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[209.132.180.67]) by mx.google.com with ESMTP id w19-v6si8687727plp.304.2018.10.05.10.05.02; Fri, 05 Oct 2018 10:05:17 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729246AbeJFACp (ORCPT + 99 others); Fri, 5 Oct 2018 20:02:45 -0400 Received: from mga03.intel.com ([134.134.136.65]:61174 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728214AbeJFACp (ORCPT ); Fri, 5 Oct 2018 20:02:45 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Oct 2018 10:03:08 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,345,1534834800"; d="scan'208";a="78790390" Received: from 2b52.sc.intel.com ([143.183.136.147]) by orsmga007.jf.intel.com with ESMTP; 05 Oct 2018 10:03:07 -0700 Message-ID: Subject: Re: [RFC PATCH v4 3/9] x86/cet/ibt: Add IBT legacy code bitmap allocation function From: Yu-cheng Yu To: Andy Lutomirski Cc: Eugene Syromiatnikov , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue Date: Fri, 05 Oct 2018 09:58:24 -0700 In-Reply-To: <5BF3AE8F-CC2A-4160-9FF6-FEA171A76371@amacapital.net> References: <20180921150553.21016-1-yu-cheng.yu@intel.com> <20180921150553.21016-4-yu-cheng.yu@intel.com> <20181003195702.GF32759@asgard.redhat.com> <5BF3AE8F-CC2A-4160-9FF6-FEA171A76371@amacapital.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2018-10-05 at 09:28 -0700, Andy Lutomirski wrote: > > On Oct 5, 2018, at 9:13 AM, Yu-cheng Yu wrote: > > > > > On Wed, 2018-10-03 at 21:57 +0200, Eugene Syromiatnikov wrote: > > > > On Fri, Sep 21, 2018 at 08:05:47AM -0700, Yu-cheng Yu wrote: > > > > Indirect branch tracking provides an optional legacy code bitmap > > > > that indicates locations of non-IBT compatible code. When set, > > > > each bit in the bitmap represents a page in the linear address is > > > > legacy code. > > > > > > > > We allocate the bitmap only when the application requests it. > > > > Most applications do not need the bitmap. > > > > > > > > Signed-off-by: Yu-cheng Yu > > > > --- > > > > arch/x86/kernel/cet.c | 45 +++++++++++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 45 insertions(+) > > > > > > > > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > > > > index 6adfe795d692..a65d9745af08 100644 > > > > --- a/arch/x86/kernel/cet.c > > > > +++ b/arch/x86/kernel/cet.c > > > > @@ -314,3 +314,48 @@ void cet_disable_ibt(void) > > > > wrmsrl(MSR_IA32_U_CET, r); > > > > current->thread.cet.ibt_enabled = 0; > > > > } > > > > + > > > > +int cet_setup_ibt_bitmap(void) > > > > +{ > > > > + u64 r; > > > > + unsigned long bitmap; > > > > + unsigned long size; > > > > + > > > > + if (!cpu_feature_enabled(X86_FEATURE_IBT)) > > > > + return -EOPNOTSUPP; > > > > + > > > > + if (!current->thread.cet.ibt_bitmap_addr) { > > > > + /* > > > > + * Calculate size and put in thread header. > > > > + * may_expand_vm() needs this information. > > > > + */ > > > > + size = TASK_SIZE / PAGE_SIZE / BITS_PER_BYTE; > > > > > > TASK_SIZE_MAX is likely needed here, as an application can easily switch > > > between long an 32-bit protected mode. And then the case of a CPU that > > > doesn't support 5LPT. > > > > If we had calculated bitmap size from TASK_SIZE_MAX, all 32-bit apps would > > have > > failed the allocation for bitmap size > TASK_SIZE. Please see values below, > > which is printed from the current code. > > > > Yu-cheng > > > > > > x64: > > TASK_SIZE_MAX = 0000 7fff ffff f000 > > TASK_SIZE = 0000 7fff ffff f000 > > bitmap size = 0000 0000 ffff ffff > > > > x32: > > TASK_SIZE_MAX = 0000 7fff ffff f000 > > TASK_SIZE = 0000 0000 ffff e000 > > bitmap size = 0000 0000 0001 ffff > > > > I haven’t followed all the details here, but I have a general policy of > objecting to any new use of TASK_SIZE. If you really really need to depend on > 32-bitness in new code, please figure out what exactly you mean by “32-bit” > and use an explicit check. The explicit check would be: test_thread_flag(TIF_ADDR32) ? IA32_PAGE_OFFSET : TASK_SIZE_MAX which is the same as TASK_SIZE. Or, do we want a new macro? #define IBT_BITMAP_SIZE (test_thread_flag(TIF_ADDR32) ? \ (IA32_PAGE_OFFSET / PAGE_SIZE / BITS_PER_BYTE) : \ (TASK_SIZE_MAX / PAGE_SIZE / BITS_PER_BYTE)) Yu-cheng