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 X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 262BDC4742C for ; Fri, 13 Nov 2020 12:50:23 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9ED752224B for ; Fri, 13 Nov 2020 12:50:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Bx50a8XR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9ED752224B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:MIME-Version:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:References:In-Reply-To:Message-Id:Date:Subject:To: From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Rp1H7IAI6/P0hJRHJnUqwe+dBemQGyaRnuXM3H8nZlA=; b=Bx50a8XRumRvrYJVVPaAIGfY67 /sB0pxGpPDO/ky0OjHGPtij44Awn3Zx3us6GigsD4praAqjpxoVCFfb0N+Wb3JnX7m/Fdv5B3Jk5H P7X/JYX8Y+jRUB6sYjSuCC8mEs1ybHGkjUqGFt4t7AGBW83P1LgyKJdEhQRimNwI0SIxXpInFDYWo kt4/QlJLTdfScXN/nuwNndqS8BMwgRPHTH1Yc+QUr2qvnASFUCUw0PwLEU0XQAlHOUeACQ2+NnBjp B314jgGUiW6PpKQIMSk265XeP10mi3y3ArQbn3D//O55OREV0qg81z0YgTxF1kv8FRXQjhYZT3lZf mHmgeFTQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kdYWU-0006BG-AR; Fri, 13 Nov 2020 12:49:50 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kdYWQ-0006AD-MS for linux-arm-kernel@lists.infradead.org; Fri, 13 Nov 2020 12:49:47 +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 39EB714BF; Fri, 13 Nov 2020 04:49:45 -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 ESMTPA id 3A9403F6CF; Fri, 13 Nov 2020 04:49:44 -0800 (PST) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org Subject: [PATCHv4 01/17] arm64: ensure ERET from kthread is illegal Date: Fri, 13 Nov 2020 12:49:21 +0000 Message-Id: <20201113124937.20574-2-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20201113124937.20574-1-mark.rutland@arm.com> References: <20201113124937.20574-1-mark.rutland@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201113_074946_796699_8C835080 X-CRM114-Status: GOOD ( 15.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, robin.murphy@arm.com, james.morse@arm.com, hch@lst.de MIME-Version: 1.0 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 For consistency, all tasks have a pt_regs reserved at the highest portion of their task stack. Among other things, this ensures that a task's SP is always pointing within its stack rather than pointing immediately past the end. While it is never legitimate to ERET from a kthread, we take pains to initialize pt_regs for kthreads as if this were legitimate. As this is never legitimate, the effects of an erroneous return are rarely tested. Let's simplify things by initializing a kthread's pt_regs such that an ERET is caught as an illegal exception return, and removing the explicit initialization of other exception context. Note that as spectre_v4_enable_task_mitigation() only manipulates the PSTATE within the unused regs this is safe to remove. As user tasks will have their exception context initialized via start_thread() or start_compat_thread(), this should only impact cases where something has gone very wrong and we'd like that to be clearly indicated. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Christoph Hellwig Cc: James Morse Cc: Will Deacon --- arch/arm64/kernel/process.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 4784011cecac..855137daafbf 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -422,16 +422,15 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, if (clone_flags & CLONE_SETTLS) p->thread.uw.tp_value = tls; } else { + /* + * A kthread has no context to ERET to, so ensure any buggy + * ERET is treated as an illegal exception return. + * + * When a user task is created from a kthread, childregs will + * be initialized by start_thread() or start_compat_thread(). + */ memset(childregs, 0, sizeof(struct pt_regs)); - childregs->pstate = PSR_MODE_EL1h; - if (IS_ENABLED(CONFIG_ARM64_UAO) && - cpus_have_const_cap(ARM64_HAS_UAO)) - childregs->pstate |= PSR_UAO_BIT; - - spectre_v4_enable_task_mitigation(p); - - if (system_uses_irq_prio_masking()) - childregs->pmr_save = GIC_PRIO_IRQON; + childregs->pstate = PSR_MODE_EL1h | PSR_IL_BIT; p->thread.cpu_context.x19 = stack_start; p->thread.cpu_context.x20 = stk_sz; -- 2.11.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel