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 #include <asm/inst.h>
  18
  19 #define UPROBE_TRAP_NR  UINT_MAX
  20
  21 /**
  22  * is_trap_insn - check if the instruction is a trap variant
  23  * @insn: instruction to be checked.
  24  * Returns true if @insn is a trap variant.
  25  */
  26 bool is_trap_insn(uprobe_opcode_t *insn)
  27 {
  28         return (is_trap(*insn));
  29 }
  30
  31 /**
  32  * arch_uprobe_analyze_insn
  33  * @mm: the probed address space.
  34  * @arch_uprobe: the probepoint information.
  35  * @addr: vaddr to probe.
  36  * Return 0 on success or a -ve number on error.
  37  */
  38 int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
  39                 struct mm_struct *mm, unsigned long addr)
  40 {
  41         if (addr & 0x03)
  42                 return -EINVAL;
  43
  44         if (cpu_has_feature(CPU_FTR_ARCH_31) &&
  45             ppc_inst_prefixed(ppc_inst_read(auprobe->insn)) &&
  46             (addr & 0x3f) == 60) {
  47                 pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n");
  48                 return -EINVAL;
  49         }
  50
  51         if (!can_single_step(ppc_inst_val(ppc_inst_read(auprobe->insn)))) {
  52                 pr_info_ratelimited("Cannot register a uprobe on instructions that can't be single stepped\n");
  53                 return -ENOTSUPP;
  54         }
  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_set_return_ip(regs, 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_set_return_ip(regs, (unsigned long)ppc_inst_next((void *)utask->vaddr, auprobe->insn));
 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                 break;
 157         default:
 158                 break;
 159         }
 160         return NOTIFY_DONE;
 161 }
 162
 163 /*
 164  * This function gets called when XOL instruction either gets trapped or
 165  * the thread has a fatal signal, so reset the instruction pointer to its
 166  * probed address.
 167  */
 168 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 169 {
 170         struct uprobe_task *utask = current->utask;
 171
 172         current->thread.trap_nr = utask->autask.saved_trap_nr;
 173         instruction_pointer_set(regs, utask->vaddr);
 174
 175         user_disable_single_step(current);
 176 }
 177
 178 /*
 179  * See if the instruction can be emulated.
 180  * Returns true if instruction was emulated, false otherwise.
 181  */
 182 bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 183 {
 184         int ret;
 185
 186         /*
 187          * emulate_step() returns 1 if the insn was successfully emulated.
 188          * For all other cases, we need to single-step in hardware.
 189          */
 190         ret = emulate_step(regs, ppc_inst_read(auprobe->insn));
 191         if (ret > 0)
 192                 return true;
 193
 194         return false;
 195 }
 196
 197 unsigned long
 198 arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
 199 {
 200         unsigned long orig_ret_vaddr;
 201
 202         orig_ret_vaddr = regs->link;
 203
 204         /* Replace the return addr with trampoline addr */
 205         regs->link = trampoline_vaddr;
 206
 207         return orig_ret_vaddr;
 208 }
 209
 210 bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
 211                                 struct pt_regs *regs)
 212 {
 213         if (ctx == RP_CHECK_CHAIN_CALL)
 214                 return regs->gpr[1] <= ret->stack;
 215         else
 216                 return regs->gpr[1] < ret->stack;
 217 }