arch/powerpc/kernel/optprobes.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Code for Kernel probes Jump optimization.
   4  *
   5  * Copyright 2017, Anju T, IBM Corp.
   6  */
   7
   8 #include <linux/kprobes.h>
   9 #include <linux/jump_label.h>
  10 #include <linux/types.h>
  11 #include <linux/slab.h>
  12 #include <linux/list.h>
  13 #include <asm/kprobes.h>
  14 #include <asm/ptrace.h>
  15 #include <asm/cacheflush.h>
  16 #include <asm/code-patching.h>
  17 #include <asm/sstep.h>
  18 #include <asm/ppc-opcode.h>
  19 #include <asm/inst.h>
  20
  21 #define TMPL_CALL_HDLR_IDX      (optprobe_template_call_handler - optprobe_template_entry)
  22 #define TMPL_EMULATE_IDX        (optprobe_template_call_emulate - optprobe_template_entry)
  23 #define TMPL_RET_IDX            (optprobe_template_ret - optprobe_template_entry)
  24 #define TMPL_OP_IDX             (optprobe_template_op_address - optprobe_template_entry)
  25 #define TMPL_INSN_IDX           (optprobe_template_insn - optprobe_template_entry)
  26 #define TMPL_END_IDX            (optprobe_template_end - optprobe_template_entry)
  27
  28 static bool insn_page_in_use;
  29
  30 void *alloc_optinsn_page(void)
  31 {
  32         if (insn_page_in_use)
  33                 return NULL;
  34         insn_page_in_use = true;
  35         return &optinsn_slot;
  36 }
  37
  38 void free_optinsn_page(void *page)
  39 {
  40         insn_page_in_use = false;
  41 }
  42
  43 /*
  44  * Check if we can optimize this probe. Returns NIP post-emulation if this can
  45  * be optimized and 0 otherwise.
  46  */
  47 static unsigned long can_optimize(struct kprobe *p)
  48 {
  49         struct pt_regs regs;
  50         struct instruction_op op;
  51         unsigned long nip = 0;
  52         unsigned long addr = (unsigned long)p->addr;
  53
  54         /*
  55          * kprobe placed for kretprobe during boot time
  56          * has a 'nop' instruction, which can be emulated.
  57          * So further checks can be skipped.
  58          */
  59         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
  60                 return addr + sizeof(kprobe_opcode_t);
  61
  62         /*
  63          * We only support optimizing kernel addresses, but not
  64          * module addresses.
  65          *
  66          * FIXME: Optimize kprobes placed in module addresses.
  67          */
  68         if (!is_kernel_addr(addr))
  69                 return 0;
  70
  71         memset(&regs, 0, sizeof(struct pt_regs));
  72         regs.nip = addr;
  73         regs.trap = 0x0;
  74         regs.msr = MSR_KERNEL;
  75
  76         /*
  77          * Kprobe placed in conditional branch instructions are
  78          * not optimized, as we can't predict the nip prior with
  79          * dummy pt_regs and can not ensure that the return branch
  80          * from detour buffer falls in the range of address (i.e 32MB).
  81          * A branch back from trampoline is set up in the detour buffer
  82          * to the nip returned by the analyse_instr() here.
  83          *
  84          * Ensure that the instruction is not a conditional branch,
  85          * and that can be emulated.
  86          */
  87         if (!is_conditional_branch(ppc_inst_read(p->ainsn.insn)) &&
  88             analyse_instr(&op, &regs, ppc_inst_read(p->ainsn.insn)) == 1) {
  89                 emulate_update_regs(&regs, &op);
  90                 nip = regs.nip;
  91         }
  92
  93         return nip;
  94 }
  95
  96 static void optimized_callback(struct optimized_kprobe *op,
  97                                struct pt_regs *regs)
  98 {
  99         /* This is possible if op is under delayed unoptimizing */
 100         if (kprobe_disabled(&op->kp))
 101                 return;
 102
 103         preempt_disable();
 104
 105         if (kprobe_running()) {
 106                 kprobes_inc_nmissed_count(&op->kp);
 107         } else {
 108                 __this_cpu_write(current_kprobe, &op->kp);
 109                 regs_set_return_ip(regs, (unsigned long)op->kp.addr);
 110                 get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 111                 opt_pre_handler(&op->kp, regs);
 112                 __this_cpu_write(current_kprobe, NULL);
 113         }
 114
 115         preempt_enable_no_resched();
 116 }
 117 NOKPROBE_SYMBOL(optimized_callback);
 118
 119 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 120 {
 121         if (op->optinsn.insn) {
 122                 free_optinsn_slot(op->optinsn.insn, 1);
 123                 op->optinsn.insn = NULL;
 124         }
 125 }
 126
 127 static void patch_imm32_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
 128 {
 129         patch_instruction(addr++, ppc_inst(PPC_RAW_LIS(reg, PPC_HI(val))));
 130         patch_instruction(addr, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_LO(val))));
 131 }
 132
 133 /*
 134  * Generate instructions to load provided immediate 64-bit value
 135  * to register 'reg' and patch these instructions at 'addr'.
 136  */
 137 static void patch_imm64_load_insns(unsigned long long val, int reg, kprobe_opcode_t *addr)
 138 {
 139         patch_instruction(addr++, ppc_inst(PPC_RAW_LIS(reg, PPC_HIGHEST(val))));
 140         patch_instruction(addr++, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_HIGHER(val))));
 141         patch_instruction(addr++, ppc_inst(PPC_RAW_SLDI(reg, reg, 32)));
 142         patch_instruction(addr++, ppc_inst(PPC_RAW_ORIS(reg, reg, PPC_HI(val))));
 143         patch_instruction(addr, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_LO(val))));
 144 }
 145
 146 static void patch_imm_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
 147 {
 148         if (IS_ENABLED(CONFIG_PPC64))
 149                 patch_imm64_load_insns(val, reg, addr);
 150         else
 151                 patch_imm32_load_insns(val, reg, addr);
 152 }
 153
 154 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 155 {
 156         struct ppc_inst branch_op_callback, branch_emulate_step, temp;
 157         unsigned long op_callback_addr, emulate_step_addr;
 158         kprobe_opcode_t *buff;
 159         long b_offset;
 160         unsigned long nip, size;
 161         int rc, i;
 162
 163         nip = can_optimize(p);
 164         if (!nip)
 165                 return -EILSEQ;
 166
 167         /* Allocate instruction slot for detour buffer */
 168         buff = get_optinsn_slot();
 169         if (!buff)
 170                 return -ENOMEM;
 171
 172         /*
 173          * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
 174          *
 175          * The target address has to be relatively nearby, to permit use
 176          * of branch instruction in powerpc, because the address is specified
 177          * in an immediate field in the instruction opcode itself, ie 24 bits
 178          * in the opcode specify the address. Therefore the address should
 179          * be within 32MB on either side of the current instruction.
 180          */
 181         b_offset = (unsigned long)buff - (unsigned long)p->addr;
 182         if (!is_offset_in_branch_range(b_offset))
 183                 goto error;
 184
 185         /* Check if the return address is also within 32MB range */
 186         b_offset = (unsigned long)(buff + TMPL_RET_IDX) - nip;
 187         if (!is_offset_in_branch_range(b_offset))
 188                 goto error;
 189
 190         /* Setup template */
 191         /* We can optimize this via patch_instruction_window later */
 192         size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
 193         pr_devel("Copying template to %p, size %lu\n", buff, size);
 194         for (i = 0; i < size; i++) {
 195                 rc = patch_instruction(buff + i, ppc_inst(*(optprobe_template_entry + i)));
 196                 if (rc < 0)
 197                         goto error;
 198         }
 199
 200         /*
 201          * Fixup the template with instructions to:
 202          * 1. load the address of the actual probepoint
 203          */
 204         patch_imm_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
 205
 206         /*
 207          * 2. branch to optimized_callback() and emulate_step()
 208          */
 209         op_callback_addr = ppc_kallsyms_lookup_name("optimized_callback");
 210         emulate_step_addr = ppc_kallsyms_lookup_name("emulate_step");
 211         if (!op_callback_addr || !emulate_step_addr) {
 212                 WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
 213                 goto error;
 214         }
 215
 216         rc = create_branch(&branch_op_callback, buff + TMPL_CALL_HDLR_IDX,
 217                            op_callback_addr, BRANCH_SET_LINK);
 218
 219         rc |= create_branch(&branch_emulate_step, buff + TMPL_EMULATE_IDX,
 220                             emulate_step_addr, BRANCH_SET_LINK);
 221
 222         if (rc)
 223                 goto error;
 224
 225         patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
 226         patch_instruction(buff + TMPL_EMULATE_IDX, branch_emulate_step);
 227
 228         /*
 229          * 3. load instruction to be emulated into relevant register, and
 230          */
 231         if (IS_ENABLED(CONFIG_PPC64)) {
 232                 temp = ppc_inst_read(p->ainsn.insn);
 233                 patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
 234         } else {
 235                 patch_imm_load_insns((unsigned long)p->ainsn.insn, 4, buff + TMPL_INSN_IDX);
 236         }
 237
 238         /*
 239          * 4. branch back from trampoline
 240          */
 241         patch_branch(buff + TMPL_RET_IDX, nip, 0);
 242
 243         flush_icache_range((unsigned long)buff, (unsigned long)(&buff[TMPL_END_IDX]));
 244
 245         op->optinsn.insn = buff;
 246
 247         return 0;
 248
 249 error:
 250         free_optinsn_slot(buff, 0);
 251         return -ERANGE;
 252
 253 }
 254
 255 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
 256 {
 257         return optinsn->insn != NULL;
 258 }
 259
 260 /*
 261  * On powerpc, Optprobes always replaces one instruction (4 bytes
 262  * aligned and 4 bytes long). It is impossible to encounter another
 263  * kprobe in this address range. So always return 0.
 264  */
 265 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 266 {
 267         return 0;
 268 }
 269
 270 void arch_optimize_kprobes(struct list_head *oplist)
 271 {
 272         struct ppc_inst instr;
 273         struct optimized_kprobe *op;
 274         struct optimized_kprobe *tmp;
 275
 276         list_for_each_entry_safe(op, tmp, oplist, list) {
 277                 /*
 278                  * Backup instructions which will be replaced
 279                  * by jump address
 280                  */
 281                 memcpy(op->optinsn.copied_insn, op->kp.addr, RELATIVEJUMP_SIZE);
 282                 create_branch(&instr, op->kp.addr, (unsigned long)op->optinsn.insn, 0);
 283                 patch_instruction(op->kp.addr, instr);
 284                 list_del_init(&op->list);
 285         }
 286 }
 287
 288 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 289 {
 290         arch_arm_kprobe(&op->kp);
 291 }
 292
 293 void arch_unoptimize_kprobes(struct list_head *oplist, struct list_head *done_list)
 294 {
 295         struct optimized_kprobe *op;
 296         struct optimized_kprobe *tmp;
 297
 298         list_for_each_entry_safe(op, tmp, oplist, list) {
 299                 arch_unoptimize_kprobe(op);
 300                 list_move(&op->list, done_list);
 301         }
 302 }
 303
 304 int arch_within_optimized_kprobe(struct optimized_kprobe *op, unsigned long addr)
 305 {
 306         return ((unsigned long)op->kp.addr <= addr &&
 307                 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
 308 }