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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A7DB0C0044D for ; Mon, 16 Mar 2020 14:43:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 884F720736 for ; Mon, 16 Mar 2020 14:43:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731560AbgCPOny (ORCPT ); Mon, 16 Mar 2020 10:43:54 -0400 Received: from foss.arm.com ([217.140.110.172]:49640 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731551AbgCPOnx (ORCPT ); Mon, 16 Mar 2020 10:43:53 -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 EA63E1FB; Mon, 16 Mar 2020 07:43:52 -0700 (PDT) Received: from mbp (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C84B43F52E; Mon, 16 Mar 2020 07:43:49 -0700 (PDT) Date: Mon, 16 Mar 2020 14:43:47 +0000 From: Catalin Marinas To: Vincenzo Frascino Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, clang-built-linux@googlegroups.com, 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 v3 18/26] arm64: Introduce asm/vdso/processor.h Message-ID: <20200316144346.GF3005@mbp> References: <20200313154345.56760-1-vincenzo.frascino@arm.com> <20200313154345.56760-19-vincenzo.frascino@arm.com> <20200315182950.GB32205@mbp> <20200316103437.GD3005@mbp> <77a2e91a-58f4-3ba3-9eef-42d6a8faf859@arm.com> <20200316112205.GE3005@mbp> <9a0a9285-8a45-4f65-3a83-813cabd0f0d3@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a0a9285-8a45-4f65-3a83-813cabd0f0d3@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Mon, Mar 16, 2020 at 01:35:17PM +0000, Vincenzo Frascino wrote: > On 3/16/20 11:22 AM, Catalin Marinas wrote: > > As I said above, I don't see how removing 'if ((u32)ts >= (1UL << 32))' > > makes any difference. This check was likely removed by the compiler > > already. > > > > Also, userspace doesn't have a trivial way to figure out TASK_SIZE and I > > can't see anything that tests this in the vdsotest (though I haven't > > spent that much time looking). If it's hard-coded, note that arm32 > > TASK_SIZE is different from TASK_SIZE_32 on arm64. > > > > Can you tell what actually is failing in vdsotest if you remove the > > TASK_SIZE_32 checks in the arm64 compat vdso? > > To me does not seem optimized out. Which version of the compiler are you using? I misread the #ifdef'ery in asm/processor.h. So with 4K pages, TASK_SIZE_32 is (1UL<<32)-PAGE_SIZE. However, with 64K pages _and_ CONFIG_KUSER_HELPERS, TASK_SIZE_32 is 1UL<<32 and the check is removed by the compiler. With the 4K build, __vdso_clock_gettime starts as: 00000194 <__vdso_clock_gettime>: 194: f511 5f80 cmn.w r1, #4096 ; 0x1000 198: d214 bcs.n 1c4 <__vdso_clock_gettime+0x30> 19a: b5b0 push {r4, r5, r7, lr} ... 1c4: f06f 000d mvn.w r0, #13 1c8: 4770 bx lr With 64K pages: 00000194 <__vdso_clock_gettime>: 194: b5b0 push {r4, r5, r7, lr} ... 1be: bdb0 pop {r4, r5, r7, pc} I haven't tried but it's likely that the vdsotest fails with 64K pages and compat enabled (requires EXPERT). > Please find below the list of errors for clock_gettime (similar for the other): > > passing UINTPTR_MAX to clock_gettime (VDSO): terminated by unexpected signal 7 > clock-gettime-monotonic/abi: 1 failures/inconsistencies encountered Ah, so it uses UINTPTR_MAX in the test. Fair enough but I don't think the arm64 check is entirely useful. On arm32, the check was meant to return -EFAULT for addresses beyond TASK_SIZE that may enter into the kernel or module space. On arm64 compat, the kernel space is well above the reach of the 32-bit code. If you want to preserve some compatibility for this specific test, what about checking for wrapping around 0, I think it would make more sense. Something like: if ((u32)ts > UINTPTR_MAX - sizeof(*ts) + 1) -- Catalin