Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751840AbbBSOtl (ORCPT ); Thu, 19 Feb 2015 09:49:41 -0500 Received: from mail7.hitachi.co.jp ([133.145.228.42]:37590 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751402AbbBSOtk (ORCPT ); Thu, 19 Feb 2015 09:49:40 -0500 Message-ID: <54E5F7FE.7050308@hitachi.com> Date: Thu, 19 Feb 2015 23:49:34 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: David Long Cc: linux-arm-kernel@lists.infradead.org, Russell King , Sandeepa Prabhu , William Cohen , Steve Capper , Catalin Marinas , Will Deacon , "Jon Medhurst (Tixy)" , Ananth N Mavinakayanahalli , Anil S Keshavamurthy , davem@davemloft.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 5/6] arm64: Add kernel return probes support (kretprobes) References: <1424214701-4899-1-git-send-email-dave.long@linaro.org> <1424214701-4899-6-git-send-email-dave.long@linaro.org> In-Reply-To: <1424214701-4899-6-git-send-email-dave.long@linaro.org> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7117 Lines: 200 (2015/02/18 8:11), David Long wrote: > From: Sandeepa Prabhu > > AArch64 ISA does not have instructions to pop the PC register > value from the 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. > > So, like many other architectures, we prepare a global routine > with NOPs which serve as a 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 executes the return > probe handler functions and restores original return address in ELR_EL1. > This way the saved pt_regs still hold the original register context to be > carried back to the probed kernel function. Looks good to me. Acked-by: Masami Hiramatsu Thanks! > > Signed-off-by: Sandeepa Prabhu > Signed-off-by: David A. Long > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/kprobes.h | 1 + > arch/arm64/kernel/kprobes.c | 112 ++++++++++++++++++++++++++++++++++++++- > 3 files changed, 113 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 9ffa8b8..a5e50e9 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -68,6 +68,7 @@ config ARM64 > select HAVE_RCU_TABLE_FREE > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > + 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 e157877..fb869f4 100644 > --- a/arch/arm64/kernel/kprobes.c > +++ b/arch/arm64/kernel/kprobes.c > @@ -559,6 +559,115 @@ 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); > + } > + > + /* 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, > @@ -576,5 +685,6 @@ 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); > } > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/