/* * arch/arm/kernel/kprobes.c * * Kprobes on ARM * * Abhishek Sagar <sagar.abhishek@gmail.com> * Copyright (C) 2006, 2007 Motorola Inc. * * Nicolas Pitre <nico@marvell.com> * Copyright (C) 2007 Marvell Ltd. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. * * 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. */ #include <linux/kernel.h> #include <linux/kprobes.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/stop_machine.h> #include <linux/stringify.h> #include <asm/traps.h> #include <asm/cacheflush.h> #define MIN_STACK_SIZE(addr) \ min((unsigned long)MAX_STACK_SIZE, \ (unsigned long)current_thread_info() + THREAD_START_SP - (addr)) #define flush_insns(addr, cnt) \ flush_icache_range((unsigned long)(addr), \ (unsigned long)(addr) + \ sizeof(kprobe_opcode_t) * (cnt)) /* Used as a marker in ARM_pc to note when we're in a jprobe. */ #define JPROBE_MAGIC_ADDR 0xffffffff DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL; DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk); int __kprobes arch_prepare_kprobe(struct kprobe *p) { kprobe_opcode_t insn; kprobe_opcode_t tmp_insn[MAX_INSN_SIZE]; unsigned long addr = (unsigned long)p->addr; int is; if (addr & 0x3 || in_exception_text(addr)) return -EINVAL; insn = *p->addr; p->opcode = insn; p->ainsn.insn = tmp_insn; switch (arm_kprobe_decode_insn(insn, &p->ainsn)) { case INSN_REJECTED: /* not supported */ return -EINVAL; case INSN_GOOD: /* instruction uses slot */ p->ainsn.insn = get_insn_slot(); if (!p->ainsn.insn) return -ENOMEM; for (is = 0; is < MAX_INSN_SIZE; ++is) p->ainsn.insn[is] = tmp_insn[is]; flush_insns(p->ainsn.insn, MAX_INSN_SIZE); break; case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */ p->ainsn.insn = NULL; break; } return 0; } void __kprobes arch_arm_kprobe(struct kprobe *p) { *p->addr = KPROBE_BREAKPOINT_INSTRUCTION; flush_insns(p->addr, 1); } /* * The actual disarming is done here on each CPU and synchronized using * stop_machine. This synchronization is necessary on SMP to avoid removing * a probe between the moment the 'Undefined Instruction' exception is raised * and the moment the exception handler reads the faulting instruction from * memory. */ int __kprobes __arch_disarm_kprobe(void *p) { struct kprobe *kp = p; *kp->addr = kp->opcode; flush_insns(kp->addr, 1); return 0; } void __kprobes arch_disarm_kprobe(struct kprobe *p) { stop_machine(__arch_disarm_kprobe, p, &cpu_online_map); } void __kprobes arch_remove_kprobe(struct kprobe *p) { if (p->ainsn.insn) { free_insn_slot(p->ainsn.insn, 0); 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; } static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb) { __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp; kcb->kprobe_status = kcb->prev_kprobe.status; } static void __kprobes set_current_kprobe(struct kprobe *p) { __get_cpu_var(current_kprobe) = p; } static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb) { regs->ARM_pc += 4; p->ainsn.insn_handler(p, regs); } /* * Called with IRQs disabled. IRQs must remain disabled from that point * all the way until processing this kprobe is complete. The current * kprobes implementation cannot process more than one nested level of * kprobe, and that level is reserved for user kprobe handlers, so we can't * risk encountering a new kprobe in an interrupt handler. */ void __kprobes kprobe_handler(struct pt_regs *regs) { struct kprobe *p, *cur; struct kprobe_ctlblk *kcb; kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->ARM_pc; kcb = get_kprobe_ctlblk(); cur = kprobe_running(); p = get_kprobe(addr); if (p) { if (cur) { /* Kprobe is pending, so we're recursing. */ switch (kcb->kprobe_status) { case KPROBE_HIT_ACTIVE: case KPROBE_HIT_SSDONE: /* A pre- or post-handler probe got us here. */ kprobes_inc_nmissed_count(p); save_previous_kprobe(kcb); set_current_kprobe(p); kcb->kprobe_status = KPROBE_REENTER; singlestep(p, regs, kcb); restore_previous_kprobe(kcb); break; default: /* impossible cases */ BUG(); } } else { set_current_kprobe(p); 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, * so get out doing nothing more here. */ if (!p->pre_handler || !p->pre_handler(p, regs)) { kcb->kprobe_status = KPROBE_HIT_SS; singlestep(p, regs, kcb); if (p->post_handler) { kcb->kprobe_status = KPROBE_HIT_SSDONE; p->post_handler(p, regs, 0); } reset_current_kprobe(); } } } else if (cur) { /* We probably hit a jprobe. Call its break handler. */ if (cur->break_handler && cur->break_handler(cur, regs)) { kcb->kprobe_status = KPROBE_HIT_SS; singlestep(cur, regs, kcb); if (cur->post_handler) { kcb->kprobe_status = KPROBE_HIT_SSDONE; cur->post_handler(cur, regs, 0); } } reset_current_kprobe(); } else { /* * The probe was removed and a race is in progress. * There is nothing we can do about it. Let's restart * the instruction. By the time we can restart, the * real instruction will be there. */ } } static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr) { unsigned long flags; local_irq_save(flags); kprobe_handler(regs); local_irq_restore(flags); return 0; } int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr) { struct kprobe *cur = kprobe_running(); struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); 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 PC to point back to the probe address * and allow the page fault handler to continue as a * normal page fault. */ regs->ARM_pc = (long)cur->addr; if (kcb->kprobe_status == KPROBE_REENTER) { restore_previous_kprobe(kcb); } else { reset_current_kprobe(); } break; case KPROBE_HIT_ACTIVE: case 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. */ if (cur->fault_handler && cur->fault_handler(cur, regs, fsr)) return 1; break; default: break; } return 0; } int __kprobes kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *data) { /* * notify_die() is currently never called on ARM, * so this callback is currently empty. */ return NOTIFY_DONE; } /* * When a retprobed function returns, trampoline_handler() is called, * calling the kretprobe's handler. We construct a struct pt_regs to * give a view of registers r0-r11 to the user return-handler. This is * not a complete pt_regs structure, but that should be plenty sufficient * for kretprobe handlers which should normally be interested in r0 only * anyway. */ void __naked __kprobes kretprobe_trampoline(void) { __asm__ __volatile__ ( "stmdb sp!, {r0 - r11} \n\t" "mov r0, sp \n\t" "bl trampoline_handler \n\t" "mov lr, r0 \n\t" "ldmia sp!, {r0 - r11} \n\t" "mov pc, lr \n\t" : : : "memory"); } /* Called from kretprobe_trampoline */ static __used __kprobes void *trampoline_handler(struct pt_regs *regs) { struct kretprobe_instance *ri = NULL; struct hlist_head *head, empty_rp; struct hlist_node *node, *tmp; unsigned long flags, orig_ret_address = 0; unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline; INIT_HLIST_HEAD(&empty_rp); kretprobe_hash_lock(current, &head, &flags); /* * It is possible to have multiple instances associated with a given * task either because multiple functions in the call path have * a return probe installed on them, and/or more than one 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) { __get_cpu_var(current_kprobe) = &ri->rp->kp; get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; ri->rp->handler(ri, regs); __get_cpu_var(current_kprobe) = NULL; } orig_ret_address = (unsigned long)ri->ret_addr; 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_assert(ri, orig_ret_address, trampoline_address); kretprobe_hash_unlock(current, &flags); hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) { hlist_del(&ri->hlist); kfree(ri); } return (void *)orig_ret_address; } void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs) { ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr; /* Replace the return addr with trampoline addr. */ regs->ARM_lr = (unsigned long)&kretprobe_trampoline; } int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs) { struct jprobe *jp = container_of(p, struct jprobe, kp); struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); long sp_addr = regs->ARM_sp; kcb->jprobe_saved_regs = *regs; memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr)); regs->ARM_pc = (long)jp->entry; regs->ARM_cpsr |= PSR_I_BIT; preempt_disable(); return 1; } void __kprobes jprobe_return(void) { struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); __asm__ __volatile__ ( /* * Setup an empty pt_regs. Fill SP and PC fields as * they're needed by longjmp_break_handler. * * We allocate some slack between the original SP and start of * our fabricated regs. To be precise we want to have worst case * covered which is STMFD with all 16 regs so we allocate 2 * * sizeof(struct_pt_regs)). * * This is to prevent any simulated instruction from writing * over the regs when they are accessing the stack. */ "sub sp, %0, %1 \n\t" "ldr r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t" "str %0, [sp, %2] \n\t" "str r0, [sp, %3] \n\t" "mov r0, sp \n\t" "bl kprobe_handler \n\t" /* * Return to the context saved by setjmp_pre_handler * and restored by longjmp_break_handler. */ "ldr r0, [sp, %4] \n\t" "msr cpsr_cxsf, r0 \n\t" "ldmia sp, {r0 - pc} \n\t" : : "r" (kcb->jprobe_saved_regs.ARM_sp), "I" (sizeof(struct pt_regs) * 2), "J" (offsetof(struct pt_regs, ARM_sp)), "J" (offsetof(struct pt_regs, ARM_pc)), "J" (offsetof(struct pt_regs, ARM_cpsr)) : "memory", "cc"); } int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) { struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); long stack_addr = kcb->jprobe_saved_regs.ARM_sp; long orig_sp = regs->ARM_sp; struct jprobe *jp = container_of(p, struct jprobe, kp); if (regs->ARM_pc == JPROBE_MAGIC_ADDR) { if (orig_sp != stack_addr) { struct pt_regs *saved_regs = (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp; printk("current sp %lx does not match saved sp %lx\n", orig_sp, stack_addr); printk("Saved registers for jprobe %p\n", jp); show_regs(saved_regs); printk("Current registers\n"); show_regs(regs); BUG(); } *regs = kcb->jprobe_saved_regs; memcpy((void *)stack_addr, kcb->jprobes_stack, MIN_STACK_SIZE(stack_addr)); preempt_enable_no_resched(); return 1; } return 0; } int __kprobes arch_trampoline_kprobe(struct kprobe *p) { return 0; } static struct undef_hook kprobes_break_hook = { .instr_mask = 0xffffffff, .instr_val = KPROBE_BREAKPOINT_INSTRUCTION, .cpsr_mask = MODE_MASK, .cpsr_val = SVC_MODE, .fn = kprobe_trap_handler, }; int __init arch_init_kprobes() { arm_kprobe_decode_init(); register_undef_hook(&kprobes_break_hook); return 0; }