/kdebug.h>
  15
  16 #include <asm/sstep.h>
  17
  18 #define UPROBE_TRAP_NR  UINT_MAX
  19
  20 /**
  21  * is_trap_insn - check if the instruction is a trap variant
  22  * @insn: instruction to be checked.
  23  * Returns true if @insn is a trap variant.
  24  */
  25 bool is_trap_insn(uprobe_opcode_t *insn)
  26 {
  27         return (is_trap(*insn));
  28 }
  29
  30 /**
  31  * arch_uprobe_analyze_insn
  32  * @mm: the probed address space.
  33  * @arch_uprobe: the probepoint information.
  34  * @addr: vaddr to probe.
  35  * Return 0 on success or a -ve number on error.
  36  */
  37 int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
  38                 struct mm_struct *mm, unsigned long addr)
  39 {
  40         if (addr & 0x03)
  41                 return -EINVAL;
  42
  43         return 0;
  44 }
  45
  46 /*
  47  * arch_uprobe_pre_xol - prepare to execute out of line.
  48  * @auprobe: the probepoint information.
  49  * @regs: reflects the saved user state of current task.
  50  */
  51 int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
  52 {
  53         struct arch_uprobe_task *autask = &current->utask->autask;
  54
  55         autask->saved_trap_nr = current->thread.trap_nr;
  56         current->thread.trap_nr = UPROBE_TRAP_NR;
  57         regs->nip = current->utask->xol_vaddr;
  58
  59         user_enable_single_step(current);
  60         return 0;
  61 }
  62
  63 /**
  64  * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
  65  * @regs: Reflects the saved state of the task after it has hit a breakpoint
  66  * instruction.
  67  * Return the address of the breakpoint instruction.
  68  */
  69 unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
  70 {
  71         return instruction_pointer(regs);
  72 }
  73
  74 /*
  75  * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
  76  * then detect the case where a singlestepped instruction jumps back to its
  77  * own address. It is assumed that anything like do_page_fault/do_trap/etc
  78  * sets thread.trap_nr != UINT_MAX.
  79  *
  80  * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
  81  * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
  82  * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
  83  */
  84 bool arch_uprobe_xol_was_trapped(struct task_struct *t)
  85 {
  86         if (t->thread.trap_nr != UPROBE_TRAP_NR)
  87                 return true;
  88
  89         return false;
  90 }
  91
  92 /*
  93  * Called after single-stepping. To avoid the SMP problems that can
  94  * occur when we temporarily put back the original opcode to
  95  * single-step, we single-stepped a copy of the instruction.
  96  *
  97  * This function prepares to resume execution after the single-step.
  98  */
  99 int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 100 {
 101         struct uprobe_task *utask = current->utask;
 102
 103         WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
 104
 105         current->thread.trap_nr = utask->autask.saved_trap_nr;
 106
 107         /*
 108          * On powerpc, except for loads and stores, most instructions
 109          * including ones that alter code flow (branches, calls, returns)
 110          * are emulated in the kernel. We get here only if the emulation
 111          * support doesn't exist and have to fix-up the next instruction
 112          * to be executed.
 113          */
 114         regs->nip = utask->vaddr + MAX_UINSN_BYTES;
 115
 116         user_disable_single_step(current);
 117         return 0;
 118 }
 119
 120 /* callback routine for handling exceptions. */
 121 int arch_uprobe_exception_notify(struct notifier_block *self,
 122                                 unsigned long val, void *data)
 123 {
 124         struct die_args *args = data;
 125         struct pt_regs *regs = args->regs;
 126
 127         /* regs == NULL is a kernel bug */
 128         if (WARN_ON(!regs))
 129                 return NOTIFY_DONE;
 130
 131         /* We are only interested in userspace traps */
 132         if (!user_mode(regs))
 133                 return NOTIFY_DONE;
 134
 135         switch (val) {
 136         case DIE_BPT:
 137                 if (uprobe_pre_sstep_notifier(regs))
 138                         return NOTIFY_STOP;
 139                 break;
 140         case DIE_SSTEP:
 141                 if (uprobe_post_sstep_notifier(regs))
 142                         return NOTIFY_STOP;
 143         default:
 144                 break;
 145         }
 146         return NOTIFY_DONE;
 147 }
 148
 149 /*
 150  * This function gets called when XOL instruction either gets trapped or
 151  * the thread has a fatal signal, so reset the instruction pointer to its
 152  * probed address.
 153  */
 154 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 155 {
 156         struct uprobe_task *utask = current->utask;
 157
 158         current->thread.trap_nr = utask->autask.saved_trap_nr;
 159         instruction_pointer_set(regs, utask->vaddr);
 160
 161         user_disable_single_step(current);
 162 }
 163
 164 /*
 165  * See if the instruction can be emulated.
 166  * Returns true if instruction was emulated, false otherwise.
 167  */
 168 bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 169 {
 170         int ret;
 171
 172         /*
 173          * emulate_step() returns 1 if the insn was successfully emulated.
 174          * For all other cases, we need to single-step in hardware.
 175          */
 176         ret = emulate_step(regs, auprobe->insn);
 177         if (ret > 0)
 178                 return true;
 179
 180         return false;
 181 }
 182
 183 unsigned long
 184 arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
 185 {
 186         unsigned long orig_ret_vaddr;
 187
 188         orig_ret_vaddr = regs->link;
 189
 190         /* Replace the return addr with trampoline addr */
 191         regs->link = trampoline_vaddr;
 192
 193         return orig_ret_vaddr;
 194 }
 195
 196 bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
 197                                 struct pt_regs *regs)
 198 {
 199         if (ctx == RP_CHECK_CHAIN_CALL)
 200                 return regs->gpr[1] <= ret->stack;
 201         else
 202                 return regs->gpr[1] < ret->stack;
 203 }