From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Naveen N. Rao" Subject: Re: [RFC PATCH -tip v5 24/27] bpf: error-inject: kprobes: Clear current_kprobe and enable preempt in kprobe Date: Thu, 07 Jun 2018 17:12:18 +0530 Message-ID: <1528371714.iz71qgzxv3.naveen@linux.ibm.com> References: <152812730943.10068.5166429445118734697.stgit@devbox> <152812800822.10068.3306094708706993432.stgit@devbox> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: <152812800822.10068.3306094708706993432.stgit@devbox> Sender: linux-kernel-owner@vger.kernel.org To: Masami Hiramatsu , Ingo Molnar , Thomas Gleixner Cc: Andrew Morton , Alexei Starovoitov , Catalin Marinas , Rich Felker , "David S. Miller" , Fenghua Yu , Heiko Carstens , "H . Peter Anvin" , Josef Bacik , James Hogan , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Russell King , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-snps-arc@lists.infradead.org, Ingo Molnar , Paul Mackerras , Ralf Baechle List-Id: linux-arch.vger.kernel.org Masami Hiramatsu wrote: > Clear current_kprobe and enable preemption in kprobe > even if pre_handler returns !0. > > This simplifies function override using kprobes. > > Jprobe used to require to keep the preemption disabled and > keep current_kprobe until it returned to original function > entry. For this reason kprobe_int3_handler() and similar > arch dependent kprobe handers checks pre_handler result > and exit without enabling preemption if the result is !0. > > After removing the jprobe, Kprobes does not need to > keep preempt disabled even if user handler returns !0 > anymore. > > But since the function override handler in error-inject > and bpf is also returns !0 if it overrides a function, > to balancing the preempt count, it enables preemption > and reset current kprobe by itself. > > That is a bad design that is very buggy. This fixes > such unbalanced preempt-count and current_kprobes setting > in kprobes, bpf and error-inject. > > Note: for powerpc and x86, this removes all preempt_disable > from kprobe_ftrace_handler because ftrace callbacks are > called under preempt disabled. > > Signed-off-by: Masami Hiramatsu > Cc: Vineet Gupta > Cc: Russell King > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Tony Luck > Cc: Fenghua Yu > Cc: Ralf Baechle > Cc: James Hogan > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > Cc: Martin Schwidefsky > Cc: Heiko Carstens > Cc: Yoshinori Sato > Cc: Rich Felker > Cc: "David S. Miller" > Cc: "Naveen N. Rao" > Cc: Josef Bacik > Cc: Alexei Starovoitov > Cc: x86@kernel.org > Cc: linux-snps-arc@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-ia64@vger.kernel.org > Cc: linux-mips@linux-mips.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: linux-s390@vger.kernel.org > Cc: linux-sh@vger.kernel.org > Cc: sparclinux@vger.kernel.org > --- > Changes in v5: > - Fix kprobe_ftrace_handler in arch/powerpc too. > --- > arch/arc/kernel/kprobes.c | 5 +++-- > arch/arm/probes/kprobes/core.c | 10 +++++----- > arch/arm64/kernel/probes/kprobes.c | 10 +++++----- > arch/ia64/kernel/kprobes.c | 13 ++++--------- > arch/mips/kernel/kprobes.c | 4 ++-- > arch/powerpc/kernel/kprobes-ftrace.c | 15 ++++++--------- > arch/powerpc/kernel/kprobes.c | 7 +++++-- For the powerpc bits: Acked-by: Naveen N. Rao Thanks, Naveen From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:55768 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932357AbeFGLmd (ORCPT ); Thu, 7 Jun 2018 07:42:33 -0400 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w57Bd5xd074138 for ; Thu, 7 Jun 2018 07:42:33 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 2jf3ucrjg0-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 07 Jun 2018 07:42:33 -0400 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 7 Jun 2018 12:42:30 +0100 Date: Thu, 07 Jun 2018 17:12:18 +0530 From: "Naveen N. Rao" Subject: Re: [RFC PATCH -tip v5 24/27] bpf: error-inject: kprobes: Clear current_kprobe and enable preempt in kprobe References: <152812730943.10068.5166429445118734697.stgit@devbox> <152812800822.10068.3306094708706993432.stgit@devbox> In-Reply-To: <152812800822.10068.3306094708706993432.stgit@devbox> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8BIT Message-ID: <1528371714.iz71qgzxv3.naveen@linux.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Masami Hiramatsu , Ingo Molnar , Thomas Gleixner Cc: Andrew Morton , Alexei Starovoitov , Catalin Marinas , Rich Felker , "David S. Miller" , Fenghua Yu , Heiko Carstens , "H . Peter Anvin" , Josef Bacik , James Hogan , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Russell King , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-snps-arc@lists.infradead.org, Ingo Molnar , Paul Mackerras , Ralf Baechle , Steven Rostedt , Martin Schwidefsky , sparclinux@vger.kernel.org, Tony Luck , Vineet Gupta , Will Deacon , x86@kernel.org, Yoshinori Sato Message-ID: <20180607114218.vz7jq62qaplgKeBaBW-1YE9EQ6QA75zuiRRzct03p4c@z> Masami Hiramatsu wrote: > Clear current_kprobe and enable preemption in kprobe > even if pre_handler returns !0. > > This simplifies function override using kprobes. > > Jprobe used to require to keep the preemption disabled and > keep current_kprobe until it returned to original function > entry. For this reason kprobe_int3_handler() and similar > arch dependent kprobe handers checks pre_handler result > and exit without enabling preemption if the result is !0. > > After removing the jprobe, Kprobes does not need to > keep preempt disabled even if user handler returns !0 > anymore. > > But since the function override handler in error-inject > and bpf is also returns !0 if it overrides a function, > to balancing the preempt count, it enables preemption > and reset current kprobe by itself. > > That is a bad design that is very buggy. This fixes > such unbalanced preempt-count and current_kprobes setting > in kprobes, bpf and error-inject. > > Note: for powerpc and x86, this removes all preempt_disable > from kprobe_ftrace_handler because ftrace callbacks are > called under preempt disabled. > > Signed-off-by: Masami Hiramatsu > Cc: Vineet Gupta > Cc: Russell King > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Tony Luck > Cc: Fenghua Yu > Cc: Ralf Baechle > Cc: James Hogan > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > Cc: Martin Schwidefsky > Cc: Heiko Carstens > Cc: Yoshinori Sato > Cc: Rich Felker > Cc: "David S. Miller" > Cc: "Naveen N. Rao" > Cc: Josef Bacik > Cc: Alexei Starovoitov > Cc: x86@kernel.org > Cc: linux-snps-arc@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-ia64@vger.kernel.org > Cc: linux-mips@linux-mips.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: linux-s390@vger.kernel.org > Cc: linux-sh@vger.kernel.org > Cc: sparclinux@vger.kernel.org > --- > Changes in v5: > - Fix kprobe_ftrace_handler in arch/powerpc too. > --- > arch/arc/kernel/kprobes.c | 5 +++-- > arch/arm/probes/kprobes/core.c | 10 +++++----- > arch/arm64/kernel/probes/kprobes.c | 10 +++++----- > arch/ia64/kernel/kprobes.c | 13 ++++--------- > arch/mips/kernel/kprobes.c | 4 ++-- > arch/powerpc/kernel/kprobes-ftrace.c | 15 ++++++--------- > arch/powerpc/kernel/kprobes.c | 7 +++++-- For the powerpc bits: Acked-by: Naveen N. Rao Thanks, Naveen