/* * Kernel Probes (KProbes) * arch/i386/kernel/kprobes.c * * 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. * 2005-May Hien Nguyen , Jim Keniston * and Prasanna S Panchamukhi * added function-return probes. */ #include #include #include #include #include #include #include #include static struct kprobe *current_kprobe; static unsigned long kprobe_status, kprobe_old_eflags, kprobe_saved_eflags; static struct kprobe *kprobe_prev; static unsigned long kprobe_status_prev, kprobe_old_eflags_prev, kprobe_saved_eflags_prev; static struct pt_regs jprobe_saved_regs; static long *jprobe_saved_esp; /* copy of the kernel stack at the probe fire time */ static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE]; void jprobe_return_end(void); /* * returns non-zero if opcode modifies the interrupt flag. */ static inline int is_IF_modifier(kprobe_opcode_t opcode) { switch (opcode) { case 0xfa: /* cli */ case 0xfb: /* sti */ case 0xcf: /* iret/iretd */ case 0x9d: /* popf/popfd */ return 1; } return 0; } int __kprobes arch_prepare_kprobe(struct kprobe *p) { return 0; } void __kprobes arch_copy_kprobe(struct kprobe *p) { memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t)); p->opcode = *p->addr; } void __kprobes arch_arm_kprobe(struct kprobe *p) { *p->addr = BREAKPOINT_INSTRUCTION; flush_icache_range((unsigned long) p->addr, (unsigned long) p->addr + sizeof(kprobe_opcode_t)); } void __kprobes arch_disarm_kprobe(struct kprobe *p) { *p->addr = p->opcode; flush_icache_range((unsigned long) p->addr, (unsigned long) p->addr + sizeof(kprobe_opcode_t)); } void __kprobes arch_remove_kprobe(struct kprobe *p) { } static inline void save_previous_kprobe(void) { kprobe_prev = current_kprobe; kprobe_status_prev = kprobe_status; kprobe_old_eflags_prev = kprobe_old_eflags; kprobe_saved_eflags_prev = kprobe_saved_eflags; } static inline void restore_previous_kprobe(void) { current_kprobe = kprobe_prev; kprobe_status = kprobe_status_prev; kprobe_old_eflags = kprobe_old_eflags_prev; kprobe_saved_eflags = kprobe_saved_eflags_prev; } static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs) { current_kprobe = p; kprobe_saved_eflags = kprobe_old_eflags = (regs->eflags & (TF_MASK | IF_MASK)); if (is_IF_modifier(p->opcode)) kprobe_saved_eflags &= ~IF_MASK; } static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs) { regs->eflags |= TF_MASK; regs->eflags &= ~IF_MASK; /*single step inline if the instruction is an int3*/ if (p->opcode == BREAKPOINT_INSTRUCTION) regs->eip = (unsigned long)p->addr; else regs->eip = (unsigned long)&p->ainsn.insn; } void __kprobes arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs) { unsigned long *sara = (unsigned long *)®s->esp; struct kretprobe_instance *ri; if ((ri = get_free_rp_inst(rp)) != NULL) { ri->rp = rp; ri->task = current; ri->ret_addr = (kprobe_opcode_t *) *sara; /* Replace the return addr with trampoline addr */ *sara = (unsigned long) &kretprobe_trampoline; add_rp_inst(ri); } else { rp->nmissed++; } } /* * Interrupts are disabled on entry as trap3 is an interrupt gate and they * remain disabled thorough out this function. */ static int __kprobes kprobe_handler(struct pt_regs *regs) { struct kprobe *p; int ret = 0; kprobe_opcode_t *addr = NULL; unsigned long *lp; /* We're in an interrupt, but this is clear and BUG()-safe. */ preempt_disable(); /* Check if the application is using LDT entry for its code segment and * calculate the address by reading the base address from the LDT entry. */ if ((regs->xcs & 4) && (current->mm)) { lp = (unsigned long *) ((unsigned long)((regs->xcs >> 3) * 8) + (char *) current->mm->context.ldt); addr = (kprobe_opcode_t *) (get_desc_base(lp) + regs->eip - sizeof(kprobe_opcode_t)); } else { addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t)); } /* Check we're not actually recursing */ if (kprobe_running()) { /* We *are* holding lock here, so this is safe. Disarm the probe we just hit, and ignore it. */ p = get_kprobe(addr); if (p) { if (kprobe_status == KPROBE_HIT_SS && *p->ainsn.insn == BREAKPOINT_INSTRUCTION) { regs->eflags &= ~TF_MASK; regs->eflags |= kprobe_saved_eflags; unlock_kprobes(); 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(); set_current_kprobe(p, regs); p->nmissed++; prepare_singlestep(p, regs); kprobe_status = KPROBE_REENTER; return 1; } else { p = current_kprobe; if (p->break_handler && p->break_handler(p, regs)) { goto ss_probe; } } /* If it's not ours, can't be delete race, (we hold lock). */ goto no_kprobe; } lock_kprobes(); p = get_kprobe(addr); if (!p) { unlock_kprobes(); if (regs->eflags & VM_MASK) { /* We are in virtual-8086 mode. Return 0 */ goto no_kprobe; } 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->eip -= sizeof(kprobe_opcode_t); ret = 1; } /* Not one of ours: let kernel handle it */ goto no_kprobe; } kprobe_status = KPROBE_HIT_ACTIVE; set_current_kprobe(p, regs); if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; ss_probe: prepare_singlestep(p, regs); kprobe_status = KPROBE_HIT_SS; return 1; no_kprobe: preempt_enable_no_resched(); return ret; } /* * For function-return probes, init_kprobes() establishes a probepoint * here. When a retprobed function returns, this probe is hit and * trampoline_probe_handler() runs, calling the kretprobe's handler. */ void kretprobe_trampoline_holder(void) { asm volatile ( ".global kretprobe_trampoline\n" "kretprobe_trampoline: \n" "nop\n"); } /* * Called when we hit the probe point at kretprobe_trampoline */ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) { struct kretprobe_instance *ri = NULL; struct hlist_head *head; struct hlist_node *node, *tmp; unsigned long orig_ret_address = 0; unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline; head = kretprobe_inst_table_head(current); /* * It is possible to have multiple instances associated with a given * task either because an multiple functions in the call path * have a return probe installed on them, and/or more then one return * return probe was registered for a target function. * * We can handle this because: * - instances are always inserted at the head of the list * - when multiple return probes are registered for the same * function, the first instance's ret_addr will point to the * real return address, and all the rest will point to * kretprobe_trampoline */ hlist_for_each_entry_safe(ri, node, tmp, head, hlist) { if (ri->task != current) /* another task is sharing our hash bucket */ continue; if (ri->rp && ri->rp->handler) ri->rp->handler(ri, regs); orig_ret_address = (unsigned long)ri->ret_addr; recycle_rp_inst(ri); 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; } BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address)); regs->eip = orig_ret_address; unlock_kprobes(); preempt_enable_no_resched(); /* * By returning a non-zero value, we are telling * kprobe_handler() that we have handled unlocking * and re-enabling preemption. */ return 1; } /* * 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 eip 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 eflags, 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. */ static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs) { unsigned long *tos = (unsigned long *)®s->esp; unsigned long next_eip = 0; unsigned long copy_eip = (unsigned long)&p->ainsn.insn; unsigned long orig_eip = (unsigned long)p->addr; switch (p->ainsn.insn[0]) { case 0x9c: /* pushfl */ *tos &= ~(TF_MASK | IF_MASK); *tos |= kprobe_old_eflags; break; case 0xc3: /* ret/lret */ case 0xcb: case 0xc2: case 0xca: regs->eflags &= ~TF_MASK; /* eip is already adjusted, no more changes required*/ return; case 0xe8: /* call relative - Fix return addr */ *tos = orig_eip + (*tos - copy_eip); break; case 0xff: if ((p->ainsn.insn[1] & 0x30) == 0x10) { /* call absolute, indirect */ /* Fix return addr; eip is correct. */ next_eip = regs->eip; *tos = orig_eip + (*tos - copy_eip); } else if (((p->ainsn.insn[1] & 0x31) == 0x20) || /* jmp near, absolute indirect */ ((p->ainsn.insn[1] & 0x31) == 0x21)) { /* jmp far, absolute indirect */ /* eip is correct. */ next_eip = regs->eip; } break; case 0xea: /* jmp absolute -- eip is correct */ next_eip = regs->eip; break; default: break; } regs->eflags &= ~TF_MASK; if (next_eip) { regs->eip = next_eip; } else { regs->eip = orig_eip + (regs->eip - copy_eip); } } /* * Interrupts are disabled on entry as trap1 is an interrupt gate and they * remain disabled thoroughout this function. And we hold kprobe lock. */ static inline int post_kprobe_handler(struct pt_regs *regs) { if (!kprobe_running()) return 0; if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) { kprobe_status = KPROBE_HIT_SSDONE; current_kprobe->post_handler(current_kprobe, regs, 0); } resume_execution(current_kprobe, regs); regs->eflags |= kprobe_saved_eflags; /*Restore back the original saved kprobes variables and continue. */ if (kprobe_status == KPROBE_REENTER) { restore_previous_kprobe(); goto out; } unlock_kprobes(); out: preempt_enable_no_resched(); /* * if somebody else is singlestepping across a probe point, eflags * will have TF set, in which case, continue the remaining processing * of do_debug, as if this is not a probe hit. */ if (regs->eflags & TF_MASK) return 0; return 1; } /* Interrupts disabled, kprobe_lock held. */ static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr) { if (current_kprobe->fault_handler && current_kprobe->fault_handler(current_kprobe, regs, trapnr)) return 1; if (kprobe_status & KPROBE_HIT_SS) { resume_execution(current_kprobe, regs); regs->eflags |= kprobe_old_eflags; unlock_kprobes(); preempt_enable_no_resched(); } return 0; } /* * Wrapper routine to for handling exceptions. */ int __kprobes kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *data) { struct die_args *args = (struct die_args *)data; switch (val) { case DIE_INT3: if (kprobe_handler(args->regs)) return NOTIFY_STOP; break; case DIE_DEBUG: if (post_kprobe_handler(args->regs)) return NOTIFY_STOP; break; case DIE_GPF: if (kprobe_running() && kprobe_fault_handler(args->regs, args->trapnr)) return NOTIFY_STOP; break; case DIE_PAGE_FAULT: if (kprobe_running() && kprobe_fault_handler(args->regs, args->trapnr)) return NOTIFY_STOP; break; default: break; } return NOTIFY_DONE; } int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs) { struct jprobe *jp = container_of(p, struct jprobe, kp); unsigned long addr; jprobe_saved_regs = *regs; jprobe_saved_esp = ®s->esp; addr = (unsigned long)jprobe_saved_esp; /* * TBD: 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(jprobes_stack, (kprobe_opcode_t *) addr, MIN_STACK_SIZE(addr)); regs->eflags &= ~IF_MASK; regs->eip = (unsigned long)(jp->entry); return 1; } void __kprobes jprobe_return(void) { preempt_enable_no_resched(); asm volatile (" xchgl %%ebx,%%esp \n" " int3 \n" " .globl jprobe_return_end \n" " jprobe_return_end: \n" " nop \n"::"b" (jprobe_saved_esp):"memory"); } int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) { u8 *addr = (u8 *) (regs->eip - 1); unsigned long stack_addr = (unsigned long)jprobe_saved_esp; struct jprobe *jp = container_of(p, struct jprobe, kp); if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) { if (®s->esp != jprobe_saved_esp) { struct pt_regs *saved_regs = container_of(jprobe_saved_esp, struct pt_regs, esp); printk("current esp %p does not match saved esp %p\n", ®s->esp, jprobe_saved_esp); printk("Saved registers for jprobe %p\n", jp); show_registers(saved_regs); printk("Current registers\n"); show_registers(regs); BUG(); } *regs = jprobe_saved_regs; memcpy((kprobe_opcode_t *) stack_addr, jprobes_stack, MIN_STACK_SIZE(stack_addr)); return 1; } return 0; } 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); }