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 49D2AC433EF for ; Mon, 25 Apr 2022 11:57:35 +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:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ihCC+6PU9263rtuiEtGLVhjmiHbczk3W7XfTWjTKCYo=; b=f0MRWf3J018IPn /Rk0sO+ItgRj/nsYCBPhKmklHy6DtfV35Vu5EwjH6fDfberCuYCDtMi2CHqL9v6he+zuu8EuCMkat f98jroAT3z036YGSetHLHQe1fZLcyDkrwOZAi3JAeEy4k5fDx0vurqvopYljOA2F/uA9WTB1nTl0U 8RxX7f1TfXZ1gx5V5I4mfWqg9oWdERHI5kc78pSzOqv9MzUcZgjBGeb2KASVrVw6MiCOh6MwzM8dk Iw1JMjMYGh4pLWn4EmNSDCB1Zj00qvGizmdEi+t5lvcyIg80TTTWu9BnHFIM7cxsXMEE2nCbBAa/c upWCt9Q6xXNx+UaCGUeA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nixKN-009NsG-Ao; Mon, 25 Apr 2022 11:56:28 +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 1nixKA-009NoI-5Z for linux-arm-kernel@lists.infradead.org; Mon, 25 Apr 2022 11:56:16 +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 EDF77ED1; Mon, 25 Apr 2022 04:56:12 -0700 (PDT) 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 ESMTPA id B14D83F73B; Mon, 25 Apr 2022 04:56:11 -0700 (PDT) From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, alex.popov@linux.com, catalin.marinas@arm.com, keescook@chromium.org, linux-arm-kernel@lists.infradead.org, luto@kernel.org, mark.rutland@arm.com, will@kernel.org Subject: [PATCH 1/8] arm64: stackleak: fix current_top_of_stack() Date: Mon, 25 Apr 2022 12:55:56 +0100 Message-Id: <20220425115603.781311-2-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220425115603.781311-1-mark.rutland@arm.com> References: <20220425115603.781311-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220425_045614_337574_708F07D9 X-CRM114-Status: GOOD ( 18.73 ) 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 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 --- 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 73e38d9a540ce..6b1a12c23fe77 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__ */ -- 2.30.2 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel