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=-17.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,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 5FF29C433ED for ; Thu, 20 May 2021 11:53:09 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 DF6F261006 for ; Thu, 20 May 2021 11:53:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DF6F261006 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=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:MIME-Version:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id: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=4+SCFbL5e2icVNOvcwPPvSE2jFF59nCOkGhkPbzTSrY=; b=fUJvFXsKabGaGyhbyCph+aMPcJ 7Ahn7/iCz5v5bYdeG40xgBS1AOoorhY8jCPNgNge003angcCLii7RFi1KW6Cga12tAdcHagJjh435 +jwUCXlyo8v0c3nHGtocGWSVPOolhyPIbyzXFJf/eZVsApQ3Z/kB1PwU7cA7AOGXm4sTqa/trc6NL i3tNTCxdIntL77Ka9zvVCfDy8QEca/I9zot7aNIWesrI+jthMtIaoyMi95XcPZ++UAGG6Uj5eabC7 ax4C9W6dkr5YW7JrQ/g/cOBl3oTJClrQe7kOMlZNU5iWxrQ2kzC01YSVHiRj/mGIlg4CmC1KkuYJ+ +ScuRhaA==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ljhDB-000cPV-T9; Thu, 20 May 2021 11:51:35 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ljhCR-000cAH-AC for linux-arm-kernel@desiato.infradead.org; Thu, 20 May 2021 11:50:47 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=References:In-Reply-To:Message-Id: Date:Subject:Cc:To:From:Sender:Reply-To:MIME-Version:Content-Type: Content-Transfer-Encoding:Content-ID:Content-Description; bh=XE6nCwT5eD+MgbEiRhpdLZu7QiYOG6ovctlY2VKCLkQ=; b=mbAGVCv08b25GtSnElqwZTmOcG 3lDnBpNdJNhIPt8X9cAwmDprKTDgNnIe+/bMi/jtJ/6+1cp+wPzNKMGGB0V7aYotbdEiAVLkf3pyZ uGz6c9vzqMZRYb+GjW350RC6A2/ny+1494aWyBJItFeAw7IW2EFdgBF3pXJt2YCpTrQM1Ikigp/a8 O4O+5H6xaQIHptADe6ph3b3KKfNIvAlWR7YbxS0rB0IOgFgp1gucLLVleglT+GgN+OWQO/JHUKfk2 g8KsTM1Hz7t3L08UdkY2uZF0xySRSXSl4UjyCLdgM7ltyR4og+IeI6nM5iHQN3UGhcA1yFzPhXaDL I1aXRiEQ==; Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1ljhCO-00GH5L-61 for linux-arm-kernel@lists.infradead.org; Thu, 20 May 2021 11:50:45 +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 98AEF101E; Thu, 20 May 2021 04:50:43 -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 4897C3F73D; Thu, 20 May 2021 04:50:42 -0700 (PDT) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, broonie@kernel.org, catalin.marinas@arm.com, james.morse@arm.com, madvenka@linux.microsoft.com, mark.rutland@arm.com, maz@kernel.org, suzuki.poulose@arm.com, will@kernel.org Subject: [PATCH 1/6] arm64: Implement stack trace termination record Date: Thu, 20 May 2021 12:50:26 +0100 Message-Id: <20210520115031.18509-2-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20210520115031.18509-1-mark.rutland@arm.com> References: <20210520115031.18509-1-mark.rutland@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210520_045044_343999_60E6FE7B X-CRM114-Status: GOOD ( 23.66 ) 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: , 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 From: "Madhavan T. Venkataraman" Reliable stacktracing requires that we identify when a stacktrace is terminated early. We can do this by ensuring all tasks have a final frame record at a known location on their task stack, and checking that this is the final frame record in the chain. We'd like to use task_pt_regs(task)->stackframe as the final frame record, as this is already setup upon exception entry from EL0. For kernel tasks we need to consistently reserve the pt_regs and point x29 at this, which we can do with small changes to __primary_switched, __secondary_switched, and copy_process(). Since the final frame record must be at a specific location, we must create the final frame record in __primary_switched and __secondary_switched rather than leaving this to start_kernel and secondary_start_kernel. Thus, __primary_switched and __secondary_switched will now show up in stacktraces for the idle tasks. Since the final frame record is now identified by its location rather than by its contents, we identify it at the start of unwind_frame(), before we read any values from it. External debuggers may terminate the stack trace when FP == 0. In the pt_regs->stackframe, the PC is 0 as well. So, stack traces taken in the debugger may print an extra record 0x0 at the end. While this is not pretty, this does not do any harm. This is a small price to pay for having reliable stack trace termination in the kernel. That said, gdb does not show the extra record probably because it uses DWARF and not frame pointers for stack traces. Signed-off-by: Madhavan T. Venkataraman Reviewed-by: Mark Brown [Mark: rebase, use ASM_BUG(), update comments, update commit message] Signed-off-by: Mark Rutland --- arch/arm64/kernel/entry.S | 2 +- arch/arm64/kernel/head.S | 25 +++++++++++++++++++------ arch/arm64/kernel/process.c | 5 +++++ arch/arm64/kernel/stacktrace.c | 16 +++++++--------- 4 files changed, 32 insertions(+), 16 deletions(-) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 3513984a88bd..294f24e16fee 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -285,7 +285,7 @@ alternative_else_nop_endif stp lr, x21, [sp, #S_LR] /* - * For exceptions from EL0, create a terminal frame record. + * For exceptions from EL0, create a final frame record. * For exceptions from EL1, create a synthetic frame record so the * interrupted code shows up in the backtrace. */ diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 96873dfa67fd..cc2d45d54838 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -393,6 +394,18 @@ SYM_FUNC_START_LOCAL(__create_page_tables) ret x28 SYM_FUNC_END(__create_page_tables) + /* + * Create a final frame record at task_pt_regs(current)->stackframe, so + * that the unwinder can identify the final frame record of any task by + * its location in the task stack. We reserve the entire pt_regs space + * for consistency with user tasks and kthreads. + */ + .macro setup_final_frame + sub sp, sp, #PT_REGS_SIZE + stp xzr, xzr, [sp, #S_STACKFRAME] + add x29, sp, #S_STACKFRAME + .endm + /* * The following fragment of code is executed with the MMU enabled. * @@ -447,9 +460,9 @@ SYM_FUNC_START_LOCAL(__primary_switched) #endif bl switch_to_vhe // Prefer VHE if possible add sp, sp, #16 - mov x29, #0 - mov x30, #0 - b start_kernel + setup_final_frame + bl start_kernel + ASM_BUG() SYM_FUNC_END(__primary_switched) .pushsection ".rodata", "a" @@ -639,14 +652,14 @@ SYM_FUNC_START_LOCAL(__secondary_switched) cbz x2, __secondary_too_slow msr sp_el0, x2 scs_load x2, x3 - mov x29, #0 - mov x30, #0 + setup_final_frame #ifdef CONFIG_ARM64_PTR_AUTH ptrauth_keys_init_cpu x2, x3, x4, x5 #endif - b secondary_start_kernel + bl secondary_start_kernel + ASM_BUG() SYM_FUNC_END(__secondary_switched) SYM_FUNC_START_LOCAL(__secondary_too_slow) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index b4bb67f17a2c..8928fba54e4b 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -435,6 +435,11 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, } p->thread.cpu_context.pc = (unsigned long)ret_from_fork; p->thread.cpu_context.sp = (unsigned long)childregs; + /* + * For the benefit of the unwinder, set up childregs->stackframe + * as the final frame for the new task. + */ + p->thread.cpu_context.fp = (unsigned long)childregs->stackframe; ptrace_hw_copy_thread(p); diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index de07147a7926..36cf05d5eb9e 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -68,12 +68,16 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) unsigned long fp = frame->fp; struct stack_info info; - if (fp & 0xf) - return -EINVAL; - if (!tsk) tsk = current; + /* Final frame; nothing to unwind */ + if (fp == (unsigned long)task_pt_regs(tsk)->stackframe) + return -ENOENT; + + if (fp & 0xf) + return -EINVAL; + if (!on_accessible_stack(tsk, fp, &info)) return -EINVAL; @@ -128,12 +132,6 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) frame->pc = ptrauth_strip_insn_pac(frame->pc); - /* - * This is a terminal record, so we have finished unwinding. - */ - if (!frame->fp && !frame->pc) - return -ENOENT; - return 0; } NOKPROBE_SYMBOL(unwind_frame); -- 2.11.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel