Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753344AbcCBVUx (ORCPT ); Wed, 2 Mar 2016 16:20:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55844 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750797AbcCBVUv (ORCPT ); Wed, 2 Mar 2016 16:20:51 -0500 Subject: Re: [PATCH v10 7/9] arm64: Add trampoline code for kretprobes To: Marc Zyngier , David Long , Catalin Marinas , Will Deacon , Sandeepa Prabhu , Pratyush Anand , Steve Capper , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <1456801047-29014-1-git-send-email-dave.long@linaro.org> <1456801047-29014-8-git-send-email-dave.long@linaro.org> <56D5DD27.6040404@arm.com> Cc: Dave P Martin , Mark Rutland , Robin Murphy , Ard Biesheuvel , Jens Wiklander , Christoffer Dall , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Yang Shi , Greg Kroah-Hartman , Viresh Kumar , "Suzuki K. Poulose" , Kees Cook , Zi Shen Lim , John Blackwood , Feng Kan , Balamurugan Shanmugam , James Morse , Vladimir Murzin , Mark Salyzyn , Petr Mladek , Andrew Morton , Mark Brown From: William Cohen Message-ID: <56D7592F.70002@redhat.com> Date: Wed, 2 Mar 2016 16:20:47 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <56D5DD27.6040404@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Wed, 02 Mar 2016 21:20:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7611 Lines: 215 On 03/01/2016 01:19 PM, Marc Zyngier wrote: > On 01/03/16 02:57, 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 original 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 | 2 + >> arch/arm64/kernel/Makefile | 1 + >> arch/arm64/kernel/asm-offsets.c | 22 +++++++++++ >> arch/arm64/kernel/kprobes.c | 5 +++ >> arch/arm64/kernel/kprobes_trampoline.S | 67 ++++++++++++++++++++++++++++++++++ >> 5 files changed, 97 insertions(+) >> create mode 100644 arch/arm64/kernel/kprobes_trampoline.S >> >> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h >> index 79c9511..61b4915 100644 >> --- a/arch/arm64/include/asm/kprobes.h >> +++ b/arch/arm64/include/asm/kprobes.h >> @@ -56,5 +56,7 @@ 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); >> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs); >> >> #endif /* _ARM_KPROBES_H */ >> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile >> index 08325e5..f192b7d 100644 >> --- a/arch/arm64/kernel/Makefile >> +++ b/arch/arm64/kernel/Makefile >> @@ -37,6 +37,7 @@ arm64-obj-$(CONFIG_CPU_IDLE) += cpuidle.o >> arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o >> arm64-obj-$(CONFIG_KGDB) += kgdb.o >> arm64-obj-$(CONFIG_KPROBES) += kprobes.o kprobes-arm64.o \ >> + kprobes_trampoline.o \ >> probes-simulate-insn.o >> arm64-obj-$(CONFIG_EFI) += efi.o efi-entry.stub.o >> arm64-obj-$(CONFIG_PCI) += pci.o >> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c >> index fffa4ac6..460b54c 100644 >> --- a/arch/arm64/kernel/asm-offsets.c >> +++ b/arch/arm64/kernel/asm-offsets.c >> @@ -50,6 +50,28 @@ int main(void) >> DEFINE(S_X5, offsetof(struct pt_regs, regs[5])); >> DEFINE(S_X6, offsetof(struct pt_regs, regs[6])); >> DEFINE(S_X7, offsetof(struct pt_regs, regs[7])); >> + DEFINE(S_X8, offsetof(struct pt_regs, regs[8])); >> + DEFINE(S_X9, offsetof(struct pt_regs, regs[9])); >> + DEFINE(S_X10, offsetof(struct pt_regs, regs[10])); >> + DEFINE(S_X11, offsetof(struct pt_regs, regs[11])); >> + DEFINE(S_X12, offsetof(struct pt_regs, regs[12])); >> + DEFINE(S_X13, offsetof(struct pt_regs, regs[13])); >> + DEFINE(S_X14, offsetof(struct pt_regs, regs[14])); >> + DEFINE(S_X15, offsetof(struct pt_regs, regs[15])); >> + DEFINE(S_X16, offsetof(struct pt_regs, regs[16])); >> + DEFINE(S_X17, offsetof(struct pt_regs, regs[17])); >> + DEFINE(S_X18, offsetof(struct pt_regs, regs[18])); >> + DEFINE(S_X19, offsetof(struct pt_regs, regs[19])); >> + DEFINE(S_X20, offsetof(struct pt_regs, regs[20])); >> + DEFINE(S_X21, offsetof(struct pt_regs, regs[21])); >> + DEFINE(S_X22, offsetof(struct pt_regs, regs[22])); >> + DEFINE(S_X23, offsetof(struct pt_regs, regs[23])); >> + DEFINE(S_X24, offsetof(struct pt_regs, regs[24])); >> + DEFINE(S_X25, offsetof(struct pt_regs, regs[25])); >> + DEFINE(S_X26, offsetof(struct pt_regs, regs[26])); >> + DEFINE(S_X27, offsetof(struct pt_regs, regs[27])); >> + DEFINE(S_X28, offsetof(struct pt_regs, regs[28])); >> + DEFINE(S_X29, offsetof(struct pt_regs, regs[29])); > > Do we need all of these? Specially considering that we're only using the > even ones? You may want to consider something like > arch/arm64/kvm/hyp/entry.S does. Following what arch/arm64/kvm/hyp/entry.S does would make the patch a bit smaller. > >> DEFINE(S_LR, offsetof(struct pt_regs, regs[30])); >> DEFINE(S_SP, offsetof(struct pt_regs, sp)); >> #ifdef CONFIG_COMPAT >> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c >> index ffc5affd..98f4fe5 100644 >> --- a/arch/arm64/kernel/kprobes.c >> +++ b/arch/arm64/kernel/kprobes.c >> @@ -532,6 +532,11 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) >> return 1; >> } >> >> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs) >> +{ >> + return (void *) 0; > > Something wrong with NULL? ;-) Nothing wrong with using NULL. > >> +} >> + >> int __init arch_init_kprobes(void) >> { >> return 0; >> diff --git a/arch/arm64/kernel/kprobes_trampoline.S b/arch/arm64/kernel/kprobes_trampoline.S >> new file mode 100644 >> index 0000000..5a336cf >> --- /dev/null >> +++ b/arch/arm64/kernel/kprobes_trampoline.S >> @@ -0,0 +1,67 @@ >> +/* >> + * trampoline entry and return code for kretprobes. >> + */ >> + >> +#include >> +#include > > #include > >> + >> + .text >> + >> +ENTRY(kretprobe_trampoline) >> + >> + sub sp, sp, #S_FRAME_SIZE >> + >> + stp x0, x1, [sp, #S_X0] >> + stp x2, x3, [sp, #S_X2] >> + stp x4, x5, [sp, #S_X4] >> + stp x6, x7, [sp, #S_X6] >> + stp x8, x9, [sp, #S_X8] >> + stp x10, x11, [sp, #S_X10] >> + stp x12, x13, [sp, #S_X12] >> + stp x14, x15, [sp, #S_X14] >> + stp x16, x17, [sp, #S_X16] >> + stp x18, x19, [sp, #S_X18] >> + stp x20, x21, [sp, #S_X20] >> + stp x22, x23, [sp, #S_X22] >> + stp x24, x25, [sp, #S_X24] >> + stp x26, x27, [sp, #S_X26] >> + stp x28, x29, [sp, #S_X28] >> + str x30, [sp, #S_LR] > > Might as well call it LR? Given the code is going to overwrite lr with the value returned by trampoline_probe_handler might eliminate the store to #S_LR above. > >> + add x0, sp, #S_FRAME_SIZE >> + str x0, [sp, #S_SP] >> + mrs x0, nzcv >> + mrs x1, daif >> + orr x0, x0, x1 >> + /* There seems no easy way to get the mode field so make one up */ >> + add x0, x0, #5 > > Do you mean something like CurrentEL? You could also save SPSel whilst > you're at it. Looking at the my patch again I am wondering if the patch could skip storing daif and the mode field. The nzcv bit are the only thing restored. > >> + str x0, [sp, #S_PSTATE] >> + >> + mov x0, sp >> + bl trampoline_probe_handler >> + /* Replace trampoline address in lr with actual >> + orig_ret_addr return address. */ >> + str x0, [sp, #S_LR] > > Why do you need to store it on the stack? You could do a "mov lr, x0", > and drop the last load of the sequence below... Ah, yes, that would save a store/load pair. >> + >> + ldr x0, [sp, #S_PSTATE] >> + msr nzcv, x0 >> + ldp x0, x1, [sp, #S_X0] >> + ldp x2, x3, [sp, #S_X2] >> + ldp x4, x5, [sp, #S_X4] >> + ldp x6, x7, [sp, #S_X6] >> + ldp x8, x9, [sp, #S_X8] >> + ldp x10, x11, [sp, #S_X10] >> + ldp x12, x13, [sp, #S_X12] >> + ldp x14, x15, [sp, #S_X14] >> + ldp x16, x17, [sp, #S_X16] >> + ldp x18, x19, [sp, #S_X18] >> + ldp x20, x21, [sp, #S_X20] >> + ldp x22, x23, [sp, #S_X22] >> + ldp x24, x25, [sp, #S_X24] >> + ldp x26, x27, [sp, #S_X26] >> + ldp x28, x29, [sp, #S_X28] >> + ldr x30, [sp, #S_LR] >> + >> + add sp, sp, #S_FRAME_SIZE >> + ret >> + >> +ENDPROC(kretprobe_trampoline) >> > > Thanks, > > M. > Thanks, -Will