| Message ID | 1416292375-29560-4-git-send-email-dave.long@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 11/18/2014 01:32 AM, David Long wrote: > From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org> > > AArch64 ISA does not instructions to pop PC register value > from stack(like ARM v7 has ldmia {...,pc}) without using > one of the general purpose registers. This means return probes > cannot return to the actual return address directly without > modifying register context, and without trapping into debug exception. The first might read better with something like: Unlike the ARMv7 (ldmia {...,pc}) the AArch64 ISA cannot directly pop the PC register value from the stack without using one of the general purpose registers. -Will > > So like many other architectures, we prepare a global routine > with NOPs, which serve as trampoline to hack away the > function return address, by placing an extra kprobe on the > trampoline entry. > > The pre-handler of this special trampoline' kprobe execute return > probe handler functions and restore original return address in ELR_EL1, > this way, saved pt_regs still hold the original register context to be > carried back to the probed kernel function. > > Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org> > Signed-off-by: David A. Long <dave.long@linaro.org> > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/kprobes.h | 1 + > arch/arm64/kernel/kprobes.c | 114 ++++++++++++++++++++++++++++++++++++++- > 3 files changed, 115 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 256ef90..02f31b7 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -61,6 +61,7 @@ config ARM64 > select HAVE_RCU_TABLE_FREE > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES if !XIP_KERNEL > + select HAVE_KRETPROBES if HAVE_KPROBES > select IRQ_DOMAIN > select MODULES_USE_ELF_RELA > select NO_BOOTMEM > diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h > index b35d3b9..a2de3b8 100644 > --- a/arch/arm64/include/asm/kprobes.h > +++ b/arch/arm64/include/asm/kprobes.h > @@ -56,5 +56,6 @@ void arch_remove_kprobe(struct kprobe *); > int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr); > int kprobe_exceptions_notify(struct notifier_block *self, > unsigned long val, void *data); > +void kretprobe_trampoline(void); > > #endif /* _ARM_KPROBES_H */ > diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c > index 789ab61..be7c330 100644 > --- a/arch/arm64/kernel/kprobes.c > +++ b/arch/arm64/kernel/kprobes.c > @@ -569,6 +569,117 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) > return 0; > } > > +/* > + * Kretprobes: kernel return probes handling > + * > + * AArch64 mode does not support popping the PC value from the > + * stack like on ARM 32-bit (ldmia {..,pc}), so atleast one > + * register need to be used to achieve branching/return. > + * It means return probes cannot return back to the original > + * return address directly without modifying the register context. > + * > + * So like other architectures, we prepare a global routine > + * with NOPs, which serve as trampoline address that hack away the > + * function return, with the exact register context. > + * Placing a kprobe on trampoline routine entry will trap again to > + * execute return probe handlers and restore original return address > + * in ELR_EL1, this way saved pt_regs still hold the original > + * register values to be carried back to the caller. > + */ > +static void __used kretprobe_trampoline_holder(void) > +{ > + asm volatile (".global kretprobe_trampoline\n" > + "kretprobe_trampoline:\n" > + "NOP\n\t" > + "NOP\n\t"); > +} > + > +static int __kprobes > +trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) > +{ > + struct kretprobe_instance *ri = NULL; > + struct hlist_head *head, empty_rp; > + struct hlist_node *tmp; > + unsigned long flags, orig_ret_addr = 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, tmp, head, hlist) { > + if (ri->task != current) > + /* another task is sharing our hash bucket */ > + continue; > + > + if (ri->rp && ri->rp->handler) { > + __this_cpu_write(current_kprobe, &ri->rp->kp); > + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; > + ri->rp->handler(ri, regs); > + __this_cpu_write(current_kprobe, NULL); > + } > + > + orig_ret_addr = (unsigned long)ri->ret_addr; > + recycle_rp_inst(ri, &empty_rp); > + > + if (orig_ret_addr != 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_addr, trampoline_address); > + /* restore the original return address */ > + instruction_pointer(regs) = orig_ret_addr; > + reset_current_kprobe(); > + kretprobe_hash_unlock(current, &flags); > + > + hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) { > + hlist_del(&ri->hlist); > + kfree(ri); > + } > + > + kprobes_restore_local_irqflag(regs); > + > + /* return 1 so that post handlers not called */ > + return 1; > +} > + > +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri, > + struct pt_regs *regs) > +{ > + ri->ret_addr = (kprobe_opcode_t *)regs->regs[30]; > + > + /* replace return addr (x30) with trampoline */ > + regs->regs[30] = (long)&kretprobe_trampoline; > +} > + > +static struct kprobe trampoline = { > + .addr = (kprobe_opcode_t *) &kretprobe_trampoline, > + .pre_handler = trampoline_probe_handler > +}; > + > +int __kprobes arch_trampoline_kprobe(struct kprobe *p) > +{ > + return p->addr == (kprobe_opcode_t *) &kretprobe_trampoline; > +} > + > /* Break Handler hook */ > static struct break_hook kprobes_break_hook = { > .esr_mask = BRK64_ESR_MASK, > @@ -586,5 +697,6 @@ int __init arch_init_kprobes(void) > register_break_hook(&kprobes_break_hook); > register_step_hook(&kprobes_step_hook); > > - return 0; > + /* register trampoline for kret probe */ > + return register_kprobe(&trampoline); > } >
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 256ef90..02f31b7 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -61,6 +61,7 @@ config ARM64 select HAVE_RCU_TABLE_FREE select HAVE_SYSCALL_TRACEPOINTS select HAVE_KPROBES if !XIP_KERNEL + select HAVE_KRETPROBES if HAVE_KPROBES select IRQ_DOMAIN select MODULES_USE_ELF_RELA select NO_BOOTMEM diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h index b35d3b9..a2de3b8 100644 --- a/arch/arm64/include/asm/kprobes.h +++ b/arch/arm64/include/asm/kprobes.h @@ -56,5 +56,6 @@ void arch_remove_kprobe(struct kprobe *); int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr); int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *data); +void kretprobe_trampoline(void); #endif /* _ARM_KPROBES_H */ diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c index 789ab61..be7c330 100644 --- a/arch/arm64/kernel/kprobes.c +++ b/arch/arm64/kernel/kprobes.c @@ -569,6 +569,117 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) return 0; } +/* + * Kretprobes: kernel return probes handling + * + * AArch64 mode does not support popping the PC value from the + * stack like on ARM 32-bit (ldmia {..,pc}), so atleast one + * register need to be used to achieve branching/return. + * It means return probes cannot return back to the original + * return address directly without modifying the register context. + * + * So like other architectures, we prepare a global routine + * with NOPs, which serve as trampoline address that hack away the + * function return, with the exact register context. + * Placing a kprobe on trampoline routine entry will trap again to + * execute return probe handlers and restore original return address + * in ELR_EL1, this way saved pt_regs still hold the original + * register values to be carried back to the caller. + */ +static void __used kretprobe_trampoline_holder(void) +{ + asm volatile (".global kretprobe_trampoline\n" + "kretprobe_trampoline:\n" + "NOP\n\t" + "NOP\n\t"); +} + +static int __kprobes +trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) +{ + struct kretprobe_instance *ri = NULL; + struct hlist_head *head, empty_rp; + struct hlist_node *tmp; + unsigned long flags, orig_ret_addr = 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, tmp, head, hlist) { + if (ri->task != current) + /* another task is sharing our hash bucket */ + continue; + + if (ri->rp && ri->rp->handler) { + __this_cpu_write(current_kprobe, &ri->rp->kp); + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE; + ri->rp->handler(ri, regs); + __this_cpu_write(current_kprobe, NULL); + } + + orig_ret_addr = (unsigned long)ri->ret_addr; + recycle_rp_inst(ri, &empty_rp); + + if (orig_ret_addr != 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_addr, trampoline_address); + /* restore the original return address */ + instruction_pointer(regs) = orig_ret_addr; + reset_current_kprobe(); + kretprobe_hash_unlock(current, &flags); + + hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) { + hlist_del(&ri->hlist); + kfree(ri); + } + + kprobes_restore_local_irqflag(regs); + + /* return 1 so that post handlers not called */ + return 1; +} + +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri, + struct pt_regs *regs) +{ + ri->ret_addr = (kprobe_opcode_t *)regs->regs[30]; + + /* replace return addr (x30) with trampoline */ + regs->regs[30] = (long)&kretprobe_trampoline; +} + +static struct kprobe trampoline = { + .addr = (kprobe_opcode_t *) &kretprobe_trampoline, + .pre_handler = trampoline_probe_handler +}; + +int __kprobes arch_trampoline_kprobe(struct kprobe *p) +{ + return p->addr == (kprobe_opcode_t *) &kretprobe_trampoline; +} + /* Break Handler hook */ static struct break_hook kprobes_break_hook = { .esr_mask = BRK64_ESR_MASK, @@ -586,5 +697,6 @@ int __init arch_init_kprobes(void) register_break_hook(&kprobes_break_hook); register_step_hook(&kprobes_step_hook); - return 0; + /* register trampoline for kret probe */ + return register_kprobe(&trampoline); }