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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE30AC433F5 for ; Fri, 8 Apr 2022 16:08:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237934AbiDHQKQ (ORCPT ); Fri, 8 Apr 2022 12:10:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44714 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237917AbiDHQKK (ORCPT ); Fri, 8 Apr 2022 12:10:10 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4A78D347FA0 for ; Fri, 8 Apr 2022 09:08:06 -0700 (PDT) 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 F382B113E; Fri, 8 Apr 2022 09:08:05 -0700 (PDT) Received: from [10.1.196.218] (eglon.cambridge.arm.com [10.1.196.218]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 034B13F73B; Fri, 8 Apr 2022 09:08:04 -0700 (PDT) Subject: Re: arm64 spectre-bhb backports break boot on stable kernels <= v5.4 To: Will Deacon , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, maz@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com References: <20220408120041.GB27685@willie-the-truck> From: James Morse Message-ID: <1a44f42c-0391-7428-ac85-1e27aaf0be14@arm.com> Date: Fri, 8 Apr 2022 17:08:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20220408120041.GB27685@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Will, On 08/04/2022 13:00, Will Deacon wrote: > Booting stable kernels <= v5.4 on arm64 with CONFIG_HARDEN_BRANCH_PREDICTOR=n > results in a NULL pointer dereference during boot due to kvm_get_hyp_vector() > dereferencing a NULL pointer from arm64_get_bp_hardening_data(): > > [ 2.384444] Internal error: Oops: 96000004 [#1] PREEMPT SMP > [ 2.384461] pstate: 20400085 (nzCv daIf +PAN -UAO) > [ 2.384472] pc : cpu_hyp_reinit+0x114/0x30c > [ 2.384476] lr : cpu_hyp_reinit+0x80/0x30c > [ 2.384477] sp : ffff800010013e20 > [ 2.384479] x29: ffff800010013e20 x28: ffff0000df033f00 > [ 2.384484] x27: ffff800011caa000 x26: ffff0000de58e000 > [ 2.384487] x25: ffff800011e57000 x24: ffff800011caad90 > [ 2.384490] x23: ffff800011c778e0 x22: ffff800011a56000 > [ 2.384494] x21: ffff800011a56000 x20: 0000b471121a6000 > [ 2.384497] x19: 00000000de588000 x18: 0000000000000000 > [ 2.384500] x17: 0000000000000000 x16: 0000000000000400 > [ 2.384503] x15: 0000000000001000 x14: 00000000000007f2 > [ 2.384507] x13: 0000000000000004 x12: 0000000000000002 > [ 2.384510] x11: 0000000000000000 x10: 00000000121a6000 > [ 2.384513] x9 : ffff800011c77fd8 x8 : 0000000000000010 > [ 2.384516] x7 : 4f422effff306b64 x6 : 0000008080000000 > [ 2.384519] x5 : 0000008080000000 x4 : ffff800011fabc94 > [ 2.384522] x3 : ffff800011f5bde0 x2 : 0000000000000001 > [ 2.384526] x1 : 00000000121a0000 x0 : ffff8000118f962d > [ 2.384529] Call trace: > [ 2.384533] cpu_hyp_reinit+0x114/0x30c > [ 2.384537] _kvm_arch_hardware_enable+0x30/0x54 > [ 2.384541] flush_smp_call_function_queue+0xe4/0x154 > [ 2.384544] generic_smp_call_function_single_interrupt+0x10/0x18 > [ 2.384549] ipi_handler+0x170/0x2b0 > [ 2.384555] handle_percpu_devid_fasteoi_ipi+0x120/0x1cc > [ 2.384560] __handle_domain_irq+0x9c/0xf4 > [ 2.384563] gic_handle_irq+0x6c/0xe4 > [ 2.384566] el1_irq+0xf0/0x1c0 > [ 2.384570] arch_cpu_idle+0x28/0x44 > [ 2.384574] do_idle+0x100/0x2a8 > [ 2.384577] cpu_startup_entry+0x20/0x24 > [ 2.384581] secondary_start_kernel+0x1b0/0x1cc > [ 2.384589] Code: b9469d08 7100011f 540003ad 52800208 (f9400108) > [ 2.384600] ---[ end trace 266d08dbf96ff143 ]--- > [ 2.385171] Kernel panic - not syncing: Fatal exception in interrupt Yikes! Interesting to know that stuff behind CONFIG_EXPERT has someone who cares about it. (I was going to propose dropping the Kconfig option after a while). > The faulting load is the access to 'data->template_start', for which the > compiler emits the hilarious: > > mov w8, #0x10 > ldr x8, [x8] This is nasal-daemon territory, so I guess the compiler can do whatever it likes. > I can bodge this as below (untested), but it's pretty grotty. I wanted to keep the detection code even if the feature is disabled so the sysfs reporting is always correct. > Please can you take a look? Ugh, arm64_get_bp_hardening_data() returns NULL with that Kconfig setup. For v5.4, this fixes it for me: --------------------%<-------------------- diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h index 78d110667c0c..ffe0aad96b17 100644 --- a/arch/arm64/include/asm/kvm_mmu.h +++ b/arch/arm64/include/asm/kvm_mmu.h @@ -479,7 +479,8 @@ static inline void *kvm_get_hyp_vector(void) int slot = -1; if ((cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR) || - cpus_have_const_cap(ARM64_SPECTRE_BHB)) && data->template_start) { + cpus_have_const_cap(ARM64_SPECTRE_BHB)) && + data && data->template_start) { vect = kern_hyp_va(kvm_ksym_ref(__bp_harden_hyp_vecs_start)); slot = data->hyp_vectors_slot; } --------------------%<-------------------- I'll check the other versions and post patches to the stable list. Earlier stable backports grew a dependency between these features as it wasn't possible to unpick the dependencies. Thanks, James