From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3904782-1526647136-2-3970912734093438101 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.248, MAILING_LIST_MULTI -1, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='US', FromHeader='au', MailFrom='org' X-Spam-charsets: X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: linux-api-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=fm2; t= 1526647135; b=m5Nv7NH9/rnU/pkc/pnqduq3meSJvUysFQww7k8FaO89aeelus FEBs9IN0KvogwTuSP5Wcp+zYQ+kGjzcVZdB14RwFow5H0m+tKV8hAPYIvWmzBSuy ZxJdiO7Iaoejywk9MwErWkBRp0GxST9AgDhpRO3RpJcFdVs6/6iVCJPCjNfjWR5t Dv+voWvi0cN8SLKGn/o0Vf8nz2GSE99zRrF+0wyuuaecnsTM8PF6vIT+3uxVBaIc ffmp5TLSsfdo857QYjkE+B4M76IRrGijkBD8s567DPl+Fap/7avw9qUM+x6PXjR1 QWrf4EchbdVfwDLLld5qL/ZvyjM2z8BXE9Cw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=from:to:cc:subject:in-reply-to:references :date:message-id:mime-version:content-type:sender:list-id; s= fm2; t=1526647135; bh=fdSm/ohAct085C7uHMESnnOUChN/r1UzYXMAWgmb7W c=; b=eLGUmHWD6+Z7G9JJ8L8UW90YDqrp9vjjXaRbfdrSJGY6k5OHigL07NVSpp xpnIQUEq8gHXcp3AYJOeyeo5xmO44ZmKijVGYNr49Wpv5UieKx5WyaMSTofT/ZJm aqovrBJO/W0XnbTpJRFxpyNw+8VEF+EpolTx59lqAwmx7tIZq5eGiZoLRwPvTMMs PhC71bwhEVrMbwACdbVjdJdWR4a9Jod+h5vgI1KQSnN83qT9+lMtUi8FKe3h29D5 Vwzfh3RV43ZH7ay94IZCwaGhgnGNGRInlpN+mGpBaxr4qQL5qD4SvZLUka7vQw+C SBrFUkdLZVuoawDX4/9rOKSvCa5w== ARC-Authentication-Results: i=1; mx3.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=ellerman.id.au; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=ellerman.id.au header.result=pass header_is_org_domain=yes; x-vs=clean score=-100 state=0 Authentication-Results: mx3.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=ellerman.id.au; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=linux-api-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=ellerman.id.au header.result=pass header_is_org_domain=yes; x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfJsYzc32RqbdC7N8ar+/QKryz5+0onHOlndPcz31ama1+5Vntloj7/S3B8c1qZaS/sAI2K2Ytb8MCz+iwCWrHeD8ZCyKfxMIaN+Jsi2hkuEpWamC4Y/9 VYOB0ieB307sqBfrt50eNkbDRpMv68fIU2wZ91K4Lp5+Xz0CKat1xIOu0DS4YR7/5pPhjltiiUMmbIyiRfcnO6QKYle8slzo0cucWA2NCjSQl8F2HHLz5XHc X-CM-Analysis: v=2.3 cv=Tq3Iegfh c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=VUJBJC2UJ8kA:10 a=7d_E57ReAAAA:8 a=pGLkceISAAAA:8 a=JfrnYn6hAAAA:8 a=VwQbUJbxAAAA:8 a=w3vVgvQxHcbt_4zMOR4A:9 a=rLlfUyBxKXTqtY8U:21 a=7t7ie_civxxDy9oR:21 a=9uJS9M6w_WAA:10 a=x8gzFH9gYPwA:10 a=jhqOcbufqs7Y1TYCrUUU:22 a=1CNFftbPRP8L7MoqJWF3:22 a=AjGcO6oz07-iQ99wixmX:22 a=M4RU-Flaiq8Hmqv6YSws:22 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751296AbeERMix (ORCPT ); Fri, 18 May 2018 08:38:53 -0400 Received: from ozlabs.org ([203.11.71.1]:41267 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750841AbeERMiw (ORCPT ); Fri, 18 May 2018 08:38:52 -0400 Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au From: Michael Ellerman To: Mathieu Desnoyers , Boqun Feng , Will Deacon Cc: Peter Zijlstra , "Paul E. McKenney" , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Michael Kerrisk , Joel Fernandes , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences In-Reply-To: <277374719.2144.1526570889798.JavaMail.zimbra@efficios.com> References: <20180430224433.17407-1-mathieu.desnoyers@efficios.com> <20180430224433.17407-8-mathieu.desnoyers@efficios.com> <20180516161837.GI12198@hirez.programming.kicks-ass.net> <112970629.1913.1526501596485.JavaMail.zimbra@efficios.com> <20180517011949.GA1121@tardis> <277374719.2144.1526570889798.JavaMail.zimbra@efficios.com> Date: Fri, 18 May 2018 22:38:44 +1000 Message-ID: <87sh6pxhnv.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Mathieu Desnoyers writes: > ----- On May 16, 2018, at 9:19 PM, Boqun Feng boqun.feng@gmail.com wrote: >> On Wed, May 16, 2018 at 04:13:16PM -0400, Mathieu Desnoyers wrote: >>> ----- On May 16, 2018, at 12:18 PM, Peter Zijlstra peterz@infradead.org wrote: >>> > On Mon, Apr 30, 2018 at 06:44:26PM -0400, Mathieu Desnoyers wrote: >>> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >>> >> index c32a181a7cbb..ed21a777e8c6 100644 >>> >> --- a/arch/powerpc/Kconfig >>> >> +++ b/arch/powerpc/Kconfig >>> >> @@ -223,6 +223,7 @@ config PPC >>> >> select HAVE_SYSCALL_TRACEPOINTS >>> >> select HAVE_VIRT_CPU_ACCOUNTING >>> >> select HAVE_IRQ_TIME_ACCOUNTING >>> >> + select HAVE_RSEQ >>> >> select IRQ_DOMAIN >>> >> select IRQ_FORCED_THREADING >>> >> select MODULES_USE_ELF_RELA >>> >> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c >>> >> index 61db86ecd318..d3bb3aaaf5ac 100644 >>> >> --- a/arch/powerpc/kernel/signal.c >>> >> +++ b/arch/powerpc/kernel/signal.c >>> >> @@ -133,6 +133,8 @@ static void do_signal(struct task_struct *tsk) >>> >> /* Re-enable the breakpoints for the signal stack */ >>> >> thread_change_pc(tsk, tsk->thread.regs); >>> >> >>> >> + rseq_signal_deliver(tsk->thread.regs); >>> >> + >>> >> if (is32) { >>> >> if (ksig.ka.sa.sa_flags & SA_SIGINFO) >>> >> ret = handle_rt_signal32(&ksig, oldset, tsk); >>> >> @@ -164,6 +166,7 @@ void do_notify_resume(struct pt_regs *regs, unsigned long >>> >> thread_info_flags) >>> >> if (thread_info_flags & _TIF_NOTIFY_RESUME) { >>> >> clear_thread_flag(TIF_NOTIFY_RESUME); >>> >> tracehook_notify_resume(regs); >>> >> + rseq_handle_notify_resume(regs); >>> >> } >>> >> >>> >> user_enter(); >>> > >>> > Again no rseq_syscall(). >>> >>> Same question for PowerPC as for ARM: >>> >>> Considering that rseq_syscall is implemented as follows: >>> >>> +void rseq_syscall(struct pt_regs *regs) >>> +{ >>> + unsigned long ip = instruction_pointer(regs); >>> + struct task_struct *t = current; >>> + struct rseq_cs rseq_cs; >>> + >>> + if (!t->rseq) >>> + return; >>> + if (!access_ok(VERIFY_READ, t->rseq, sizeof(*t->rseq)) || >>> + rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs)) >>> + force_sig(SIGSEGV, t); >>> +} >>> >>> and that x86 calls it from syscall_return_slowpath() (which AFAIU is >>> now used in the fast-path since KPTI), I wonder where we should call >> >> So we actually detect this after the syscall takes effect, right? I >> wonder whether this could be problematic, because "disallowing syscall" >> in rseq areas may means the syscall won't take effect to some people, I >> guess? >> >>> this on PowerPC ? I was under the impression that PowerPC return to >>> userspace fast-path was not calling C code unless work flags were set, >>> but I might be wrong. >>> >> >> I think you're right. So we have to introduce callsite to rseq_syscall() >> in syscall path, something like: >> >> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S >> index 51695608c68b..a25734a96640 100644 >> --- a/arch/powerpc/kernel/entry_64.S >> +++ b/arch/powerpc/kernel/entry_64.S >> @@ -222,6 +222,9 @@ system_call_exit: >> mtmsrd r11,1 >> #endif /* CONFIG_PPC_BOOK3E */ >> >> + addi r3,r1,STACK_FRAME_OVERHEAD >> + bl rseq_syscall >> + >> ld r9,TI_FLAGS(r12) >> li r11,-MAX_ERRNO >> andi. >> r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK) >> >> But I think it's important for us to first decide where (before or after >> the syscall) we do the detection. > > As Peter said, we don't really care whether it's on syscall entry or exit, as > long as the process gets killed when the erroneous use is detected. I think doing > it on syscall exit is a bit easier because we can clearly access the userspace > TLS, which AFAIU may be less straightforward on syscall entry. Coming in to the thread late, sorry if I'm missing the point. > We may want to add #ifdef CONFIG_DEBUG_RSEQ / #endif around the code you > proposed above, so it's only compiled in if CONFIG_DEBUG_RSEQ=y. That sounds good. A function call is not free even if it returns immediately. > On the ARM leg of the email thread, Will Deacon suggests to test whether current->rseq > is non-NULL before calling rseq_syscall(). I wonder if this added check is justified > as the assembly level, considering that this is just a debugging option. We already do > that check at the very beginning of rseq_syscall(). I guess it depends if this is one of those "debugging options" that's going to end up turned on in distro kernels? I think in that code we'd need to check paca->current->rseq, so that wouldn't be free either. cheers From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Ellerman Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences Date: Fri, 18 May 2018 22:38:44 +1000 Message-ID: <87sh6pxhnv.fsf@concordia.ellerman.id.au> References: <20180430224433.17407-1-mathieu.desnoyers@efficios.com> <20180430224433.17407-8-mathieu.desnoyers@efficios.com> <20180516161837.GI12198@hirez.programming.kicks-ass.net> <112970629.1913.1526501596485.JavaMail.zimbra@efficios.com> <20180517011949.GA1121@tardis> <277374719.2144.1526570889798.JavaMail.zimbra@efficios.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <277374719.2144.1526570889798.JavaMail.zimbra@efficios.com> Sender: linux-kernel-owner@vger.kernel.org To: Mathieu Desnoyers , Boqun Feng , Will Deacon Cc: Peter Zijlstra , "Paul E. McKenney" , Andy Lutomirski , Dave Watson , linux-kernel , linux-api , Paul Turner , Andrew Morton , Russell King , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Hunter , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Michael List-Id: linux-api@vger.kernel.org Mathieu Desnoyers writes: > ----- On May 16, 2018, at 9:19 PM, Boqun Feng boqun.feng@gmail.com wrote: >> On Wed, May 16, 2018 at 04:13:16PM -0400, Mathieu Desnoyers wrote: >>> ----- On May 16, 2018, at 12:18 PM, Peter Zijlstra peterz@infradead.org wrote: >>> > On Mon, Apr 30, 2018 at 06:44:26PM -0400, Mathieu Desnoyers wrote: >>> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >>> >> index c32a181a7cbb..ed21a777e8c6 100644 >>> >> --- a/arch/powerpc/Kconfig >>> >> +++ b/arch/powerpc/Kconfig >>> >> @@ -223,6 +223,7 @@ config PPC >>> >> select HAVE_SYSCALL_TRACEPOINTS >>> >> select HAVE_VIRT_CPU_ACCOUNTING >>> >> select HAVE_IRQ_TIME_ACCOUNTING >>> >> + select HAVE_RSEQ >>> >> select IRQ_DOMAIN >>> >> select IRQ_FORCED_THREADING >>> >> select MODULES_USE_ELF_RELA >>> >> diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c >>> >> index 61db86ecd318..d3bb3aaaf5ac 100644 >>> >> --- a/arch/powerpc/kernel/signal.c >>> >> +++ b/arch/powerpc/kernel/signal.c >>> >> @@ -133,6 +133,8 @@ static void do_signal(struct task_struct *tsk) >>> >> /* Re-enable the breakpoints for the signal stack */ >>> >> thread_change_pc(tsk, tsk->thread.regs); >>> >> >>> >> + rseq_signal_deliver(tsk->thread.regs); >>> >> + >>> >> if (is32) { >>> >> if (ksig.ka.sa.sa_flags & SA_SIGINFO) >>> >> ret = handle_rt_signal32(&ksig, oldset, tsk); >>> >> @@ -164,6 +166,7 @@ void do_notify_resume(struct pt_regs *regs, unsigned long >>> >> thread_info_flags) >>> >> if (thread_info_flags & _TIF_NOTIFY_RESUME) { >>> >> clear_thread_flag(TIF_NOTIFY_RESUME); >>> >> tracehook_notify_resume(regs); >>> >> + rseq_handle_notify_resume(regs); >>> >> } >>> >> >>> >> user_enter(); >>> > >>> > Again no rseq_syscall(). >>> >>> Same question for PowerPC as for ARM: >>> >>> Considering that rseq_syscall is implemented as follows: >>> >>> +void rseq_syscall(struct pt_regs *regs) >>> +{ >>> + unsigned long ip = instruction_pointer(regs); >>> + struct task_struct *t = current; >>> + struct rseq_cs rseq_cs; >>> + >>> + if (!t->rseq) >>> + return; >>> + if (!access_ok(VERIFY_READ, t->rseq, sizeof(*t->rseq)) || >>> + rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs)) >>> + force_sig(SIGSEGV, t); >>> +} >>> >>> and that x86 calls it from syscall_return_slowpath() (which AFAIU is >>> now used in the fast-path since KPTI), I wonder where we should call >> >> So we actually detect this after the syscall takes effect, right? I >> wonder whether this could be problematic, because "disallowing syscall" >> in rseq areas may means the syscall won't take effect to some people, I >> guess? >> >>> this on PowerPC ? I was under the impression that PowerPC return to >>> userspace fast-path was not calling C code unless work flags were set, >>> but I might be wrong. >>> >> >> I think you're right. So we have to introduce callsite to rseq_syscall() >> in syscall path, something like: >> >> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S >> index 51695608c68b..a25734a96640 100644 >> --- a/arch/powerpc/kernel/entry_64.S >> +++ b/arch/powerpc/kernel/entry_64.S >> @@ -222,6 +222,9 @@ system_call_exit: >> mtmsrd r11,1 >> #endif /* CONFIG_PPC_BOOK3E */ >> >> + addi r3,r1,STACK_FRAME_OVERHEAD >> + bl rseq_syscall >> + >> ld r9,TI_FLAGS(r12) >> li r11,-MAX_ERRNO >> andi. >> r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK) >> >> But I think it's important for us to first decide where (before or after >> the syscall) we do the detection. > > As Peter said, we don't really care whether it's on syscall entry or exit, as > long as the process gets killed when the erroneous use is detected. I think doing > it on syscall exit is a bit easier because we can clearly access the userspace > TLS, which AFAIU may be less straightforward on syscall entry. Coming in to the thread late, sorry if I'm missing the point. > We may want to add #ifdef CONFIG_DEBUG_RSEQ / #endif around the code you > proposed above, so it's only compiled in if CONFIG_DEBUG_RSEQ=y. That sounds good. A function call is not free even if it returns immediately. > On the ARM leg of the email thread, Will Deacon suggests to test whether current->rseq > is non-NULL before calling rseq_syscall(). I wonder if this added check is justified > as the assembly level, considering that this is just a debugging option. We already do > that check at the very beginning of rseq_syscall(). I guess it depends if this is one of those "debugging options" that's going to end up turned on in distro kernels? I think in that code we'd need to check paca->current->rseq, so that wouldn't be free either. cheers