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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 B99DFC76188 for ; Mon, 22 Jul 2019 07:48:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 922232199C for ; Mon, 22 Jul 2019 07:48:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563781724; bh=H5CHHV0UF6FlAaSn8LBWqoHakOj3NGUjwAazp2QNsg0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=qjO1ANerf/QvdncGmVATgioNkdsgoRpPTjXbXJjAPWrU1CPyzoaMoALScUXWxDjeD 6nRluFiFGhplHoo4US0OroxMw8FbNN8I7GzeHqmtRkgQiYugNxyX3mfLpPSvfiogl7 7JLSctZcyYWR0LubrCov1GOnc1MUpMDy/3eyH3pM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727954AbfGVHsn (ORCPT ); Mon, 22 Jul 2019 03:48:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:32864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727164AbfGVHsm (ORCPT ); Mon, 22 Jul 2019 03:48:42 -0400 Received: from localhost.localdomain (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3AC992199C; Mon, 22 Jul 2019 07:48:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563781721; bh=H5CHHV0UF6FlAaSn8LBWqoHakOj3NGUjwAazp2QNsg0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xCerKnIQda79YHizJQQ3sqd4KdulwPP+ezU/7K0K22tjp+BxN4/X/WtJfhZVMVIgS rKjwbndl43anxmk5ZZcm3Y4OV1exJ/F8iP3kEvWAdWKACHILMCBzCdVvrwYNiQw7XM Rj2E51xE+Jv1hOADVQNIexarnOIrBeJV3ZoYEN1g= From: Masami Hiramatsu To: Catalin Marinas , Will Deacon Cc: mhiramat@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Naresh Kamboju , Dan Rue , Matt Hart , Anders Roxell , Daniel Diaz Subject: [PATCH v2 1/4] arm64: kprobes: Recover pstate.D in single-step exception handler Date: Mon, 22 Jul 2019 16:48:36 +0900 Message-Id: <156378171555.12011.2511666394591527888.stgit@devnote2> X-Mailer: git-send-email 2.20.1 In-Reply-To: <156378170297.12011.17385386326930403235.stgit@devnote2> References: <156378170297.12011.17385386326930403235.stgit@devnote2> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On arm64, if a nested kprobes hit, it can crash the kernel with below error message. [ 152.118921] Unexpected kernel single-step exception at EL1 This is because commit 7419333fa15e ("arm64: kprobe: Always clear pstate.D in breakpoint exception handler") unmask pstate.D for doing single step but does not recover it after single step in the nested kprobes. That is correct *unless* any nested kprobes (single-stepping) runs inside other kprobes user handler. When the 1st kprobe hits, do_debug_exception() will be called. At this point, debug exception (= pstate.D) must be masked (=1). When the 2nd (nested) kprobe is hit before single-step of the first kprobe, it unmask debug exception (pstate.D = 0) and return. Then, when the 1st kprobe setting up single-step, it saves current DAIF, mask DAIF, enable single-step, and restore DAIF. However, since "D" flag in DAIF is cleared by the 2nd kprobe, the single-step exception happens soon after restoring DAIF. To solve this issue, this stores all DAIF bits and restore it after single stepping. Reported-by: Naresh Kamboju Fixes: commit 7419333fa15e ("arm64: kprobe: Always clear pstate.D in breakpoint exception handler") Signed-off-by: Masami Hiramatsu --- Changes in v2: - Save and restore all DAIF flags. - Operate pstate directly and remove spsr_set_debug_flag(). --- arch/arm64/kernel/probes/kprobes.c | 41 ++++++------------------------------ 1 file changed, 7 insertions(+), 34 deletions(-) diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c index bd5dfffca272..348e02b799a2 100644 --- a/arch/arm64/kernel/probes/kprobes.c +++ b/arch/arm64/kernel/probes/kprobes.c @@ -29,6 +29,8 @@ #include "decode-insn.h" +#define PSR_DAIF_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT) + DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL; DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk); @@ -167,33 +169,6 @@ static void __kprobes set_current_kprobe(struct kprobe *p) __this_cpu_write(current_kprobe, p); } -/* - * When PSTATE.D is set (masked), then software step exceptions can not be - * generated. - * SPSR's D bit shows the value of PSTATE.D immediately before the - * exception was taken. PSTATE.D is set while entering into any exception - * mode, however software clears it for any normal (none-debug-exception) - * mode in the exception entry. Therefore, when we are entering into kprobe - * breakpoint handler from any normal mode then SPSR.D bit is already - * cleared, however it is set when we are entering from any debug exception - * mode. - * Since we always need to generate single step exception after a kprobe - * breakpoint exception therefore we need to clear it unconditionally, when - * we become sure that the current breakpoint exception is for kprobe. - */ -static void __kprobes -spsr_set_debug_flag(struct pt_regs *regs, int mask) -{ - unsigned long spsr = regs->pstate; - - if (mask) - spsr |= PSR_D_BIT; - else - spsr &= ~PSR_D_BIT; - - regs->pstate = spsr; -} - /* * Interrupts need to be disabled before single-step mode is set, and not * reenabled until after single-step mode ends. @@ -205,17 +180,17 @@ spsr_set_debug_flag(struct pt_regs *regs, int mask) static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb, struct pt_regs *regs) { - kcb->saved_irqflag = regs->pstate; + kcb->saved_irqflag = regs->pstate & PSR_DAIF_MASK; regs->pstate |= PSR_I_BIT; + /* Unmask PSTATE.D for enabling software step exceptions. */ + regs->pstate &= ~PSR_D_BIT; } static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb, struct pt_regs *regs) { - if (kcb->saved_irqflag & PSR_I_BIT) - regs->pstate |= PSR_I_BIT; - else - regs->pstate &= ~PSR_I_BIT; + regs->pstate &= ~PSR_DAIF_MASK; + regs->pstate |= kcb->saved_irqflag; } static void __kprobes @@ -252,8 +227,6 @@ static void __kprobes setup_singlestep(struct kprobe *p, set_ss_context(kcb, slot); /* mark pending ss */ - spsr_set_debug_flag(regs, 0); - /* IRQs and single stepping do not mix well. */ kprobes_save_local_irqflag(kcb, regs); kernel_enable_single_step(regs);