From patchwork Thu Nov 20 05:13:04 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: AKASHI Takahiro X-Patchwork-Id: 5345741 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 103BB9F2F1 for ; Thu, 20 Nov 2014 05:15:34 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 26A56201FA for ; Thu, 20 Nov 2014 05:15:33 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4540D20176 for ; Thu, 20 Nov 2014 05:15:32 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1XrK3j-0004JU-Vr; Thu, 20 Nov 2014 05:13:35 +0000 Received: from mail-pd0-f181.google.com ([209.85.192.181]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1XrK3i-0004Fi-9v for linux-arm-kernel@lists.infradead.org; Thu, 20 Nov 2014 05:13:34 +0000 Received: by mail-pd0-f181.google.com with SMTP id z10so2310550pdj.26 for ; Wed, 19 Nov 2014 21:13:12 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=if/d2w+KOhqtOlwpVUkudfdAw1IVxUuvbNBs+abDcPI=; b=JErAhBdTyjwaklC98y6crw5NmMpkGV2yEqC65LsKpkj8pNYIt5yI1Pv06diC4Iv4jf YtQgzddAYfYrzz9C6JJb8q2yFqkc0QnodoN/R0aTxRA5RiLXWhfNuGmTjuhKXToUGQsn nrFqgJ6zHPold/lfR9RPAUXoxGqyxh5c93qZzqBnugME9hKa/QxOKqg6ww88FLWaZiaA +rv2ZopPVPgfbxEMfQGpaArWSXznUW9QsylpAdjBePljrxT2RdhnKjv5sMCqrpMjeT2K xydK6fs34wwikWHpxSXVs+9Qdy70OX4SZ5eQ5MK/2aRx54O8hKHZeenqgr9L7kYCpiH4 tcTg== X-Gm-Message-State: ALoCoQniKLjuK+eM7FnLT3d2sXQzOG4UYt+9haS2c/gYHqtLpzDlXliBTXZ7CCTTj/hQHFDdMk2g X-Received: by 10.66.248.104 with SMTP id yl8mr52805655pac.2.1416460392453; Wed, 19 Nov 2014 21:13:12 -0800 (PST) Received: from [192.168.1.157] (KD182249097096.au-net.ne.jp. [182.249.97.96]) by mx.google.com with ESMTPSA id aq1sm803357pbd.29.2014.11.19.21.13.06 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 19 Nov 2014 21:13:11 -0800 (PST) Message-ID: <546D7860.2010300@linaro.org> Date: Thu, 20 Nov 2014 14:13:04 +0900 From: AKASHI Takahiro User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Will Deacon Subject: Re: [PATCH v8 2/6] arm64: ptrace: allow tracer to skip a system call References: <1416273038-15590-1-git-send-email-takahiro.akashi@linaro.org> <1416273038-15590-3-git-send-email-takahiro.akashi@linaro.org> <20141118140425.GM18842@arm.com> <546C58DB.5080204@linaro.org> <20141119190601.GM15985@arm.com> In-Reply-To: <20141119190601.GM15985@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20141119_211334_366878_F8C52B59 X-CRM114-Status: GOOD ( 18.68 ) X-Spam-Score: -0.7 (/) Cc: "linaro-kernel@lists.linaro.org" , "keescook@chromium.org" , Catalin Marinas , "arndb@arndb.de" , "linux-kernel@vger.kernel.org" , "dsaxena@linaro.org" , "linux-arm-kernel@lists.infradead.org" X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_LOW, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 11/20/2014 04:06 AM, Will Deacon wrote: > On Wed, Nov 19, 2014 at 08:46:19AM +0000, AKASHI Takahiro wrote: >> On 11/18/2014 11:04 PM, Will Deacon wrote: >>> On Tue, Nov 18, 2014 at 01:10:34AM +0000, AKASHI Takahiro wrote: >>>> >>>> + if (((int)regs->syscallno == -1) && (orig_syscallno == -1)) { >>>> + /* >>>> + * user-issued syscall(-1): >>>> + * RESTRICTION: We always return ENOSYS whatever value is >>>> + * stored in x0 (a return value) at this point. >>>> + * Normally, with ptrace off, syscall(-1) returns -ENOSYS. >>>> + * With ptrace on, however, if a tracer didn't pay any >>>> + * attention to user-issued syscall(-1) and just let it go >>>> + * without a hack here, it would return a value in x0 as in >>>> + * other system call cases. This means that this system call >>>> + * might succeed and see any bogus return value. >>>> + * This should be definitely avoided. >>>> + */ >>>> + regs->regs[0] = -ENOSYS; >>>> + } >>> >>> I'm still really uncomfortable with this, and it doesn't seem to match what >>> arch/arm/ does either. >> >> Yeah, I know but >> as I mentioned before, syscall(-1) will be signaled on arm, and so we don't >> have to care about a return value :) > > What does x86 do? On x86, syscall(-1) returns -ENOSYS if not traced, and we can change a return value if traced. >>> Doesn't it also prevent a tracer from skipping syscall(-1)? >> >> Syscall(-1) will return -ENOSYS whether or not a syscallno is explicitly >> replaced with -1 by a tracer, and, in this sense, it is *skipped*. > > Ok, but now userspace sees -ENOSYS for a skipped system call in that case, > whereas it would usually see whatever the trace put in x0, right? Yes. If you don't really like this behavior, how about this patch instead of my [2/6] patch? With this change, I believe, syscall(-1) returns -ENOSYS by default whether traced or not, and still you can change a return value when tracing. (But a drawback here is that a tracer will see -ENOSYS in x0 even at syscall entry for syscall(-1).) -Takahiro AKASHI > Will > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 726b910..1ef57d0 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -668,8 +668,15 @@ ENDPROC(el0_svc) * switches, and waiting for our parent to respond. */ __sys_trace: + cmp w8, #-1 // default errno for invalid + b.ne 1f // system call + mov x0, #-ENOSYS + str x0, [sp, #S_X0] +1: mov x0, sp bl syscall_trace_enter + cmp w0, #-1 // skip the syscall? + b.eq __sys_trace_return_skipped adr lr, __sys_trace_return // return address uxtw scno, w0 // syscall number (possibly new) mov x1, sp // pointer to regs @@ -684,6 +691,7 @@ __sys_trace: __sys_trace_return: str x0, [sp] // save returned x0 +__sys_trace_return_skipped: mov x0, sp bl syscall_trace_exit b ret_to_user