From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x242.google.com (mail-pg0-x242.google.com [IPv6:2607:f8b0:400e:c05::242]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3wtS6r4xxFzDvYq for ; Thu, 22 Jun 2017 13:41:24 +1000 (AEST) Received: by mail-pg0-x242.google.com with SMTP id j186so787939pge.1 for ; Wed, 21 Jun 2017 20:41:24 -0700 (PDT) Date: Thu, 22 Jun 2017 13:41:12 +1000 From: Nicholas Piggin To: "Naveen N. Rao" Cc: Michael Ellerman , Ananth N Mavinakayanahalli , Masami Hiramatsu , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v3 4/6] powerpc/64s: Un-blacklist system_call() from kprobes Message-ID: <20170622134112.4bd32543@roar.ozlabs.ibm.com> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 22 Jun 2017 00:08:40 +0530 "Naveen N. Rao" wrote: > It is actually safe to probe system_call() in entry_64.S, but only till > we unset MSR_RI. To allow this, add a new symbol system_call_exit() > after the mtmsrd and blacklist that. Though the mtmsrd instruction > itself is now whitelisted, we won't be allowed to probe on it as we > don't allow probing on rfi and mtmsr instructions (checked for in > arch_prepare_kprobe()). Can you add a little comment to say probes aren't allowed, and it's located after the mtmsr in order to avoid contaminating traces? Also I wonder if a slightly different name would be more instructive? I don't normally care, but the system_call_common code isn't trivial to follow. system_call_exit might give the impression that it is the entire exit path (which would pair with system_call for entry). Perhaps system_call_exit_notrace? No that sucks too :( Thanks, Nick > > Suggested-by: Michael Ellerman > Signed-off-by: Naveen N. Rao > --- > arch/powerpc/kernel/entry_64.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S > index ef8e6615b8ba..feeeadc9aa71 100644 > --- a/arch/powerpc/kernel/entry_64.S > +++ b/arch/powerpc/kernel/entry_64.S > @@ -204,6 +204,7 @@ system_call: /* label this so stack traces look sane */ > mtmsrd r11,1 > #endif /* CONFIG_PPC_BOOK3E */ > > +system_call_exit: > ld r9,TI_FLAGS(r12) > li r11,-MAX_ERRNO > andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK) > @@ -412,7 +413,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) > b . /* prevent speculative execution */ > #endif > _ASM_NOKPROBE_SYMBOL(system_call_common); > -_ASM_NOKPROBE_SYMBOL(system_call); > +_ASM_NOKPROBE_SYMBOL(system_call_exit); > > /* Save non-volatile GPRs, if not already saved. */ > _GLOBAL(save_nvgprs)