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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 75FB8C433F5 for ; Tue, 4 Jan 2022 10:42:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=pMrA7OzP8t4nYwMh7SIYk2YrnpQlV4KTQElSbJgT6kI=; b=A05TCJpp2kWKBV l1aASCrpErZsKZzCOdr+V9pEzDNm3DTh/Rmx56jRNse3X2okRNTJqUU9bJm+tXboDs6XgjVXDENns /4q4cIxSpcVxu+Pq1Xq3v/I//iJPplhVRszcUmExBd7MOLq8VcJq2v2R//YQyWua1NM5NCsd6mhkD gNK9MALQH7B90CH1EFKf0V+Mj7me/5eFRfQWMKoVwT9q7KSJTAlOsu2SXqkZnJToWViCdn65aRM2A W1NJI0DWTRjvEfDm4oLB95w9e3FpjtVjfYVRBJTgW3mXdqe70d8i9+LAWkdmcfhxR0WwCRzkGIaEL 5nihWvZbnmbkMrx6sN5Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n4hFY-00BAtQ-Oo; Tue, 04 Jan 2022 10:41:04 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1n4hFV-00BAsj-LU for linux-arm-kernel@lists.infradead.org; Tue, 04 Jan 2022 10:41:03 +0000 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 043871FB; Tue, 4 Jan 2022 02:41:00 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.9.1]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 20FF33F5A1; Tue, 4 Jan 2022 02:40:57 -0800 (PST) Date: Tue, 4 Jan 2022 10:40:51 +0000 From: Mark Rutland To: Dan Li Cc: catalin.marinas@arm.com, will@kernel.org, samitolvanen@google.com, maz@kernel.org, joey.gouly@arm.com, pcc@google.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] [RFC] aarch64: scs: reload shadow call stack in user exception entry Message-ID: References: <20211228010604.109572-1-ashimida@linux.alibaba.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211228010604.109572-1-ashimida@linux.alibaba.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220104_024101_775964_00796FD5 X-CRM114-Status: GOOD ( 20.91 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On Mon, Dec 27, 2021 at 05:06:04PM -0800, Dan Li wrote: > When el0 exception occurs, kernel_entry/exit will load/save tsk->scs_sp > to ensure scs working properly. AFAIK, the SCS offset should always be > 0 at this time. > > Is it reasonable to reload x18 to scs_base directly in kernel_entry > here, or am I missing something? > > Signed-off-by: Dan Li AFAICT the saving here is just that we avoid storing the SCS SP upon return to EL0, and I suspect that in practice that's not measureable. So without numbers to show otherwise, I'd prefer to leave this as-is, though I agree that this patch should work. If we do want to change this, I think we need a comment in the `kernel_exit` path to pair with the `scs_load` in `kernel_entry`. Thanks, Mark. > --- > arch/arm64/include/asm/scs.h | 7 +++++++ > arch/arm64/kernel/entry.S | 3 +-- > 2 files changed, 8 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/scs.h b/arch/arm64/include/asm/scs.h > index 8297bccf0784..2bc0d0575e75 100644 > --- a/arch/arm64/include/asm/scs.h > +++ b/arch/arm64/include/asm/scs.h > @@ -9,6 +9,10 @@ > #ifdef CONFIG_SHADOW_CALL_STACK > scs_sp .req x18 > > + .macro scs_reload tsk > + ldr scs_sp, [\tsk, #TSK_TI_SCS_BASE] > + .endm > + > .macro scs_load tsk > ldr scs_sp, [\tsk, #TSK_TI_SCS_SP] > .endm > @@ -17,6 +21,9 @@ > str scs_sp, [\tsk, #TSK_TI_SCS_SP] > .endm > #else > + .macro scs_reload tsk > + .endm > + > .macro scs_load tsk > .endm > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index bc6d5a970a13..57547a3e4f7c 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -265,7 +265,7 @@ alternative_if ARM64_HAS_ADDRESS_AUTH > alternative_else_nop_endif > 1: > > - scs_load tsk > + scs_reload tsk > .else > add x21, sp, #PT_REGS_SIZE > get_current_task tsk > @@ -365,7 +365,6 @@ alternative_if ARM64_WORKAROUND_845719 > alternative_else_nop_endif > #endif > 3: > - scs_save tsk > > /* Ignore asynchronous tag check faults in the uaccess routines */ > ldr x0, [tsk, THREAD_SCTLR_USER] > -- > 2.17.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel