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 3C4A2C43334 for ; Tue, 7 Jun 2022 21:33:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1379878AbiFGVd1 (ORCPT ); Tue, 7 Jun 2022 17:33:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1381188AbiFGVbo (ORCPT ); Tue, 7 Jun 2022 17:31:44 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 719D922CEC4; Tue, 7 Jun 2022 12:04:06 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 0571D6184B; Tue, 7 Jun 2022 19:04:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11BCEC385A2; Tue, 7 Jun 2022 19:04:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1654628645; bh=mmgUOoWsvmyCloJOJysj77fpGdpLejOlNk4+m0u4eXA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NiNZ2ceDGGPtn6RU7znjtUkH1aU24+8evayYWB2ZVr+6k+fvRwxcxBd/OEvycqa3K dm/pc0g5CyU1RYZLAtBNZ70N51ZOe6Ig81ldd4m/lYm+1pQc32C3GHMV7mdirC587b YNc/9vafk0hfvB8Ko1aIi0eDtXWF3bFsrYhf+5ng= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mark Rutland , Alexander Popov , Andrew Morton , Andy Lutomirski , Catalin Marinas , Kees Cook , Will Deacon , Sasha Levin Subject: [PATCH 5.18 403/879] arm64: stackleak: fix current_top_of_stack() Date: Tue, 7 Jun 2022 18:58:41 +0200 Message-Id: <20220607165014.560134923@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220607165002.659942637@linuxfoundation.org> References: <20220607165002.659942637@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Mark Rutland [ Upstream commit e85094c31ddb794ac41c299a5a7a68243148f829 ] Due to some historical confusion, arm64's current_top_of_stack() isn't what the stackleak code expects. This could in theory result in a number of problems, and practically results in an unnecessary performance hit. We can avoid this by aligning the arm64 implementation with the x86 implementation. The arm64 implementation of current_top_of_stack() was added specifically for stackleak in commit: 0b3e336601b82c6a ("arm64: Add support for STACKLEAK gcc plugin") This was intended to be equivalent to the x86 implementation, but the implementation, semantics, and performance characteristics differ wildly: * On x86, current_top_of_stack() returns the top of the current task's task stack, regardless of which stack is in active use. The implementation accesses a percpu variable which the x86 entry code maintains, and returns the location immediately above the pt_regs on the task stack (above which x86 has some padding). * On arm64 current_top_of_stack() returns the top of the stack in active use (i.e. the one which is currently being used). The implementation checks the SP against a number of potentially-accessible stacks, and will BUG() if no stack is found. The core stackleak_erase() code determines the upper bound of stack to erase with: | if (on_thread_stack()) | boundary = current_stack_pointer; | else | boundary = current_top_of_stack(); On arm64 stackleak_erase() is always called on a task stack, and on_thread_stack() should always be true. On x86, stackleak_erase() is mostly called on a trampoline stack, and is sometimes called on a task stack. Currently, this results in a lot of unnecessary code being generated for arm64 for the impossible !on_thread_stack() case. Some of this is inlined, bloating stackleak_erase(), while portions of this are left out-of-line and permitted to be instrumented (which would be a functional problem if that code were reachable). As a first step towards improving this, this patch aligns arm64's implementation of current_top_of_stack() with x86's, always returning the top of the current task's stack. With GCC 11.1.0 this results in the bulk of the unnecessary code being removed, including all of the out-of-line instrumentable code. While I don't believe there's a functional problem in practice I've marked this as a fix since the semantic was clearly wrong, the fix itself is simple, and other code might rely upon this in future. Fixes: 0b3e336601b82c6a ("arm64: Add support for STACKLEAK gcc plugin") Signed-off-by: Mark Rutland Cc: Alexander Popov Cc: Andrew Morton Cc: Andy Lutomirski Cc: Catalin Marinas Cc: Kees Cook Cc: Will Deacon Acked-by: Catalin Marinas Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220427173128.2603085-2-mark.rutland@arm.com Signed-off-by: Sasha Levin --- arch/arm64/include/asm/processor.h | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 73e38d9a540c..6b1a12c23fe7 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -381,12 +381,10 @@ long get_tagged_addr_ctrl(struct task_struct *task); * of header definitions for the use of task_stack_page. */ -#define current_top_of_stack() \ -({ \ - struct stack_info _info; \ - BUG_ON(!on_accessible_stack(current, current_stack_pointer, 1, &_info)); \ - _info.high; \ -}) +/* + * The top of the current task's task stack + */ +#define current_top_of_stack() ((unsigned long)current->stack + THREAD_SIZE) #define on_thread_stack() (on_task_stack(current, current_stack_pointer, 1, NULL)) #endif /* __ASSEMBLY__ */ -- 2.35.1