From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8B30C77B6E for ; Wed, 12 Apr 2023 09:02:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229888AbjDLJCY (ORCPT ); Wed, 12 Apr 2023 05:02:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229506AbjDLJCU (ORCPT ); Wed, 12 Apr 2023 05:02:20 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 28452A9 for ; Wed, 12 Apr 2023 02:02:19 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 53BB5C14; Wed, 12 Apr 2023 02:03:03 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.21.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E7B153F587; Wed, 12 Apr 2023 02:02:17 -0700 (PDT) Date: Wed, 12 Apr 2023 10:02:15 +0100 From: Mark Rutland To: Heiko Carstens Cc: Kees Cook , Alexander Popov , Vasily Gorbik , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] s390/stackleak: provide fast __stackleak_poison() implementation Message-ID: References: <20230405130841.1350565-1-hca@linux.ibm.com> <20230405130841.1350565-3-hca@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230405130841.1350565-3-hca@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 05, 2023 at 03:08:41PM +0200, Heiko Carstens wrote: > Provide an s390 specific __stackleak_poison() implementation which is > faster than the generic variant. > > For the original implementation with an enforced 4kb stackframe for the > getpid() system call the system call overhead increases by a factor of 3 if > the stackleak feature is enabled. Using the s390 mvc based variant this is > reduced to an increase of 25% instead. > > This is within the expected area, since the mvc based implementation is > more or less a memset64() variant which comes with similar results. See > commit 0b77d6701cf8 ("s390: implement memset16, memset32 & memset64"). With that in mind, could we use memset64() directly (if we made it noninstr-safe)? Mark. > > Reviewed-by: Vasily Gorbik > Signed-off-by: Heiko Carstens > --- > arch/s390/include/asm/processor.h | 35 +++++++++++++++++++++++++++++++ > 1 file changed, 35 insertions(+) > > diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h > index efffc28cbad8..dc17896a001a 100644 > --- a/arch/s390/include/asm/processor.h > +++ b/arch/s390/include/asm/processor.h > @@ -118,6 +118,41 @@ unsigned long vdso_size(void); > > #define HAVE_ARCH_PICK_MMAP_LAYOUT > > +#define __stackleak_poison __stackleak_poison > +static __always_inline void __stackleak_poison(unsigned long erase_low, > + unsigned long erase_high, > + unsigned long poison) > +{ > + unsigned long tmp, count; > + > + count = erase_high - erase_low; > + if (!count) > + return; > + asm volatile( > + " cghi %[count],8\n" > + " je 2f\n" > + " aghi %[count],-(8+1)\n" > + " srlg %[tmp],%[count],8\n" > + " ltgr %[tmp],%[tmp]\n" > + " jz 1f\n" > + "0: stg %[poison],0(%[addr])\n" > + " mvc 8(256-8,%[addr]),0(%[addr])\n" > + " la %[addr],256(%[addr])\n" > + " brctg %[tmp],0b\n" > + "1: stg %[poison],0(%[addr])\n" > + " larl %[tmp],3f\n" > + " ex %[count],0(%[tmp])\n" > + " j 4f\n" > + "2: stg %[poison],0(%[addr])\n" > + " j 4f\n" > + "3: mvc 8(1,%[addr]),0(%[addr])\n" > + "4:\n" > + : [addr] "+&a" (erase_low), [count] "+&d" (count), [tmp] "=&a" (tmp) > + : [poison] "d" (poison) > + : "memory", "cc" > + ); > +} > + > /* > * Thread structure > */ > -- > 2.37.2 >