/* * Kernel Probes (KProbes) * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright (C) IBM Corporation, 2002, 2004 * * 2002-Oct Created by Vamsi Krishna S Kernel * Probes initial implementation ( includes contributions from * Rusty Russell). * 2004-July Suparna Bhattacharya added jumper probes * interface to access function arguments. * 2004-Oct Jim Keniston and Prasanna S Panchamukhi * adapted for x86_64 from i386. * 2005-Mar Roland McGrath * Fixed to handle %rip-relative addressing mode correctly. * 2005-May Hien Nguyen , Jim Keniston * and Prasanna S Panchamukhi * added function-return probes. * 2005-May Rusty Lynch * Added function return probes functionality * 2006-Feb Masami Hiramatsu added * kprobe-booster and kretprobe-booster for i386. * 2007-Dec Masami Hiramatsu added kprobe-booster * and kretprobe-booster for x86-64 * 2007-Dec Masami Hiramatsu , Arjan van de Ven * and Jim Keniston * unified x86 kprobes code. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "common.h" void jprobe_return_end(void); DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL; DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk); #define stack_addr(regs) ((unsigned long *)kernel_stack_pointer(regs)) #define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\ (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) | \ (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) | \ (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) | \ (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf)) \ << (row % 32)) /* * Undefined/reserved opcodes, conditional jump, Opcode Extension * Groups, and some special opcodes can not boost. * This is non-const and volatile to keep gcc from statically * optimizing it out, as variable_test_bit makes gcc think only * *(unsigned long*) is used. */ static volatile u32 twobyte_is_boostable[256 / 32] = { /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ /* ---------------------------------------------- */ W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */ W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 10 */ W(0x20, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 20 */ W(0x30, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 30 */ W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */ W(0x50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 50 */ W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1) | /* 60 */ W(0x70, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1) , /* 70 */ W(0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 80 */ W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */ W(0xa0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* a0 */ W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1) , /* b0 */ W(0xc0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* c0 */ W(0xd0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) , /* d0 */ W(0xe0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* e0 */ W(0xf0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0) /* f0 */ /* ----------------------------------------------- */ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ }; #undef W struct kretprobe_blackpoint kretprobe_blacklist[] = { {"__switch_to", }, /* This function switches only current task, but doesn't switch kernel stack.*/ {NULL, NULL} /* Terminator */ }; const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist); static void __kprobes __synthesize_relative_insn(void *from, void *to, u8 op) { struct __arch_relative_insn { u8 op; s32 raddr; } __packed *insn; insn = (struct __arch_relative_insn *)from; insn->raddr = (s32)((long)(to) - ((long)(from) + 5)); insn->op = op; } /* Insert a jump instruction at address 'from', which jumps to address 'to'.*/ void __kprobes synthesize_reljump(void *from, void *to) { __synthesize_relative_insn(from, to, RELATIVEJUMP_OPCODE); } /* Insert a call instruction at address 'from', which calls address 'to'.*/ void __kprobes synthesize_relcall(void *from, void *to) { __synthesize_relative_insn(from, to, RELATIVECALL_OPCODE); } /* * Skip the prefixes of the instruction. */ static kprobe_opcode_t *__kprobes skip_prefixes(kprobe_opcode_t *insn) { insn_attr_t attr; attr = inat_get_opcode_attribute((insn_byte_t)*insn); while (inat_is_legacy_prefix(attr)) { insn++; attr = inat_get_opcode_attribute((insn_byte_t)*insn); } #ifdef CONFIG_X86_64 if (inat_is_rex_prefix(attr)) insn++; #endif return insn; } /* * Returns non-zero if opcode is boostable. * RIP relative instructions are adjusted at copying time in 64 bits mode */ int __kprobes can_boost(kprobe_opcode_t *opcodes) { kprobe_opcode_t opcode; kprobe_opcode_t *orig_opcodes = opcodes; if (search_exception_tables((unsigned long)opcodes)) return 0; /* Page fault may occur on this address. */ retry: if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1) return 0; opcode = *(opcodes++); /* 2nd-byte opcode */ if (opcode == 0x0f) { if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1) return 0; return test_bit(*opcodes, (unsigned long *)twobyte_is_boostable); } switch (opcode & 0xf0) { #ifdef CONFIG_X86_64 case 0x40: goto retry; /* REX prefix is boostable */ #endif case 0x60: if (0x63 < opcode && opcode < 0x67) goto retry; /* prefixes */ /* can't boost Address-size override and bound */ return (opcode != 0x62 && opcode != 0x67); case 0x70: return 0; /* can't boost conditional jump */ case 0xc0: /* can't boost software-interruptions */ return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf; case 0xd0: /* can boost AA* and XLAT */ return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7); case 0xe0: /* can boost in/out and absolute jmps */ return ((opcode & 0x04) || opcode == 0xea); case 0xf0: if ((opcode & 0x0c) == 0 && opcode != 0xf1) goto retry; /* lock/rep(ne) prefix */ /* clear and set flags are boostable */ return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe)); default: /* segment override prefixes are boostable */ if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e) goto retry; /* prefixes */ /* CS override prefix and call are not boostable */ return (opcode != 0x2e && opcode != 0x9a); } } static unsigned long __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr) { struct kprobe *kp; kp = get_kprobe((void *)addr); /* There is no probe, return original address */ if (!kp) return addr; /* * Basically, kp->ainsn.insn has an original instruction. * However, RIP-relative instruction can not do single-stepping * at different place, __copy_instruction() tweaks the displacement of * that instruction. In that case, we can't recover the instruction * from the kp->ainsn.insn. * * On the other hand, kp->opcode has a copy of the first byte of * the probed instruction, which is overwritten by int3. And * the instruction at kp->addr is not modified by kprobes except * for the first byte, we can recover the original instruction * from it and kp->opcode. */ memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t)); buf[0] = kp->opcode; return (unsigned long)buf; } /* * Recover the probed instruction at addr for further analysis. * Caller must lock kprobes by kprobe_mutex, or disable preemption * for preventing to release referencing kprobes. */ unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr) { unsigned long __addr; __addr = __recover_optprobed_insn(buf, addr); if (__addr != addr) return __addr; return __recover_probed_insn(buf, addr); } /* Check if paddr is at an instruction boundary */ static int __kprobes can_probe(unsigned long paddr) { unsigned long addr, __addr, offset = 0; struct insn insn; kprobe_opcode_t buf[MAX_INSN_SIZE]; if (!kallsyms_lookup_size_offset(paddr, NULL, &offset)) return 0; /* Decode instructions */ addr = paddr - offset; while (addr < paddr) { /* * Check if the instruction has been modified by another * kprobe, in which case we replace the breakpoint by the * original instruction in our buffer. * Also, jump optimization will change the breakpoint to * relative-jump. Since the relative-jump itself is * normally used, we just go through if there is no kprobe. */ __addr = recover_probed_instruction(buf, addr); kernel_insn_init(&insn, (void *)__addr); insn_get_length(&insn); /* * Another debugging subsystem might insert this breakpoint. * In that case, we can't recover it. */ if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION) return 0; addr += insn.length; } return (addr == paddr); } /* * Returns non-zero if opcode modifies the interrupt flag. */ static int __kprobes is_IF_modifier(kprobe_opcode_t *insn) { /* Skip prefixes */ insn = skip_prefixes(insn); switch (*insn) { case 0xfa: /* cli */ case 0xfb: /* sti */ case 0xcf: /* iret/iretd */ case 0x9d: /* popf/popfd */ return 1; } return 0; } /* * Copy an instruction and adjust the displacement if the instruction * uses the %rip-relative addressing mode. * If it does, Return the address of the 32-bit displacement word. * If not, return null. * Only applicable to 64-bit x86. */ int __kprobes __copy_instruction(u8 *dest, u8 *src) { struct insn insn; kprobe_opcode_t buf[MAX_INSN_SIZE]; kernel_insn_init(&insn, (void *)recover_probed_instruction(buf, (unsigned long)src)); insn_get_length(&insn); /* Another subsystem puts a breakpoint, failed to recover */ if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION) return 0; memcpy(dest, insn.kaddr, insn.length); #ifdef CONFIG_X86_64 if (insn_rip_relative(&insn)) { s64 newdisp; u8 *disp; kernel_insn_init(&insn, dest); insn_get_displacement(&insn); /* * The copied instruction uses the %rip-relative addressing * mode. Adjust the displacement for the difference between * the original location of this instruction and the location * of the copy that will actually be run. The tricky bit here * is making sure that the sign extension happens correctly in * this calculation, since we need a signed 32-bit result to * be sign-extended to 64 bits when it's added to the %rip * value and yield the same 64-bit result that the sign- * extension of the original signed 32-bit displacement would * have given. */ newdisp = (u8 *) src + (s64) insn.displacement.value - (u8 *) dest; if ((s64) (s32) newdisp != newdisp) { pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp); pr_err("\tSrc: %p, Dest: %p, old disp: %x\n", src, dest, insn.displacement.value); return 0; } disp = (u8 *) dest + insn_offset_displacement(&insn); *(s32 *) disp = (s32) newdisp; } #endif return insn.length; } static int __kprobes arch_copy_kprobe(struct kprobe *p) { int ret; /* Copy an instruction with recovering if other optprobe modifies it.*/ ret = __copy_instruction(p->ainsn.insn, p->addr); if (!ret) return -EINVAL; /* * __copy_instruction can modify the displacement of the instruction, * but it doesn't affect boostable check. */ if (can_boost(p->ainsn.insn)) p->ainsn.boostable = 0; else p->ainsn.boostable = -1; /* Check whether the instruction modifies Interrupt Flag or not */ p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn); /* Also, displacement change doesn't affect the first byte */ p->opcode = p->ainsn.insn[0]; return 0; } int __kprobes arch_prepare_kprobe(struct kprobe *p) { if (alternatives_text_reserved(p->addr, p->addr)) return -EINVAL; if (!can_probe((unsigned long)p->addr)) return -EILSEQ; /* insn: must be on special executable page on x86. */ p->ainsn.insn = get_insn_slot(); if (!p->ainsn.insn) return -ENOMEM; return arch_copy_kprobe(p); } void __kprobes arch_arm_kprobe(struct kprobe *p) { text_poke(p->addr, ((unsigned char []){BREAKPOINT_INSTRUCTION}), 1); } void __kprobes arch_disarm_kprobe(struct kprobe *p) { text_poke(p->addr, &p->opcode, 1); } void __kprobes arch_remove_kprobe(struct kprobe *p) { if (p->ainsn.insn) { free_insn_slot(p->ainsn.insn, (p->ainsn.boostable == 1)); p->ainsn.insn = NULL; } } static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb) { kcb->prev_kprobe.kp = kprobe_running(); kcb->prev_kprobe.status = kcb->kprobe_status; kcb->prev_kprobe.old_flags = kcb->kprobe_old_flags; kcb->prev_kprobe.saved_flags = kcb->kprobe_saved_flags; } static void __kprobes 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_old_flags = kcb->prev_kprobe.old_flags; kcb->kprobe_saved_flags = kcb->prev_kprobe.saved_flags; } static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { __this_cpu_write(current_kprobe, p); kcb->kprobe_saved_flags = kcb->kprobe_old_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF)); if (p->ainsn.if_modifier) kcb->kprobe_saved_flags &= ~X86_EFLAGS_IF; } static void __kprobes clear_btf(void) { if (test_thread_flag(TIF_BLOCKSTEP)) { unsigned long debugctl = get_debugctlmsr(); debugctl &= ~DEBUGCTLMSR_BTF; update_debugctlmsr(debugctl); } } static void __kprobes restore_btf(void) { if (test_thread_flag(TIF_BLOCKSTEP)) { unsigned long debugctl = get_debugctlmsr(); debugctl |= DEBUGCTLMSR_BTF; update_debugctlmsr(debugctl); } } void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs) { unsigned long *sara = stack_addr(regs); ri->ret_addr = (kprobe_opcode_t *) *sara; /* Replace the return addr with trampoline addr */ *sara = (unsigned long) &kretprobe_trampoline; } static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb, int reenter) { if (setup_detour_execution(p, regs, reenter)) return; #if !defined(CONFIG_PREEMPT) if (p->ainsn.boostable == 1 && !p->post_handler) { /* Boost up -- we can execute copied instructions directly */ if (!reenter) reset_current_kprobe(); /* * Reentering boosted probe doesn't reset current_kprobe, * nor set current_kprobe, because it doesn't use single * stepping. */ regs->ip = (unsigned long)p->ainsn.insn; preempt_enable_no_resched(); return; } #endif if (reenter) { save_previous_kprobe(kcb); set_current_kprobe(p, regs, kcb); kcb->kprobe_status = KPROBE_REENTER; } else kcb->kprobe_status = KPROBE_HIT_SS; /* Prepare real single stepping */ clear_btf(); regs->flags |= X86_EFLAGS_TF; regs->flags &= ~X86_EFLAGS_IF; /* single step inline if the instruction is an int3 */ if (p->opcode == BREAKPOINT_INSTRUCTION) regs->ip = (unsigned long)p->addr; else regs->ip = (unsigned long)p->ainsn.insn; } /* * We have reentered the kprobe_handler(), since another probe was hit while * within the handler. We save the original kprobes variables and just single * step on the instruction of the new probe without calling any user handlers. */ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { switch (kcb->kprobe_status) { case KPROBE_HIT_SSDONE: case KPROBE_HIT_ACTIVE: kprobes_inc_nmissed_count(p); setup_singlestep(p, regs, kcb, 1); break; case KPROBE_HIT_SS: /* A probe has been hit in the codepath leading up to, or just * after, single-stepping of a probed instruction. This entire * codepath should strictly reside in .kprobes.text section. * Raise a BUG or we'll continue in an endless reentering loop * and eventually a stack overflow. */ printk(KERN_WARNING "Unrecoverable kprobe detected at %p.\n", p->addr); dump_kprobe(p); BUG(); default: /* impossible cases */ WARN_ON(1); return 0; } return 1; } /* * Interrupts are disabled on entry as trap3 is an interrupt gate and they * remain disabled throughout this function. */ static int __kprobes kprobe_handler(struct pt_regs *regs) { kprobe_opcode_t *addr; struct kprobe *p; struct kprobe_ctlblk *kcb; addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t)); /* * We don't want to be preempted for the entire * duration of kprobe processing. We conditionally * re-enable preemption at the end of this function, * and also in reenter_kprobe() and setup_singlestep(). */ preempt_disable(); kcb = get_kprobe_ctlblk(); p = get_kprobe(addr); if (p) { if (kprobe_running()) { if (reenter_kprobe(p, regs, kcb)) return 1; } else { set_current_kprobe(p, regs, kcb); kcb->kprobe_status = KPROBE_HIT_ACTIVE; /* * If we have no pre-handler or it returned 0, we * continue with normal processing. If we have a * pre-handler and it returned non-zero, it prepped * for calling the break_handler below on re-entry * for jprobe processing, so get out doing nothing * more here. */ if (!p->pre_handler || !p->pre_handler(p, regs)) setup_singlestep(p, regs, kcb, 0); return 1; } } else if (*addr != BREAKPOINT_INSTRUCTION) { /* * 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. * Back up over the (now missing) int3 and run * the original instruction. */ regs->ip = (unsigned long)addr; preempt_enable_no_resched(); return 1; } else if (kprobe_running()) { p = __this_cpu_read(current_kprobe); if (p->break_handler && p->break_handler(p, regs)) { if (!skip_singlestep(p, regs, kcb)) setup_singlestep(p, regs, kcb, 0); return 1; } } /* else: not a kprobe fault; let the kernel handle it */ preempt_enable_no_resched(); return 0; } /* * When a retprobed function returns, this code saves registers and * calls trampoline_handler() runs, which calls the kretprobe's handler. */ static void __used __kprobes kretprobe_trampoline_holder(void) { asm volatile ( ".global kretprobe_trampoline\n" "kretprobe_trampoline: \n" #ifdef CONFIG_X86_64 /* We don't bother saving the ss register */ " pushq %rsp\n" " pushfq\n" SAVE_REGS_STRING " movq %rsp, %rdi\n" " call trampoline_handler\n" /* Replace saved sp with true return address. */ " movq %rax, 152(%rsp)\n" RESTORE_REGS_STRING " popfq\n" #else " pushf\n" SAVE_REGS_STRING " movl %esp, %eax\n" " call trampoline_handler\n" /* Move flags to cs */ " movl 56(%esp), %edx\n" " movl %edx, 52(%esp)\n" /* Replace saved flags with true return address. */ " movl %eax, 56(%esp)\n" RESTORE_REGS_STRING " popf\n" #endif " ret\n"); } /* * Called from kretprobe_trampoline */ __visible __used __kprobes void *trampoline_handler(struct pt_regs *regs) { struct kretprobe_instance *ri = NULL; struct hlist_head *head, empty_rp; struct hlist_node *tmp; unsigned long flags, orig_ret_address = 0; unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline; kprobe_opcode_t *correct_ret_addr = NULL; INIT_HLIST_HEAD(&empty_rp); kretprobe_hash_lock(current, &head, &flags); /* fixup registers */ #ifdef CONFIG_X86_64 regs->cs = __KERNEL_CS; #else regs->cs = __KERNEL_CS | get_kernel_rpl(); regs->gs = 0; #endif regs->ip = trampoline_address; regs->orig_ax = ~0UL; /* * It is possible to have multiple instances associated with a given * task either because multiple functions in the call path have * return probes installed on them, and/or more than one * return probe was registered for a target function. * * We can handle this because: * - instances are always pushed into the head of the list * - when multiple return probes are registered for the same * function, the (chronologically) first instance's ret_addr * will be the real return address, and all the rest will * point to kretprobe_trampoline. */ hlist_for_each_entry_safe(ri, tmp, head, hlist) { if (ri->task != current) /* another task is sharing our hash bucket */ continue; orig_ret_address = (unsigned long)ri->ret_addr; if (orig_ret_address != trampoline_address) /* * This is the real return address. Any other * instances associated with this task are for * other calls deeper on the call stack */ break; } kretprobe_assert(ri, orig_ret_address, trampoline_address); correct_ret_addr = ri->ret_addr; hlist_for_each_entry_safe(ri, tmp, head, hlist) { if (ri->task != current) /* another task is sharing our hash bucket */ continue; orig_ret_address = (unsigned long)ri->ret_addr; if (ri->rp && ri->rp->handler) { __this_cpu_write(current_kprobe, &ri->rp->kp); get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; ri->ret_addr = correct_ret_addr; ri->rp->handler(ri, regs); __this_cpu_write(current_kprobe, NULL); } recycle_rp_inst(ri, &empty_rp); if (orig_ret_address != trampoline_address) /* * This is the real return address. Any other * instances associated with this task are for * other calls deeper on the call stack */ break; } kretprobe_hash_unlock(current, &flags); hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) { hlist_del(&ri->hlist); kfree(ri); } return (void *)orig_ret_address; } /* * Called after single-stepping. p->addr is the address of the * instruction whose first byte has been replaced by the "int 3" * 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. * * This function prepares to return from the post-single-step * interrupt. We have to fix up the stack as follows: * * 0) Except in the case of absolute or indirect jump or call instructions, * the new ip is relative to the copied instruction. We need to make * it relative to the original instruction. * * 1) If the single-stepped instruction was pushfl, then the TF and IF * flags are set in the just-pushed flags, and may need to be cleared. * * 2) If the single-stepped instruction was a call, the return address * that is atop the stack is the address following the copied instruction. * We need to make it the address following the original instruction. * * If this is the first time we've single-stepped the instruction at * this probepoint, and the instruction is boostable, boost it: add a * jump instruction after the copied instruction, that jumps to the next * instruction after the probepoint. */ static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { unsigned long *tos = stack_addr(regs); unsigned long copy_ip = (unsigned long)p->ainsn.insn; unsigned long orig_ip = (unsigned long)p->addr; kprobe_opcode_t *insn = p->ainsn.insn; /* Skip prefixes */ insn = skip_prefixes(insn); regs->flags &= ~X86_EFLAGS_TF; switch (*insn) { case 0x9c: /* pushfl */ *tos &= ~(X86_EFLAGS_TF | X86_EFLAGS_IF); *tos |= kcb->kprobe_old_flags; break; case 0xc2: /* iret/ret/lret */ case 0xc3: case 0xca: case 0xcb: case 0xcf: case 0xea: /* jmp absolute -- ip is correct */ /* ip is already adjusted, no more changes required */ p->ainsn.boostable = 1; goto no_change; case 0xe8: /* call relative - Fix return addr */ *tos = orig_ip + (*tos - copy_ip); break; #ifdef CONFIG_X86_32 case 0x9a: /* call absolute -- same as call absolute, indirect */ *tos = orig_ip + (*tos - copy_ip); goto no_change; #endif case 0xff: if ((insn[1] & 0x30) == 0x10) { /* * call absolute, indirect * Fix return addr; ip is correct. * But this is not boostable */ *tos = orig_ip + (*tos - copy_ip); goto no_change; } else if (((insn[1] & 0x31) == 0x20) || ((insn[1] & 0x31) == 0x21)) { /* * jmp near and far, absolute indirect * ip is correct. And this is boostable */ p->ainsn.boostable = 1; goto no_change; } default: break; } if (p->ainsn.boostable == 0) { if ((regs->ip > copy_ip) && (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) { /* * These instructions can be executed directly if it * jumps back to correct address. */ synthesize_reljump((void *)regs->ip, (void *)orig_ip + (regs->ip - copy_ip)); p->ainsn.boostable = 1; } else { p->ainsn.boostable = -1; } } regs->ip += orig_ip - copy_ip; no_change: restore_btf(); } /* * Interrupts are disabled on entry as trap1 is an interrupt gate and they * remain disabled throughout this function. */ static int __kprobes post_kprobe_handler(struct pt_regs *regs) { struct kprobe *cur = kprobe_running(); struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); if (!cur) return 0; resume_execution(cur, regs, kcb); regs->flags |= kcb->kprobe_saved_flags; if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) { kcb->kprobe_status = KPROBE_HIT_SSDONE; cur->post_handler(cur, regs, 0); } /* 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, flags * will have TF set, in which case, continue the remaining processing * of do_debug, as if this is not a probe hit. */ if (regs->flags & X86_EFLAGS_TF) return 0; return 1; } int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr) { struct kprobe *cur = kprobe_running(); struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); if (unlikely(regs->ip == (unsigned long)cur->ainsn.insn)) { /* This must happen on single-stepping */ WARN_ON(kcb->kprobe_status != KPROBE_HIT_SS && kcb->kprobe_status != KPROBE_REENTER); /* * We are here because the instruction being single * stepped caused a page fault. We reset the current * kprobe and the ip points back to the probe address * and allow the page fault handler to continue as a * normal page fault. */ regs->ip = (unsigned long)cur->addr; regs->flags |= kcb->kprobe_old_flags; if (kcb->kprobe_status == KPROBE_REENTER) restore_previous_kprobe(kcb); else reset_current_kprobe(); preempt_enable_no_resched(); } else if (kcb->kprobe_status == KPROBE_HIT_ACTIVE || kcb->kprobe_status == KPROBE_HIT_SSDONE) { /* * We increment the nmissed count for accounting, * we can also use npre/npostfault count for accounting * these specific fault cases. */ kprobes_inc_nmissed_count(cur); /* * We come here because instructions in the pre/post * handler caused the page_fault, this could happen * if handler tries to access user space by * copy_from_user(), get_user() etc. Let the * user-specified handler try to fix it first. */ if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr)) return 1; /* * In case the user-specified fault handler returned * zero, try to fix up. */ if (fixup_exception(regs)) return 1; /* * fixup routine could not handle it, * Let do_page_fault() fix it. */ } return 0; } /* * Wrapper routine for handling exceptions. */ int __kprobes kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *data) { struct die_args *args = data; int ret = NOTIFY_DONE; if (args->regs && user_mode_vm(args->regs)) return ret; switch (val) { case DIE_INT3: if (kprobe_handler(args->regs)) ret = NOTIFY_STOP; break; case DIE_DEBUG: if (post_kprobe_handler(args->regs)) { /* * Reset the BS bit in dr6 (pointed by args->err) to * denote completion of processing */ (*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP; ret = NOTIFY_STOP; } break; case DIE_GPF: /* * To be potentially processing a kprobe fault and to * trust the result from kprobe_running(), we have * be non-preemptible. */ if (!preemptible() && kprobe_running() && kprobe_fault_handler(args->regs, args->trapnr)) ret = NOTIFY_STOP; break; default: break; } return ret; } int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs) { struct jprobe *jp = container_of(p, struct jprobe, kp); unsigned long addr; struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); kcb->jprobe_saved_regs = *regs; kcb->jprobe_saved_sp = stack_addr(regs); addr = (unsigned long)(kcb->jprobe_saved_sp); /* * As Linus pointed out, gcc assumes that the callee * owns the argument space and could overwrite it, e.g. * tailcall optimization. So, to be absolutely safe * we also save and restore enough stack bytes to cover * the argument area. */ memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr, MIN_STACK_SIZE(addr)); regs->flags &= ~X86_EFLAGS_IF; trace_hardirqs_off(); regs->ip = (unsigned long)(jp->entry); return 1; } void __kprobes jprobe_return(void) { struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); asm volatile ( #ifdef CONFIG_X86_64 " xchg %%rbx,%%rsp \n" #else " xchgl %%ebx,%%esp \n" #endif " int3 \n" " .globl jprobe_return_end\n" " jprobe_return_end: \n" " nop \n"::"b" (kcb->jprobe_saved_sp):"memory"); } int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) { struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); u8 *addr = (u8 *) (regs->ip - 1); struct jprobe *jp = container_of(p, struct jprobe, kp); if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) { if (stack_addr(regs) != kcb->jprobe_saved_sp) { struct pt_regs *saved_regs = &kcb->jprobe_saved_regs; printk(KERN_ERR "current sp %p does not match saved sp %p\n", stack_addr(regs), kcb->jprobe_saved_sp); printk(KERN_ERR "Saved registers for jprobe %p\n", jp); show_regs(saved_regs); printk(KERN_ERR "Current registers\n"); show_regs(regs); BUG(); } *regs = kcb->jprobe_saved_regs; memcpy((kprobe_opcode_t *)(kcb->jprobe_saved_sp), kcb->jprobes_stack, MIN_STACK_SIZE(kcb->jprobe_saved_sp)); preempt_enable_no_resched(); return 1; } return 0; } int __init arch_init_kprobes(void) { return 0; } int __kprobes arch_trampoline_kprobe(struct kprobe *p) { return 0; }