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,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 B4D8BC433DF for ; Thu, 2 Jul 2020 21:26:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 941F7217BA for ; Thu, 2 Jul 2020 21:26:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593725193; bh=ZU5bN8TFKsBpG7ffBzcNwKzyng+zc2xtVawCNyfX2Do=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ZX588FSikClIQfDiKt6rD7moMZ2g6r6HjdGsoOg3L6ZA+wg6GtP/HoZWRkiVCZgYJ 8Nze4j+a1MqdiUKtM9A/cGv+XxZ+5DqttT11oUxwAWNk2dW6wRWyiDPDgt5tkhrcH1 VsoUYII8QKEvHX46dom4NXU7KSfULSXvPjeHkgQs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726015AbgGBV0d (ORCPT ); Thu, 2 Jul 2020 17:26:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:38430 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725937AbgGBV0c (ORCPT ); Thu, 2 Jul 2020 17:26:32 -0400 Received: from localhost.localdomain (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 7B27E212CC; Thu, 2 Jul 2020 21:26:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593725191; bh=ZU5bN8TFKsBpG7ffBzcNwKzyng+zc2xtVawCNyfX2Do=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OMSPuUXRbnym3iADurHhuu+tR2caxUYLK0/6QPliNF1ijzRUfTUD1wJPFHf7xnZ4P PEjI6e8dn617nAh+gA0cIyFUcECAN0uZLGQCskk77sZHPYHI+772GKxJ6v9k4VEFbu UIXFVXuBiB4PvnlR19iZG4Yie7lxPa9vj+E3/g9w= From: Will Deacon To: linux-arm-kernel@lists.infradead.org Cc: Will Deacon , kernel-team@android.com, Mark Rutland , Luis Machado , Keno Fischer , stable@vger.kernel.org Subject: [PATCH v2 3/4] arm64: Override SPSR.SS when single-stepping is enabled Date: Thu, 2 Jul 2020 22:26:17 +0100 Message-Id: <20200702212618.17800-4-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200702212618.17800-1-will@kernel.org> References: <20200702212618.17800-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Luis reports that, when reverse debugging with GDB, single-step does not function as expected on arm64: | I've noticed, under very specific conditions, that a PTRACE_SINGLESTEP | request by GDB won't execute the underlying instruction. As a consequence, | the PC doesn't move, but we return a SIGTRAP just like we would for a | regular successful PTRACE_SINGLESTEP request. The underlying problem is that when the CPU register state is restored as part of a reverse step, the SPSR.SS bit is cleared and so the hardware single-step state can transition to the "active-pending" state, causing an unexpected step exception to be taken immediately if a step operation is attempted. In hindsight, we probably shouldn't have exposed SPSR.SS in the pstate accessible by the GPR regset, but it's a bit late for that now. Instead, simply prevent userspace from configuring the bit to a value which is inconsistent with the TIF_SINGLESTEP state for the task being traced. Cc: Cc: Mark Rutland Cc: Keno Fischer Link: https://lore.kernel.org/r/1eed6d69-d53d-9657-1fc9-c089be07f98c@linaro.org Reported-by: Luis Machado Tested-by: Luis Machado Signed-off-by: Will Deacon --- arch/arm64/include/asm/debug-monitors.h | 2 ++ arch/arm64/kernel/debug-monitors.c | 20 ++++++++++++++++---- arch/arm64/kernel/ptrace.c | 4 ++-- 3 files changed, 20 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h index e5ceea213e39..0b298f48f5bf 100644 --- a/arch/arm64/include/asm/debug-monitors.h +++ b/arch/arm64/include/asm/debug-monitors.h @@ -109,6 +109,8 @@ void disable_debug_monitors(enum dbg_active_el el); void user_rewind_single_step(struct task_struct *task); void user_fastforward_single_step(struct task_struct *task); +void user_regs_reset_single_step(struct user_pt_regs *regs, + struct task_struct *task); void kernel_enable_single_step(struct pt_regs *regs); void kernel_disable_single_step(void); diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index 5df49366e9ab..91146c0a3691 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -141,17 +141,20 @@ postcore_initcall(debug_monitors_init); /* * Single step API and exception handling. */ -static void set_regs_spsr_ss(struct pt_regs *regs) +static void set_user_regs_spsr_ss(struct user_pt_regs *regs) { regs->pstate |= DBG_SPSR_SS; } -NOKPROBE_SYMBOL(set_regs_spsr_ss); +NOKPROBE_SYMBOL(set_user_regs_spsr_ss); -static void clear_regs_spsr_ss(struct pt_regs *regs) +static void clear_user_regs_spsr_ss(struct user_pt_regs *regs) { regs->pstate &= ~DBG_SPSR_SS; } -NOKPROBE_SYMBOL(clear_regs_spsr_ss); +NOKPROBE_SYMBOL(clear_user_regs_spsr_ss); + +#define set_regs_spsr_ss(r) set_user_regs_spsr_ss(&(r)->user_regs) +#define clear_regs_spsr_ss(r) clear_user_regs_spsr_ss(&(r)->user_regs) static DEFINE_SPINLOCK(debug_hook_lock); static LIST_HEAD(user_step_hook); @@ -402,6 +405,15 @@ void user_fastforward_single_step(struct task_struct *task) clear_regs_spsr_ss(task_pt_regs(task)); } +void user_regs_reset_single_step(struct user_pt_regs *regs, + struct task_struct *task) +{ + if (test_tsk_thread_flag(task, TIF_SINGLESTEP)) + set_user_regs_spsr_ss(regs); + else + clear_user_regs_spsr_ss(regs); +} + /* Kernel API */ void kernel_enable_single_step(struct pt_regs *regs) { diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 7b46caea1278..89fbee3991a2 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1959,8 +1959,8 @@ static int valid_native_regs(struct user_pt_regs *regs) */ int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task) { - if (!test_tsk_thread_flag(task, TIF_SINGLESTEP)) - regs->pstate &= ~DBG_SPSR_SS; + /* https://lore.kernel.org/lkml/20191118131525.GA4180@willie-the-truck */ + user_regs_reset_single_step(regs, task); if (is_compat_thread(task_thread_info(task))) return valid_compat_regs(regs); -- 2.27.0.212.ge8ba1cc988-goog