arch/sparc/kernel/uprobes.c

   1 /*
   2  * User-space Probes (UProbes) for sparc
   3  *
   4  * Copyright (C) 2013 Oracle Inc.
   5  *
   6  * This program is free software: you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation, either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  *
  19  * Authors:
  20  *      Jose E. Marchesi <jose.marchesi@oracle.com>
  21  *      Eric Saint Etienne <eric.saint.etienne@oracle.com>
  22  */
  23
  24 #include <linux/kernel.h>
  25 #include <linux/highmem.h>
  26 #include <linux/uprobes.h>
  27 #include <linux/uaccess.h>
  28 #include <linux/sched.h> /* For struct task_struct */
  29 #include <linux/kdebug.h>
  30
  31 #include <asm/cacheflush.h>
  32 #include <linux/uaccess.h>
  33
  34 /* Compute the address of the breakpoint instruction and return it.
  35  *
  36  * Note that uprobe_get_swbp_addr is defined as a weak symbol in
  37  * kernel/events/uprobe.c.
  38  */
  39 unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
  40 {
  41         return instruction_pointer(regs);
  42 }
  43
  44 static void copy_to_page(struct page *page, unsigned long vaddr,
  45                          const void *src, int len)
  46 {
  47         void *kaddr = kmap_atomic(page);
  48
  49         memcpy(kaddr + (vaddr & ~PAGE_MASK), src, len);
  50         kunmap_atomic(kaddr);
  51 }
  52
  53 /* Fill in the xol area with the probed instruction followed by the
  54  * single-step trap.  Some fixups in the copied instruction are
  55  * performed at this point.
  56  *
  57  * Note that uprobe_xol_copy is defined as a weak symbol in
  58  * kernel/events/uprobe.c.
  59  */
  60 void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
  61                            void *src, unsigned long len)
  62 {
  63         const u32 stp_insn = UPROBE_STP_INSN;
  64         u32 insn = *(u32 *) src;
  65
  66         /* Branches annulling their delay slot must be fixed to not do
  67          * so.  Clearing the annul bit on these instructions we can be
  68          * sure the single-step breakpoint in the XOL slot will be
  69          * executed.
  70          */
  71
  72         u32 op = (insn >> 30) & 0x3;
  73         u32 op2 = (insn >> 22) & 0x7;
  74
  75         if (op == 0 &&
  76             (op2 == 1 || op2 == 2 || op2 == 3 || op2 == 5 || op2 == 6) &&
  77             (insn & ANNUL_BIT) == ANNUL_BIT)
  78                 insn &= ~ANNUL_BIT;
  79
  80         copy_to_page(page, vaddr, &insn, len);
  81         copy_to_page(page, vaddr+len, &stp_insn, 4);
  82 }
  83
  84
  85 /* Instruction analysis/validity.
  86  *
  87  * This function returns 0 on success or a -ve number on error.
  88  */
  89 int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
  90                              struct mm_struct *mm, unsigned long addr)
  91 {
  92         /* Any unsupported instruction?  Then return -EINVAL  */
  93         return 0;
  94 }
  95
  96 /* If INSN is a relative control transfer instruction, return the
  97  * corrected branch destination value.
  98  *
  99  * Note that regs->tpc and regs->tnpc still hold the values of the
 100  * program counters at the time of the single-step trap due to the
 101  * execution of the UPROBE_STP_INSN at utask->xol_vaddr + 4.
 102  *
 103  */
 104 static unsigned long relbranch_fixup(u32 insn, struct uprobe_task *utask,
 105                                      struct pt_regs *regs)
 106 {
 107         /* Branch not taken, no mods necessary.  */
 108         if (regs->tnpc == regs->tpc + 0x4UL)
 109                 return utask->autask.saved_tnpc + 0x4UL;
 110
 111         /* The three cases are call, branch w/prediction,
 112          * and traditional branch.
 113          */
 114         if ((insn & 0xc0000000) == 0x40000000 ||
 115             (insn & 0xc1c00000) == 0x00400000 ||
 116             (insn & 0xc1c00000) == 0x00800000) {
 117                 unsigned long real_pc = (unsigned long) utask->vaddr;
 118                 unsigned long ixol_addr = utask->xol_vaddr;
 119
 120                 /* The instruction did all the work for us
 121                  * already, just apply the offset to the correct
 122                  * instruction location.
 123                  */
 124                 return (real_pc + (regs->tnpc - ixol_addr));
 125         }
 126
 127         /* It is jmpl or some other absolute PC modification instruction,
 128          * leave NPC as-is.
 129          */
 130         return regs->tnpc;
 131 }
 132
 133 /* If INSN is an instruction which writes its PC location
 134  * into a destination register, fix that up.
 135  */
 136 static int retpc_fixup(struct pt_regs *regs, u32 insn,
 137                        unsigned long real_pc)
 138 {
 139         unsigned long *slot = NULL;
 140         int rc = 0;
 141
 142         /* Simplest case is 'call', which always uses %o7 */
 143         if ((insn & 0xc0000000) == 0x40000000)
 144                 slot = &regs->u_regs[UREG_I7];
 145
 146         /* 'jmpl' encodes the register inside of the opcode */
 147         if ((insn & 0xc1f80000) == 0x81c00000) {
 148                 unsigned long rd = ((insn >> 25) & 0x1f);
 149
 150                 if (rd <= 15) {
 151                         slot = &regs->u_regs[rd];
 152                 } else {
 153                         unsigned long fp = regs->u_regs[UREG_FP];
 154                         /* Hard case, it goes onto the stack. */
 155                         flushw_all();
 156
 157                         rd -= 16;
 158                         if (test_thread_64bit_stack(fp)) {
 159                                 unsigned long __user *uslot =
 160                         (unsigned long __user *) (fp + STACK_BIAS) + rd;
 161                                 rc = __put_user(real_pc, uslot);
 162                         } else {
 163                                 unsigned int __user *uslot = (unsigned int
 164                                                 __user *) fp + rd;
 165                                 rc = __put_user((u32) real_pc, uslot);
 166                         }
 167                 }
 168         }
 169         if (slot != NULL)
 170                 *slot = real_pc;
 171         return rc;
 172 }
 173
 174 /* Single-stepping can be avoided for certain instructions: NOPs and
 175  * instructions that can be emulated.  This function determines
 176  * whether the instruction where the uprobe is installed falls in one
 177  * of these cases and emulates it.
 178  *
 179  * This function returns true if the single-stepping can be skipped,
 180  * false otherwise.
 181  */
 182 bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 183 {
 184         /* We currently only emulate NOP instructions.
 185          */
 186
 187         if (auprobe->ixol == (1 << 24)) {
 188                 regs->tnpc += 4;
 189                 regs->tpc += 4;
 190                 return true;
 191         }
 192
 193         return false;
 194 }
 195
 196 /* Prepare to execute out of line.  At this point
 197  * current->utask->xol_vaddr points to an allocated XOL slot properly
 198  * initialized with the original instruction and the single-stepping
 199  * trap instruction.
 200  *
 201  * This function returns 0 on success, any other number on error.
 202  */
 203 int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 204 {
 205         struct uprobe_task *utask = current->utask;
 206         struct arch_uprobe_task *autask = &current->utask->autask;
 207
 208         /* Save the current program counters so they can be restored
 209          * later.
 210          */
 211         autask->saved_tpc = regs->tpc;
 212         autask->saved_tnpc = regs->tnpc;
 213
 214         /* Adjust PC and NPC so the first instruction in the XOL slot
 215          * will be executed by the user task.
 216          */
 217         instruction_pointer_set(regs, utask->xol_vaddr);
 218
 219         return 0;
 220 }
 221
 222 /* Prepare to resume execution after the single-step.  Called after
 223  * single-stepping. To avoid the SMP problems that can occur when we
 224  * temporarily put back the original opcode to single-step, we
 225  * single-stepped a copy of the instruction.
 226  *
 227  * This function returns 0 on success, any other number on error.
 228  */
 229 int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 230 {
 231         struct uprobe_task *utask = current->utask;
 232         struct arch_uprobe_task *autask = &utask->autask;
 233         u32 insn = auprobe->ixol;
 234         int rc = 0;
 235
 236         if (utask->state == UTASK_SSTEP_ACK) {
 237                 regs->tnpc = relbranch_fixup(insn, utask, regs);
 238                 regs->tpc = autask->saved_tnpc;
 239                 rc =  retpc_fixup(regs, insn, (unsigned long) utask->vaddr);
 240         } else {
 241                 regs->tnpc = utask->vaddr+4;
 242                 regs->tpc = autask->saved_tnpc+4;
 243         }
 244         return rc;
 245 }
 246
 247 /* Handler for uprobe traps.  This is called from the traps table and
 248  * triggers the proper die notification.
 249  */
 250 asmlinkage void uprobe_trap(struct pt_regs *regs,
 251                             unsigned long trap_level)
 252 {
 253         BUG_ON(trap_level != 0x173 && trap_level != 0x174);
 254
 255         /* We are only interested in user-mode code.  Uprobe traps
 256          * shall not be present in kernel code.
 257          */
 258         if (!user_mode(regs)) {
 259                 local_irq_enable();
 260                 bad_trap(regs, trap_level);
 261                 return;
 262         }
 263
 264         /* trap_level == 0x173 --> ta 0x73
 265          * trap_level == 0x174 --> ta 0x74
 266          */
 267         if (notify_die((trap_level == 0x173) ? DIE_BPT : DIE_SSTEP,
 268                                 (trap_level == 0x173) ? "bpt" : "sstep",
 269                                 regs, 0, trap_level, SIGTRAP) != NOTIFY_STOP)
 270                 bad_trap(regs, trap_level);
 271 }
 272
 273 /* Callback routine for handling die notifications.
 274 */
 275 int arch_uprobe_exception_notify(struct notifier_block *self,
 276                                  unsigned long val, void *data)
 277 {
 278         int ret = NOTIFY_DONE;
 279         struct die_args *args = (struct die_args *)data;
 280
 281         /* We are only interested in userspace traps */
 282         if (args->regs && !user_mode(args->regs))
 283                 return NOTIFY_DONE;
 284
 285         switch (val) {
 286         case DIE_BPT:
 287                 if (uprobe_pre_sstep_notifier(args->regs))
 288                         ret = NOTIFY_STOP;
 289                 break;
 290
 291         case DIE_SSTEP:
 292                 if (uprobe_post_sstep_notifier(args->regs))
 293                         ret = NOTIFY_STOP;
 294
 295         default:
 296                 break;
 297         }
 298
 299         return ret;
 300 }
 301
 302 /* This function gets called when a XOL instruction either gets
 303  * trapped or the thread has a fatal signal, so reset the instruction
 304  * pointer to its probed address.
 305  */
 306 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 307 {
 308         struct uprobe_task *utask = current->utask;
 309
 310         instruction_pointer_set(regs, utask->vaddr);
 311 }
 312
 313 /* If xol insn itself traps and generates a signal(Say,
 314  * SIGILL/SIGSEGV/etc), then detect the case where a singlestepped
 315  * instruction jumps back to its own address.
 316  */
 317 bool arch_uprobe_xol_was_trapped(struct task_struct *t)
 318 {
 319         return false;
 320 }
 321
 322 unsigned long
 323 arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr,
 324                                   struct pt_regs *regs)
 325 {
 326         unsigned long orig_ret_vaddr = regs->u_regs[UREG_I7];
 327
 328         regs->u_regs[UREG_I7] = trampoline_vaddr-8;
 329
 330         return orig_ret_vaddr + 8;
 331 }