Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753488AbbF2RZe (ORCPT ); Mon, 29 Jun 2015 13:25:34 -0400 Received: from mail-ie0-f179.google.com ([209.85.223.179]:36428 "EHLO mail-ie0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753363AbbF2RZ2 (ORCPT ); Mon, 29 Jun 2015 13:25:28 -0400 MIME-Version: 1.0 In-Reply-To: <1434395229-6654-6-git-send-email-dave.long@linaro.org> References: <1434395229-6654-1-git-send-email-dave.long@linaro.org> <1434395229-6654-6-git-send-email-dave.long@linaro.org> Date: Mon, 29 Jun 2015 18:25:28 +0100 Message-ID: Subject: Re: [PATCH v7 5/7] arm64: Add trampoline code for kretprobes From: Steve Capper To: David Long Cc: Catalin Marinas , Will Deacon , "linux-arm-kernel@lists.infradead.org" , Russell King , sandeepa.s.prabhu@gmail.com, William Cohen , "Jon Medhurst (Tixy)" , Masami Hiramatsu , Ananth N Mavinakayanahalli , Anil S Keshavamurthy , David Miller , Mark Brown , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6229 Lines: 149 On 15 June 2015 at 20:07, David Long wrote: > From: William Cohen > > The trampoline code is used by kretprobes to capture a return from a probed > function. This is done by saving the registers, calling the handler, and > restoring the registers. The code then returns to the roginal saved caller > return address. It is necessary to do this directly instead of using a > software breakpoint because the code used in processing that breakpoint > could itself be kprobe'd and cause a problematic reentry into the debug > exception handler. > > Signed-off-by: William Cohen > Signed-off-by: David A. Long > --- > arch/arm64/include/asm/kprobes.h | 1 + > arch/arm64/kernel/kprobes-arm64.h | 41 +++++++++++++++++++++++++++++++++++++++ > arch/arm64/kernel/kprobes.c | 26 +++++++++++++++++++++++++ > 3 files changed, 68 insertions(+) > > diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h > index af31c4d..d081f49 100644 > --- a/arch/arm64/include/asm/kprobes.h > +++ b/arch/arm64/include/asm/kprobes.h > @@ -58,5 +58,6 @@ int kprobe_exceptions_notify(struct notifier_block *self, > unsigned long val, void *data); > int kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr); > int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr); > +void kretprobe_trampoline(void); > > #endif /* _ARM_KPROBES_H */ > diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h > index ff8a55f..bdcfa62 100644 > --- a/arch/arm64/kernel/kprobes-arm64.h > +++ b/arch/arm64/kernel/kprobes-arm64.h > @@ -27,4 +27,45 @@ extern kprobes_pstate_check_t * const kprobe_condition_checks[16]; > enum kprobe_insn __kprobes > arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi); > > +#define SAVE_REGS_STRING\ > + " stp x0, x1, [sp, #16 * 0]\n" \ > + " stp x2, x3, [sp, #16 * 1]\n" \ > + " stp x4, x5, [sp, #16 * 2]\n" \ > + " stp x6, x7, [sp, #16 * 3]\n" \ > + " stp x8, x9, [sp, #16 * 4]\n" \ > + " stp x10, x11, [sp, #16 * 5]\n" \ > + " stp x12, x13, [sp, #16 * 6]\n" \ > + " stp x14, x15, [sp, #16 * 7]\n" \ > + " stp x16, x17, [sp, #16 * 8]\n" \ > + " stp x18, x19, [sp, #16 * 9]\n" \ > + " stp x20, x21, [sp, #16 * 10]\n" \ > + " stp x22, x23, [sp, #16 * 11]\n" \ > + " stp x24, x25, [sp, #16 * 12]\n" \ > + " stp x26, x27, [sp, #16 * 13]\n" \ > + " stp x28, x29, [sp, #16 * 14]\n" \ > + " str x30, [sp, #16 * 15]\n" \ > + " mrs x0, nzcv\n" \ > + " str x0, [sp, #8 * 33]\n" > + > + > +#define RESTORE_REGS_STRING\ > + " ldr x0, [sp, #8 * 33]\n" \ > + " msr nzcv, x0\n" \ > + " ldp x0, x1, [sp, #16 * 0]\n" \ > + " ldp x2, x3, [sp, #16 * 1]\n" \ > + " ldp x4, x5, [sp, #16 * 2]\n" \ > + " ldp x6, x7, [sp, #16 * 3]\n" \ > + " ldp x8, x9, [sp, #16 * 4]\n" \ > + " ldp x10, x11, [sp, #16 * 5]\n" \ > + " ldp x12, x13, [sp, #16 * 6]\n" \ > + " ldp x14, x15, [sp, #16 * 7]\n" \ > + " ldp x16, x17, [sp, #16 * 8]\n" \ > + " ldp x18, x19, [sp, #16 * 9]\n" \ > + " ldp x20, x21, [sp, #16 * 10]\n" \ > + " ldp x22, x23, [sp, #16 * 11]\n" \ > + " ldp x24, x25, [sp, #16 * 12]\n" \ > + " ldp x26, x27, [sp, #16 * 13]\n" \ > + " ldp x28, x29, [sp, #16 * 14]\n" \ > + " ldr x30, [sp, #16 * 15]\n" Do we need to restore x19..x28 as they are callee-saved? Okay this all matches up with the definitions of the pt_regs struct. So regs->regs[xn] are all set as is regs->pstate. The hard coded constant offsets make me nervous though, as does the uncertain state of the other elements of the pt_regs struct. > + > #endif /* _ARM_KERNEL_KPROBES_ARM64_H */ > diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c > index 6255814..570218c 100644 > --- a/arch/arm64/kernel/kprobes.c > +++ b/arch/arm64/kernel/kprobes.c > @@ -560,6 +560,32 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) > 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" > + "sub sp, sp, %0\n" > + SAVE_REGS_STRING > + "mov x0, sp\n" > + "bl trampoline_probe_handler\n" > + /* Replace trampoline address in lr with actual > + orig_ret_addr return address. */ > + "str x0, [sp, #16 * 15]\n" > + RESTORE_REGS_STRING > + "add sp, sp, %0\n" > + "ret\n" > + : : "I"(sizeof(struct pt_regs)) : "memory"); I would consider placing something like: BUILD_BUG_ON(offsetof(struct pt_regs, regs) != 0); BUILD_BUG_ON(offsetof(struct pt_regs, pstate) != 264); here to catch changes in pt_regs. Or... Perhaps it makes sense to pull kretprobe_trampoline out into its own .S file? That way you could pull in asm-offsets.h and make use of: S_X0, S_PSTATE and S_FRAME_SIZE. Or something else :-). > +} > + > +static void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs) > +{ > + return (void *) 0; > +} > + > int __init arch_init_kprobes(void) > { > return 0; > -- > 1.8.1.2 > -- 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/