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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E01A4C1975A for ; Tue, 17 Mar 2020 17:48:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C24C920735 for ; Tue, 17 Mar 2020 17:48:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726278AbgCQRsM (ORCPT ); Tue, 17 Mar 2020 13:48:12 -0400 Received: from foss.arm.com ([217.140.110.172]:41012 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbgCQRsM (ORCPT ); Tue, 17 Mar 2020 13:48:12 -0400 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 D8A3A31B; Tue, 17 Mar 2020 10:48:11 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E2EB63F67D; Tue, 17 Mar 2020 10:48:08 -0700 (PDT) Date: Tue, 17 Mar 2020 17:48:06 +0000 From: Catalin Marinas To: Vincenzo Frascino Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, linux-mips@vger.kernel.org, x86@kernel.org, Will Deacon , Arnd Bergmann , Russell King , Paul Burton , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , Borislav Petkov , Stephen Boyd , Mark Salyzyn , Kees Cook , Peter Collingbourne , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nick Desaulniers , Marc Zyngier , Mark Rutland , Will Deacon Subject: Re: [PATCH v4 18/26] arm64: vdso32: Replace TASK_SIZE_32 check in vgettimeofday Message-ID: <20200317174806.GE632169@arrakis.emea.arm.com> References: <20200317122220.30393-1-vincenzo.frascino@arm.com> <20200317122220.30393-19-vincenzo.frascino@arm.com> <20200317143834.GC632169@arrakis.emea.arm.com> <20200317155031.GD632169@arrakis.emea.arm.com> <83aaf9e1-0a8f-4908-577a-23766541b2ba@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <83aaf9e1-0a8f-4908-577a-23766541b2ba@arm.com> Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Tue, Mar 17, 2020 at 04:40:48PM +0000, Vincenzo Frascino wrote: > On 3/17/20 3:50 PM, Catalin Marinas wrote: > > On Tue, Mar 17, 2020 at 03:04:01PM +0000, Vincenzo Frascino wrote: > >> On 3/17/20 2:38 PM, Catalin Marinas wrote: > >>> On Tue, Mar 17, 2020 at 12:22:12PM +0000, Vincenzo Frascino wrote: > >> > >> Can TASK_SIZE > UINTPTR_MAX on an arm64 system? > > > > TASK_SIZE yes on arm64 but not TASK_SIZE_32. I was asking about the > > arm32 check where TASK_SIZE < UINTPTR_MAX. How does the vdsotest return > > -EFAULT on arm32? Which code path causes this in the user vdso code? > > Sorry I got confused because you referred to arch/arm/vdso/vgettimeofday.c which > is the arm64 implementation, not the compat one :) You figured out (in your subsequent reply) that I was indeed talking about arm32 ;). > In the case of arm32 everything is handled via syscall fallback. So clock_gettime() on arm32 always falls back to the syscall? > > My guess is that on arm32 it only fails with -EFAULT in the syscall > > fallback path since a copy_to_user() would fail the access_ok() check. > > Does it always take the fallback path if ts > TASK_SIZE? > > Correct, it goes via fallback. The return codes for these syscalls are specified > by the ABI [1]. Then I agree with you the way on which arm32 achieves it should > be via access_ok() check. "it should be" or "it is" on arm32? If, on arm32, clock_gettime() is (would be?) handled in the vdso entirely, who checks for the pointer outside the accessible address space (as per the clock_gettime man page)? I'm fine with such check as long as it is consistent across arm32 and arm64 compat. Or even on arm64 native between syscall fallback and vdso execution. I haven't figured out yet whether this is the case. > >>> This last check needs an explanation. If the clock_id is invalid but res > >>> is not NULL, we allow it. I don't see where the compatibility issue is, > >>> arm32 doesn't have such check. > >> > >> The case that you are describing has to return -EPERM per ABI spec. This case > >> has to return -EINVAL. > >> > >> The first case is taken care from the generic code. But if we don't do this > >> check before on arm64 compat we end up returning the wrong error code. > > > > I guess I have the same question as above. Where does the arm32 code > > return -EINVAL for that case? Did it work correctly before you removed > > the TASK_SIZE_32 check? > > I repeated the test and seems that it was failing even before I removed > TASK_SIZE_32. For reasons I can't explain I did not catch it before. > > The getres syscall should return -EINVAL in the cases specified in [1]. It states 'clk_id specified is not supported on this system'. Fair enough but it doesn't say that it returns -EINVAL only if res == NULL. You also don't explain why __cvdso_clock_getres_time32() doesn't already detect an invalid clk_id on arm64 compat (but does it on arm32). -- Catalin