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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 AD0A7C43461 for ; Thu, 22 Apr 2021 16:55:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 75455613F6 for ; Thu, 22 Apr 2021 16:55:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238220AbhDVQ40 (ORCPT ); Thu, 22 Apr 2021 12:56:26 -0400 Received: from foss.arm.com ([217.140.110.172]:53868 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238156AbhDVQ4Y (ORCPT ); Thu, 22 Apr 2021 12:56:24 -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 076B311D4; Thu, 22 Apr 2021 09:55:49 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.22.241]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 73A843F694; Thu, 22 Apr 2021 09:55:47 -0700 (PDT) Date: Thu, 22 Apr 2021 17:55:45 +0100 From: Mark Rutland To: He Zhe Cc: oleg@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, paul@paul-moore.com, eparis@redhat.com, linux-audit@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] arm64: syscall.h: Add sign extension handling in syscall_get_return_value for compat Message-ID: <20210422165545.GE66392@C02TD0UTHF1T.local> References: <20210416075533.7720-1-zhe.he@windriver.com> <20210416075533.7720-2-zhe.he@windriver.com> <20210421174105.GB52940@C02TD0UTHF1T.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210421174105.GB52940@C02TD0UTHF1T.local> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 21, 2021 at 06:41:05PM +0100, Mark Rutland wrote: > On Fri, Apr 16, 2021 at 03:55:32PM +0800, He Zhe wrote: > > Add sign extension handling in syscall_get_return_value so that it can > > handle 32-bit compatible case and can be used by for example audit, just > > like what syscall_get_error does. > > If a compat syscall can ever legitimately return a non-error value with > bit 31 set, and this sign-extends it, is that ever going to reach > userspace as a 64-bit value? > > IIUC things like mmap() can return pointers above 2GiB for a compat > task, so I'm a bit uneasy that we'd handle those wrong. I can't see a > way of preventing that unless we keep the upper 32 bits for errors. Looking at this with fresh eyes, I think we can more closely mirror syscall_get_error(), and do something like: static inline long syscall_get_return_value(struct task_struct *task, struct pt_regs *regs) { long val = regs->regs[0]; long error = val; if (is_compat_thread(task_thread_info(task))) error = sign_extend64(error, 31); return IS_ERR_VALUE(error) ? error : val; } Thanks, Mark. > > Mark. > > > > > Signed-off-by: He Zhe > > --- > > arch/arm64/include/asm/syscall.h | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h > > index cfc0672013f6..cd7a22787aeb 100644 > > --- a/arch/arm64/include/asm/syscall.h > > +++ b/arch/arm64/include/asm/syscall.h > > @@ -44,7 +44,12 @@ static inline long syscall_get_error(struct task_struct *task, > > static inline long syscall_get_return_value(struct task_struct *task, > > struct pt_regs *regs) > > { > > - return regs->regs[0]; > > + long val = regs->regs[0]; > > + > > + if (is_compat_thread(task_thread_info(task))) > > + val = sign_extend64(val, 31); > > + > > + return val; > > } > > > > static inline void syscall_set_return_value(struct task_struct *task, > > -- > > 2.17.1 > >