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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6A2C0C4332F for ; Fri, 9 Dec 2022 15:01:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229561AbiLIPBI (ORCPT ); Fri, 9 Dec 2022 10:01:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230203AbiLIPAe (ORCPT ); Fri, 9 Dec 2022 10:00:34 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B04C4813B6 for ; Fri, 9 Dec 2022 07:00:15 -0800 (PST) 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 41C2323A; Fri, 9 Dec 2022 07:00:22 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.41.252]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7C9003F73D; Fri, 9 Dec 2022 07:00:14 -0800 (PST) Date: Fri, 9 Dec 2022 15:00:11 +0000 From: Mark Rutland To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, linux-efi@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com Subject: Re: [PATCH] arm64: efi: Account for the EFI runtime stack in stack unwinder Message-ID: References: <20221209133414.3330761-1-ardb@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org On Fri, Dec 09, 2022 at 03:46:48PM +0100, Ard Biesheuvel wrote: > On Fri, 9 Dec 2022 at 15:37, Mark Rutland wrote: > > > > On Fri, Dec 09, 2022 at 02:34:14PM +0100, Ard Biesheuvel wrote: > > > The EFI runtime services run from a dedicated stack now, and so the > > > stack unwinder needs to be informed about this. > > > > > > Signed-off-by: Ard Biesheuvel > > > --- > > > > > > I realised while looking into this that comparing current_work() against > > > efi_rts_work.work is not sufficient to decide whether current is running > > > EFI code, given that the ACPI subsystem will call efi_call_virt_pointer() > > > directly. > > > > > > So instead, we can check whether the stashed thread stack pointer value > > > matches current's thread stack if the EFI runtime stack is currently in > > > use: > > > > > > #define current_in_efi() \ > > > (!preemptible() && spin_is_locked(&efi_rt_lock) && \ > > > on_task_stack(current, efi_rt_stack_top[-1], 1)) > > > > Unless you're overwriting task_struct::stack (which seems scary to me), that > > doesn't look right; on_task_stack() checks whether a given base + size is on > > the stack allocated for the task (i.e. task_struct::stack + THREAD_SIZE), not > > the stack the task is currently using. > > > > Note the [-1]. > > efi_rt_stack_top[-1] contains the value the stack pointer had before > switching to the EFI runtime stack. If that value is an address > covered by current's thread stack, current must be the task that has a > live call frame inside the EFI code at the time the call stack is > captured. Ah, I had missed that subtlety. Would you mind if we add that first sentence as a comment for that code, i.e. | /* | * efi_rt_stack_top[-1] contains the value the stack pointer had before | * switching to the EFI runtime stack. | */ | #define current_in_efi() \ | (!preemptible() && spin_is_locked(&efi_rt_lock) && \ | on_task_stack(current, efi_rt_stack_top[-1], 1)) ... that way when I look at this in 3 to 6 months time I won't fall into the same trap. :) I assume that the EFI trampoline code clobbers the value on the way out so it doesn't spruriously match later. > > I would expect this to be something like: > > > > #define current_in_efi() \ > > (!preemptible() && spin_is_locked(&efi_rt_lock) && \ > > stackinfo_on_stack(stackinfo_get_efi(), current_stack_pointer, 1)) > > > > ... or an inline function given this is sufficiently painful as a macro. > > current_stack_pointer is the actual value of SP at the time this code > is called. So if we are unwinding from a sync exception taken while > handling an IRQ that arrived while running the EFI code, that SP value > has nothing to do with the EFI stack. Yes, good point. > > ... unless I've confused myself? > > > > I think you might have ... :-) :) Mark.