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dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.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:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version: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=QLK5IDC5wJ9QUKjijjQdfHgL+FyUWmbRmGFMMtXUY7A=; b=J3XQ6eEAqz0Vt4CxCGupyloNq qlMwUBsxnsIpO2VTQbiTYepAo5iImxMl/Jp5msN2N5ncC0XXRgrtd4CfYa1GobtAX/B3Fowb/UPlv EeYzn81GfE8PInN0IZ1arHqgh593S5UxMBfvrS623qhyLGuIsnEj2ZqZvIZWPvNrbQxjYKNuW2Ltv JraTBtaGwjDsxvTrgEeazvcgUUksUSBc4MA3hBZr32mPekCFRT5ujuKjtsX1fmMGv/bVal0UtXhR0 GXrr6hYr2+DdtlNtpfVAF4kOV6R6xmz2zAeGrs05SxkpeYbqwms0JGxxrTH/i/7FxlEmLDJrXlxFT J80xsXYYg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jr6j4-0004fe-0E; Thu, 02 Jul 2020 21:26:34 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jr6j0-0004eS-Im for linux-arm-kernel@lists.infradead.org; Thu, 02 Jul 2020 21:26:31 +0000 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 C609920CC7; Thu, 2 Jul 2020 21:26:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593725190; bh=vACqoqs/To7f7QuZMDFOJ9SJPPnkguwTilxNLqLBM84=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2lLiAMOE1kluw9230csObSBBYzK7aV3Bg6DjHvH13i9kwucs+dCFeAhdQPyPm8DtB XihU7Kd0JcS6ECUC/QJzoQt4A8MZercROV57qZh6egZ1gwu2hBGzBs1e4veBcAI5La mu1ZXKkMBBgcRHZxhL7MkHf9qOp92zDjtxCChUYc= From: Will Deacon To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 2/4] arm64: ptrace: Consistently use pseudo-singlestep exceptions Date: Thu, 2 Jul 2020 22:26:16 +0100 Message-Id: <20200702212618.17800-3-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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200702_172630_787771_0A38AE34 X-CRM114-Status: GOOD ( 19.51 ) X-Spam-Score: -5.2 (-----) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (-5.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -5.0 RCVD_IN_DNSWL_HI RBL: Sender listed at https://www.dnswl.org/, high trust [198.145.29.99 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain -0.0 DKIMWL_WL_HIGH DKIMwl.org - Whitelisted High sender 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 , Luis Machado , Will Deacon , stable@vger.kernel.org, Keno Fischer , kernel-team@android.com Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Although the arm64 single-step state machine can be fast-forwarded in cases where we wish to generate a SIGTRAP without actually executing an instruction, this has two major limitations outside of simply skipping an instruction due to emulation. 1. Stepping out of a ptrace signal stop into a signal handler where SIGTRAP is blocked. Fast-forwarding the stepping state machine in this case will result in a forced SIGTRAP, with the handler reset to SIG_DFL. 2. The hardware implicitly fast-forwards the state machine when executing an SVC instruction for issuing a system call. This can interact badly with subsequent ptrace stops signalled during the execution of the system call (e.g. SYSCALL_EXIT or seccomp traps), as they may corrupt the stepping state by updating the PSTATE for the tracee. Resolve both of these issues by injecting a pseudo-singlestep exception on entry to a signal handler and also on return to userspace following a system call. Cc: Cc: Mark Rutland Cc: Luis Machado Reported-by: Keno Fischer Signed-off-by: Will Deacon --- arch/arm64/include/asm/thread_info.h | 1 + arch/arm64/kernel/ptrace.c | 25 +++++++++++++++++++------ arch/arm64/kernel/signal.c | 11 ++--------- arch/arm64/kernel/syscall.c | 2 +- 4 files changed, 23 insertions(+), 16 deletions(-) diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h index 6ea8b6a26ae9..5e784e16ee89 100644 --- a/arch/arm64/include/asm/thread_info.h +++ b/arch/arm64/include/asm/thread_info.h @@ -93,6 +93,7 @@ void arch_release_task_struct(struct task_struct *tsk); #define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU) #define _TIF_UPROBE (1 << TIF_UPROBE) #define _TIF_FSCHECK (1 << TIF_FSCHECK) +#define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP) #define _TIF_32BIT (1 << TIF_32BIT) #define _TIF_SVE (1 << TIF_SVE) diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index d71795dc3dbd..7b46caea1278 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1830,12 +1830,23 @@ static void tracehook_report_syscall(struct pt_regs *regs, saved_reg = regs->regs[regno]; regs->regs[regno] = dir; - if (dir == PTRACE_SYSCALL_EXIT) + if (dir == PTRACE_SYSCALL_ENTER) { + if (tracehook_report_syscall_entry(regs)) + forget_syscall(regs); + regs->regs[regno] = saved_reg; + } else if (!test_thread_flag(TIF_SINGLESTEP)) { tracehook_report_syscall_exit(regs, 0); - else if (tracehook_report_syscall_entry(regs)) - forget_syscall(regs); + regs->regs[regno] = saved_reg; + } else { + regs->regs[regno] = saved_reg; - regs->regs[regno] = saved_reg; + /* + * Signal a pseudo-step exception since we are stepping but + * tracer modifications to the registers may have rewound the + * state machine. + */ + tracehook_report_syscall_exit(regs, 1); + } } int syscall_trace_enter(struct pt_regs *regs) @@ -1863,12 +1874,14 @@ int syscall_trace_enter(struct pt_regs *regs) void syscall_trace_exit(struct pt_regs *regs) { + unsigned long flags = READ_ONCE(current_thread_info()->flags); + audit_syscall_exit(regs); - if (test_thread_flag(TIF_SYSCALL_TRACEPOINT)) + if (flags & _TIF_SYSCALL_TRACEPOINT) trace_sys_exit(regs, regs_return_value(regs)); - if (test_thread_flag(TIF_SYSCALL_TRACE)) + if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP)) tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT); rseq_syscall(regs); diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 801d56cdf701..3b4f31f35e45 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -800,7 +800,6 @@ static void setup_restart_syscall(struct pt_regs *regs) */ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs) { - struct task_struct *tsk = current; sigset_t *oldset = sigmask_to_save(); int usig = ksig->sig; int ret; @@ -824,14 +823,8 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs) */ ret |= !valid_user_regs(®s->user_regs, current); - /* - * Fast forward the stepping logic so we step into the signal - * handler. - */ - if (!ret) - user_fastforward_single_step(tsk); - - signal_setup_done(ret, ksig, 0); + /* Step into the signal handler if we are stepping */ + signal_setup_done(ret, ksig, test_thread_flag(TIF_SINGLESTEP)); } /* diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index 5f5b868292f5..7c14466a12af 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -139,7 +139,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) { local_daif_mask(); flags = current_thread_info()->flags; - if (!has_syscall_work(flags)) { + if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) { /* * We're off to userspace, where interrupts are * always enabled after we restore the flags from