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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD733C433F5 for ; Fri, 19 Nov 2021 13:44:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A319061A8A for ; Fri, 19 Nov 2021 13:44:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235555AbhKSNri (ORCPT ); Fri, 19 Nov 2021 08:47:38 -0500 Received: from foss.arm.com ([217.140.110.172]:51786 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235424AbhKSNrh (ORCPT ); Fri, 19 Nov 2021 08:47:37 -0500 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 602696D; Fri, 19 Nov 2021 05:44:35 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 79E883F70D; Fri, 19 Nov 2021 05:44:34 -0800 (PST) Date: Fri, 19 Nov 2021 13:44:32 +0000 From: Mark Rutland To: Will Deacon Cc: Vincent Whitchurch , catalin.marinas@arm.com, kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: uaccess: fix put_user() with TTBR0 PAN Message-ID: <20211119134432.GB25912@lakrids.cambridge.arm.com> References: <20211118163417.21617-1-vincent.whitchurch@axis.com> <20211119113306.GA13292@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211119113306.GA13292@willie-the-truck> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 19, 2021 at 11:33:06AM +0000, Will Deacon wrote: > On Thu, Nov 18, 2021 at 05:34:17PM +0100, Vincent Whitchurch wrote: > > The value argument to put_user() must be evaluated before the TTBR0 > > switch is done. Otherwise, if it is a function and the function sleeps, > > the reserved TTBR0 will be restored when the process is switched in > > again and the process will end up in an infinite loop of faults. > > > > This problem was seen with the put_user() in schedule_tail(). A similar > > fix was done for RISC-V in commit 285a76bb2cf51b0c74c634 ("riscv: > > evaluate put_user() arg before enabling user access"). > > > > Fixes: f253d827f33cb5a5990 ("arm64: uaccess: refactor __{get,put}_user") > > Signed-off-by: Vincent Whitchurch > > --- > > arch/arm64/include/asm/uaccess.h | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > > index 6e2e0b7031ab..96b26fa9d3d0 100644 > > --- a/arch/arm64/include/asm/uaccess.h > > +++ b/arch/arm64/include/asm/uaccess.h > > @@ -362,10 +362,11 @@ do { \ > > #define __put_user_error(x, ptr, err) \ > > do { \ > > __typeof__(*(ptr)) __user *__p = (ptr); \ > > + __typeof__(*(__p)) __val = (x); \ > > might_fault(); \ > > if (access_ok(__p, sizeof(*__p))) { \ > > __p = uaccess_mask_ptr(__p); \ > > - __raw_put_user((x), __p, (err)); \ > > + __raw_put_user(__val, __p, (err)); \ > > } else { \ > > (err) = -EFAULT; \ > > } \ > > > Oh, nice spot! I hope you didn't lose too much time debugging if you > actually ran into this... > > Although it seems a lot less likely to cause a problem, should we do > something similar for __get_user_error() and assign to (x) outside of > the uaccess-disabled section? I agree we should follow up with a more general cleanup to avoid any macro evaluation within user-access or tco critical sections. Since that's especially subtle for the get_*() helpers (and I beleive there may be some other latent issues in that area), I reckon we should do that as a follow-up, and shouldn't block this patch on that being done. I'll go audit that and see what I spot. Thanks, Mark.