From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751395AbdGQSqb (ORCPT ); Mon, 17 Jul 2017 14:46:31 -0400 Received: from mail-yw0-f195.google.com ([209.85.161.195]:35276 "EHLO mail-yw0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751311AbdGQSq2 (ORCPT ); Mon, 17 Jul 2017 14:46:28 -0400 MIME-Version: 1.0 In-Reply-To: <20170717004603.aeab2a32179d37a8e5dfe857@kernel.org> References: <1500044315-9508-1-git-send-email-francis.deslauriers@efficios.com> <20170716233744.d20dcc9df570c5497852eee2@kernel.org> <20170717004603.aeab2a32179d37a8e5dfe857@kernel.org> From: Francis Deslauriers Date: Mon, 17 Jul 2017 14:46:07 -0400 X-Google-Sender-Auth: mfermOlzjdQfsfRy8-iuGJ5xkGE Message-ID: Subject: Re: [PATCH 0/2] kprobe: Fix: add symbols to kprobe blacklist To: Masami Hiramatsu Cc: rostedt@goodmis.org, peterz@infradead.org, Mathieu Desnoyers , linux-kernel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2017-07-16 11:46 GMT-04:00 Masami Hiramatsu : > > On Sun, 16 Jul 2017 23:37:44 +0900 > Masami Hiramatsu wrote: > > > So, the story what the stack said, > > > > - optimized_callback() calls get_kprobe_ctlblk(), and this_cpu_ptr(&kprobe_ctlblk) caused a page fault (in apic_timer_interrupt, does it cause any problem?) > > - and following call-chain occured > > async_page_fault -> error_entry -> trace_hardirqs_off_thunk -> > > trace_hardirqs_off_caller > > - "mov %gs:0xc400,%rdx" caused async_page_fault() again. > > > > Since trace_hardirqs_off_thunk() stores general registers on > > the stack, there are some noises. > > > > [ 114.429637] FS: 00000000021e7880(0000) GS:ffff88001fd40000(0000) knlGS:0000000000000000 > > > > So, the problem seems that cpu can not access to per-cpu pages. > > OK, I got the root cause of this issue. Since at the irqentry code, > segment registers are not prepared for kernel yet (e.g. interrupted > in user-mode), so we must not optimize it. > I found we had already checked that by checking __entry_text_start/end, > but that is not enough, we need irqentry_text check too. > > Here I made another patch, please try it. Hi, This patch fixes the apic_timer_interrupt crash I was seeing. Thank you! Tested-by: Francis Deslauriers > > ----- > kprobes/x86: Do not jump-optimize kprobes on irq entry code > > From: Masami Hiramatsu > > Since the segment registers are not prepared for kernel > in the irq-entry code, if a kprobe on such code is > jump-optimized, accessing per-cpu variables may cause > kernel panic. > However, if the kprobe is not optimized, it kicks int3 > exception and set segment registers correctly. > > This checks probe-address and if it is in irq-entry code, > it prohibits optimizing such kprobes. This means we can > continuously probing such interrupt handlers by kprobes > but it is not optimized anymore. > > Signed-off-by: Masami Hiramatsu > Reported-by: Francis Deslauriers > --- > arch/x86/entry/entry_64.S | 2 +- > arch/x86/include/asm/unwind.h | 1 + > arch/x86/kernel/kprobes/opt.c | 4 ++-- > arch/x86/kernel/unwind_frame.c | 4 ++-- > 4 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index a9a8027..95bca8b 100644 > --- a/arch/x86/entry/entry_64.S > +++ b/arch/x86/entry/entry_64.S > @@ -675,7 +675,7 @@ apicinterrupt3 \num trace(\sym) smp_trace(\sym) > #endif > > /* Make sure APIC interrupt handlers end up in the irqentry section: */ > -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) > +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || defined(CONFIG_KPROBES) > # define PUSH_SECTION_IRQENTRY .pushsection .irqentry.text, "ax" > # define POP_SECTION_IRQENTRY .popsection > #else > diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h > index e667649..a9896fb9 100644 > --- a/arch/x86/include/asm/unwind.h > +++ b/arch/x86/include/asm/unwind.h > @@ -28,6 +28,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, > bool unwind_next_frame(struct unwind_state *state); > > unsigned long unwind_get_return_address(struct unwind_state *state); > +bool in_entry_code(unsigned long ip); > > static inline bool unwind_done(struct unwind_state *state) > { > diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c > index 69ea0bc..a51c144 100644 > --- a/arch/x86/kernel/kprobes/opt.c > +++ b/arch/x86/kernel/kprobes/opt.c > @@ -39,6 +39,7 @@ > #include > #include > #include > +#include > > #include "common.h" > > @@ -253,8 +254,7 @@ static int can_optimize(unsigned long paddr) > * Do not optimize in the entry code due to the unstable > * stack handling. > */ > - if ((paddr >= (unsigned long)__entry_text_start) && > - (paddr < (unsigned long)__entry_text_end)) > + if (in_entry_code(paddr)) > return 0; > > /* Check there is enough space for a relative jump. */ > diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c > index b9389d7..95123ce 100644 > --- a/arch/x86/kernel/unwind_frame.c > +++ b/arch/x86/kernel/unwind_frame.c > @@ -84,14 +84,14 @@ static size_t regs_size(struct pt_regs *regs) > return sizeof(*regs); > } > > -static bool in_entry_code(unsigned long ip) > +bool in_entry_code(unsigned long ip) > { > char *addr = (char *)ip; > > if (addr >= __entry_text_start && addr < __entry_text_end) > return true; > > -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) > +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || defined(CONFIG_KPROBES) > if (addr >= __irqentry_text_start && addr < __irqentry_text_end) > return true; > #endif > -- > Masami Hiramatsu -- Francis Deslauriers Software developer EfficiOS inc.