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 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  Kernel Probes (KProbes)
  *
  * Copyright (C) IBM Corporation, 2002, 2004
  *
  * 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  *      Probes initial implementation ( includes contributions from
  *      Rusty Russell).
  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  *      interface to access function arguments.
  * 2004-Nov Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  *      for PPC64
  */
 
 #include <linux/kprobes.h>
 #include <linux/ptrace.h>
 #include <linux/preempt.h>
 #include <linux/extable.h>
 #include <linux/kdebug.h>
 #include <linux/slab.h>
 #include <linux/moduleloader.h>
 #include <asm/code-patching.h>
 #include <asm/cacheflush.h>
 #include <asm/sstep.h>
 #include <asm/sections.h>
 #include <asm/inst.h>
 #include <asm/set_memory.h>
 #include <linux/uaccess.h>
 
 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 
 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
 
 bool arch_within_kprobe_blacklist(unsigned long addr)
 {
     return  (addr >= (unsigned long)__kprobes_text_start &&
          addr < (unsigned long)__kprobes_text_end) ||
         (addr >= (unsigned long)_stext &&
          addr < (unsigned long)__head_end);
 }
 
 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
 {
     kprobe_opcode_t *addr = NULL;
 
 #ifdef CONFIG_PPC64_ELF_ABI_V2
     /* PPC64 ABIv2 needs local entry point */
     addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
     if (addr && !offset) {
 #ifdef CONFIG_KPROBES_ON_FTRACE
         unsigned long faddr;
         /*
          * Per livepatch.h, ftrace location is always within the first
          * 16 bytes of a function on powerpc with -mprofile-kernel.
          */
         faddr = ftrace_location_range((unsigned long)addr,
                           (unsigned long)addr + 16);
         if (faddr)
             addr = (kprobe_opcode_t *)faddr;
         else
 #endif
             addr = (kprobe_opcode_t *)ppc_function_entry(addr);
     }
 #elif defined(CONFIG_PPC64_ELF_ABI_V1)
     /*
      * 64bit powerpc ABIv1 uses function descriptors:
      * - Check for the dot variant of the symbol first.
      * - If that fails, try looking up the symbol provided.
      *
      * This ensures we always get to the actual symbol and not
      * the descriptor.
      *
      * Also handle <module:symbol> format.
      */
     char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
     bool dot_appended = false;
     const char *c;
     ssize_t ret = 0;
     int len = 0;
 
     if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
         c++;
         len = c - name;
         memcpy(dot_name, name, len);
     } else
         c = name;
 
     if (*c != '\0' && *c != '.') {
         dot_name[len++] = '.';
         dot_appended = true;
     }
     ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
     if (ret > 0)
         addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
 
     /* Fallback to the original non-dot symbol lookup */
     if (!addr && dot_appended)
         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
 #else
     addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
 #endif
 
     return addr;
 }
 
 static bool arch_kprobe_on_func_entry(unsigned long offset)
 {
 #ifdef CONFIG_PPC64_ELF_ABI_V2
 #ifdef CONFIG_KPROBES_ON_FTRACE
     return offset <= 16;
 #else
     return offset <= 8;
 #endif
 #else
     return !offset;
 #endif
 }
 
 /* XXX try and fold the magic of kprobe_lookup_name() in this */
 kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
                      bool *on_func_entry)
 {
     *on_func_entry = arch_kprobe_on_func_entry(offset);
     return (kprobe_opcode_t *)(addr + offset);
 }
 
 void *alloc_insn_page(void)
 {
     void *page;
 
     page = module_alloc(PAGE_SIZE);
     if (!page)
         return NULL;
 
     if (strict_module_rwx_enabled()) {
         set_memory_ro((unsigned long)page, 1);
         set_memory_x((unsigned long)page, 1);
     }
     return page;
 }
 
 int arch_prepare_kprobe(struct kprobe *p)
 {
     int ret = 0;
     struct kprobe *prev;
     ppc_inst_t insn = ppc_inst_read(p->addr);
 
     if ((unsigned long)p->addr & 0x03) {
         printk("Attempt to register kprobe at an unaligned address\n");
         ret = -EINVAL;
     } else if (!can_single_step(ppc_inst_val(insn))) {
         printk("Cannot register a kprobe on instructions that can't be single stepped\n");
         ret = -EINVAL;
     } else if ((unsigned long)p->addr & ~PAGE_MASK &&
            ppc_inst_prefixed(ppc_inst_read(p->addr - 1))) {
         printk("Cannot register a kprobe on the second word of prefixed instruction\n");
         ret = -EINVAL;
     }
     preempt_disable();
     prev = get_kprobe(p->addr - 1);
     preempt_enable_no_resched();
     if (prev && ppc_inst_prefixed(ppc_inst_read(prev->ainsn.insn))) {
         printk("Cannot register a kprobe on the second word of prefixed instruction\n");
         ret = -EINVAL;
     }
 
     /* insn must be on a special executable page on ppc64.  This is
      * not explicitly required on ppc32 (right now), but it doesn't hurt */
     if (!ret) {
         p->ainsn.insn = get_insn_slot();
         if (!p->ainsn.insn)
             ret = -ENOMEM;
     }
 
     if (!ret) {
         patch_instruction(p->ainsn.insn, insn);
         p->opcode = ppc_inst_val(insn);
     }
 
     p->ainsn.boostable = 0;
     return ret;
 }
 NOKPROBE_SYMBOL(arch_prepare_kprobe);
 
 void arch_arm_kprobe(struct kprobe *p)
 {
     WARN_ON_ONCE(patch_instruction(p->addr, ppc_inst(BREAKPOINT_INSTRUCTION)));
 }
 NOKPROBE_SYMBOL(arch_arm_kprobe);
 
 void arch_disarm_kprobe(struct kprobe *p)
 {
     WARN_ON_ONCE(patch_instruction(p->addr, ppc_inst(p->opcode)));
 }
 NOKPROBE_SYMBOL(arch_disarm_kprobe);
 
 void arch_remove_kprobe(struct kprobe *p)
 {
     if (p->ainsn.insn) {
         free_insn_slot(p->ainsn.insn, 0);
         p->ainsn.insn = NULL;
     }
 }
 NOKPROBE_SYMBOL(arch_remove_kprobe);
 
 static nokprobe_inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
     enable_single_step(regs);
 
     /*
      * On powerpc we should single step on the original
      * instruction even if the probed insn is a trap
      * variant as values in regs could play a part in
      * if the trap is taken or not
      */
     regs_set_return_ip(regs, (unsigned long)p->ainsn.insn);
 }
 
 static nokprobe_inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
     kcb->prev_kprobe.kp = kprobe_running();
     kcb->prev_kprobe.status = kcb->kprobe_status;
     kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 }
 
 static nokprobe_inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
     __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
     kcb->kprobe_status = kcb->prev_kprobe.status;
     kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 }
 
 static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                 struct kprobe_ctlblk *kcb)
 {
     __this_cpu_write(current_kprobe, p);
     kcb->kprobe_saved_msr = regs->msr;
 }
 
 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
 {
     ri->ret_addr = (kprobe_opcode_t *)regs->link;
     ri->fp = NULL;
 
     /* Replace the return addr with trampoline addr */
     regs->link = (unsigned long)__kretprobe_trampoline;
 }
 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
 
 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
 {
     int ret;
     ppc_inst_t insn = ppc_inst_read(p->ainsn.insn);
 
     /* regs->nip is also adjusted if emulate_step returns 1 */
     ret = emulate_step(regs, insn);
     if (ret > 0) {
         /*
          * Once this instruction has been boosted
          * successfully, set the boostable flag
          */
         if (unlikely(p->ainsn.boostable == 0))
             p->ainsn.boostable = 1;
     } else if (ret < 0) {
         /*
          * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
          * So, we should never get here... but, its still
          * good to catch them, just in case...
          */
         printk("Can't step on instruction %08lx\n", ppc_inst_as_ulong(insn));
         BUG();
     } else {
         /*
          * If we haven't previously emulated this instruction, then it
          * can't be boosted. Note it down so we don't try to do so again.
          *
          * If, however, we had emulated this instruction in the past,
          * then this is just an error with the current run (for
          * instance, exceptions due to a load/store). We return 0 so
          * that this is now single-stepped, but continue to try
          * emulating it in subsequent probe hits.
          */
         if (unlikely(p->ainsn.boostable != 1))
             p->ainsn.boostable = -1;
     }
 
     return ret;
 }
 NOKPROBE_SYMBOL(try_to_emulate);
 
 int kprobe_handler(struct pt_regs *regs)
 {
     struct kprobe *p;
     int ret = 0;
     unsigned int *addr = (unsigned int *)regs->nip;
     struct kprobe_ctlblk *kcb;
 
     if (user_mode(regs))
         return 0;
 
     if (!IS_ENABLED(CONFIG_BOOKE) &&
         (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR)))
         return 0;
 
     /*
      * We don't want to be preempted for the entire
      * duration of kprobe processing
      */
     preempt_disable();
     kcb = get_kprobe_ctlblk();
 
     p = get_kprobe(addr);
     if (!p) {
         unsigned int instr;
 
         if (get_kernel_nofault(instr, addr))
             goto no_kprobe;
 
         if (instr != BREAKPOINT_INSTRUCTION) {
             /*
              * PowerPC has multiple variants of the "trap"
              * instruction. If the current instruction is a
              * trap variant, it could belong to someone else
              */
             if (is_trap(instr))
                 goto no_kprobe;
             /*
              * The breakpoint instruction was removed right
              * after we hit it.  Another cpu has removed
              * either a probepoint or a debugger breakpoint
              * at this address.  In either case, no further
              * handling of this interrupt is appropriate.
              */
             ret = 1;
         }
         /* Not one of ours: let kernel handle it */
         goto no_kprobe;
     }
 
     /* Check we're not actually recursing */
     if (kprobe_running()) {
         kprobe_opcode_t insn = *p->ainsn.insn;
         if (kcb->kprobe_status == KPROBE_HIT_SS && is_trap(insn)) {
             /* Turn off 'trace' bits */
             regs_set_return_msr(regs,
                 (regs->msr & ~MSR_SINGLESTEP) |
                 kcb->kprobe_saved_msr);
             goto no_kprobe;
         }
 
         /*
          * We have reentered the kprobe_handler(), since another probe
          * was hit while within the handler. We here save the original
          * kprobes variables and just single step on the instruction of
          * the new probe without calling any user handlers.
          */
         save_previous_kprobe(kcb);
         set_current_kprobe(p, regs, kcb);
         kprobes_inc_nmissed_count(p);
         kcb->kprobe_status = KPROBE_REENTER;
         if (p->ainsn.boostable >= 0) {
             ret = try_to_emulate(p, regs);
 
             if (ret > 0) {
                 restore_previous_kprobe(kcb);
                 preempt_enable_no_resched();
                 return 1;
             }
         }
         prepare_singlestep(p, regs);
         return 1;
     }
 
     kcb->kprobe_status = KPROBE_HIT_ACTIVE;
     set_current_kprobe(p, regs, kcb);
     if (p->pre_handler && p->pre_handler(p, regs)) {
         /* handler changed execution path, so skip ss setup */
         reset_current_kprobe();
         preempt_enable_no_resched();
         return 1;
     }
 
     if (p->ainsn.boostable >= 0) {
         ret = try_to_emulate(p, regs);
 
         if (ret > 0) {
             if (p->post_handler)
                 p->post_handler(p, regs, 0);
 
             kcb->kprobe_status = KPROBE_HIT_SSDONE;
             reset_current_kprobe();
             preempt_enable_no_resched();
             return 1;
         }
     }
     prepare_singlestep(p, regs);
     kcb->kprobe_status = KPROBE_HIT_SS;
     return 1;
 
 no_kprobe:
     preempt_enable_no_resched();
     return ret;
 }
 NOKPROBE_SYMBOL(kprobe_handler);
 
 /*
  * Function return probe trampoline:
  *  - init_kprobes() establishes a probepoint here
  *  - When the probed function returns, this probe
  *      causes the handlers to fire
  */
 asm(".global __kretprobe_trampoline\n"
     ".type __kretprobe_trampoline, @function\n"
     "__kretprobe_trampoline:\n"
     "nop\n"
     "blr\n"
     ".size __kretprobe_trampoline, .-__kretprobe_trampoline\n");
 
 /*
  * Called when the probe at kretprobe trampoline is hit
  */
 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 {
     unsigned long orig_ret_address;
 
     orig_ret_address = __kretprobe_trampoline_handler(regs, NULL);
     /*
      * We get here through one of two paths:
      * 1. by taking a trap -> kprobe_handler() -> here
      * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
      *
      * When going back through (1), we need regs->nip to be setup properly
      * as it is used to determine the return address from the trap.
      * For (2), since nip is not honoured with optprobes, we instead setup
      * the link register properly so that the subsequent 'blr' in
      * __kretprobe_trampoline jumps back to the right instruction.
      *
      * For nip, we should set the address to the previous instruction since
      * we end up emulating it in kprobe_handler(), which increments the nip
      * again.
      */
     regs_set_return_ip(regs, orig_ret_address - 4);
     regs->link = orig_ret_address;
 
     return 0;
 }
 NOKPROBE_SYMBOL(trampoline_probe_handler);
 
 /*
  * Called after single-stepping.  p->addr is the address of the
  * instruction whose first byte has been replaced by the "breakpoint"
  * instruction.  To avoid the SMP problems that can occur when we
  * temporarily put back the original opcode to single-step, we
  * single-stepped a copy of the instruction.  The address of this
  * copy is p->ainsn.insn.
  */
 int kprobe_post_handler(struct pt_regs *regs)
 {
     int len;
     struct kprobe *cur = kprobe_running();
     struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
     if (!cur || user_mode(regs))
         return 0;
 
     len = ppc_inst_len(ppc_inst_read(cur->ainsn.insn));
     /* make sure we got here for instruction we have a kprobe on */
     if (((unsigned long)cur->ainsn.insn + len) != regs->nip)
         return 0;
 
     if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
         kcb->kprobe_status = KPROBE_HIT_SSDONE;
         cur->post_handler(cur, regs, 0);
     }
 
     /* Adjust nip to after the single-stepped instruction */
     regs_set_return_ip(regs, (unsigned long)cur->addr + len);
     regs_set_return_msr(regs, regs->msr | kcb->kprobe_saved_msr);
 
     /*Restore back the original saved kprobes variables and continue. */
     if (kcb->kprobe_status == KPROBE_REENTER) {
         restore_previous_kprobe(kcb);
         goto out;
     }
     reset_current_kprobe();
 out:
     preempt_enable_no_resched();
 
     /*
      * if somebody else is singlestepping across a probe point, msr
      * will have DE/SE set, in which case, continue the remaining processing
      * of do_debug, as if this is not a probe hit.
      */
     if (regs->msr & MSR_SINGLESTEP)
         return 0;
 
     return 1;
 }
 NOKPROBE_SYMBOL(kprobe_post_handler);
 
 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
     struct kprobe *cur = kprobe_running();
     struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
     const struct exception_table_entry *entry;
 
     switch(kcb->kprobe_status) {
     case KPROBE_HIT_SS:
     case KPROBE_REENTER:
         /*
          * We are here because the instruction being single
          * stepped caused a page fault. We reset the current
          * kprobe and the nip points back to the probe address
          * and allow the page fault handler to continue as a
          * normal page fault.
          */
         regs_set_return_ip(regs, (unsigned long)cur->addr);
         /* Turn off 'trace' bits */
         regs_set_return_msr(regs,
             (regs->msr & ~MSR_SINGLESTEP) |
             kcb->kprobe_saved_msr);
         if (kcb->kprobe_status == KPROBE_REENTER)
             restore_previous_kprobe(kcb);
         else
             reset_current_kprobe();
         preempt_enable_no_resched();
         break;
     case KPROBE_HIT_ACTIVE:
     case KPROBE_HIT_SSDONE:
         /*
          * In case the user-specified fault handler returned
          * zero, try to fix up.
          */
         if ((entry = search_exception_tables(regs->nip)) != NULL) {
             regs_set_return_ip(regs, extable_fixup(entry));
             return 1;
         }
 
         /*
          * fixup_exception() could not handle it,
          * Let do_page_fault() fix it.
          */
         break;
     default:
         break;
     }
     return 0;
 }
 NOKPROBE_SYMBOL(kprobe_fault_handler);
 
 static struct kprobe trampoline_p = {
     .addr = (kprobe_opcode_t *) &__kretprobe_trampoline,
     .pre_handler = trampoline_probe_handler
 };
 
 int __init arch_init_kprobes(void)
 {
     return register_kprobe(&trampoline_p);
 }
 
 int arch_trampoline_kprobe(struct kprobe *p)
 {
     if (p->addr == (kprobe_opcode_t *)&__kretprobe_trampoline)
         return 1;
 
     return 0;
 }
 NOKPROBE_SYMBOL(arch_trampoline_kprobe);

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