From patchwork Wed Nov 30 18:29:06 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: James Morse X-Patchwork-Id: 13060237 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4E19CC4321E for ; Wed, 30 Nov 2022 18:30:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version: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=ufR+jMDbHqDdBZ1Ft9vBynOf4Pt5l8ThrdIQEKS6QnA=; b=G97WjrGe3lxsdp T36D3LPb4mIC0sRWJdY0wwFCAvvB3S89dzZhgV77SroZLzFQ+teFUVsTv0RUVh5UMy0Lj4cG12EW3 lFwuFzVRktHTPizE+jK3BaEaONzbq/7VNjcwff31MrFl1d4jorAwuIQscdyHsGDIFCxP2qQcqDzsK XZw+mgoNbKkBvDMfFUQLkfHjJq5ECnJgQNhZCc71rG/i+MUDo3BQJ0qnWPX/SuOAKSJlCicPuwbDf QgEmU0Y6gNgPVtPK5ncLW5UbDTRuVpKG0oEDDWsExjm7ub6I3SLPxAiCt40d7JCc5ElUqY5MyB4rH VdXB2Z7dfjm3z87AEKwQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1p0Rq7-001ZRa-Gu; Wed, 30 Nov 2022 18:29:47 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1p0Rpj-001ZCz-Ds for linux-arm-kernel@lists.infradead.org; Wed, 30 Nov 2022 18:29:25 +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 B6974ED1; Wed, 30 Nov 2022 10:29:26 -0800 (PST) Received: from eglon.cambridge.arm.com (eglon.cambridge.arm.com [10.1.197.38]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5A70A3F73B; Wed, 30 Nov 2022 10:29:19 -0800 (PST) From: James Morse To: stable@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , James Morse , Sami Lee Subject: [stable:PATCH v4.19.267 1/2] arm64: Fix panic() when Spectre-v2 causes Spectre-BHB to re-allocate KVM vectors Date: Wed, 30 Nov 2022 18:29:06 +0000 Message-Id: <20221130182907.739150-2-james.morse@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20221130182907.739150-1-james.morse@arm.com> References: <20221130182907.739150-1-james.morse@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221130_102923_589969_D4D9F6A7 X-CRM114-Status: GOOD ( 16.07 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Sami reports that linux panic()s when resuming from suspend to RAM. This is because when CPUs are brought back online, they re-enable any necessary mitigations. The Spectre-v2 and Spectre-BHB mitigations interact as both need to done by KVM when exiting a guest. Slots KVM can use as vectors are allocated, and templates for the mitigation are patched into the vector. This fails if a new slot needs to be allocated once the kernel has finished booting as it is no-longer possible to modify KVM's vectors: | root@adam:/sys/devices/system/cpu/cpu1# echo 1 > online | Unable to handle kernel write to read-only memory at virtual add> | Mem abort info: | ESR = 0x9600004e | Exception class = DABT (current EL), IL = 32 bits | SET = 0, FnV = 0 | EA = 0, S1PTW = 0 | Data abort info: | ISV = 0, ISS = 0x0000004e | CM = 0, WnR = 1 | swapper pgtable: 4k pages, 48-bit VAs, pgdp = 000000000f07a71c | [ffff800000b4b800] pgd=00000009ffff8803, pud=00000009ffff7803, p> | Internal error: Oops: 9600004e [#1] PREEMPT SMP | Modules linked in: | Process swapper/1 (pid: 0, stack limit = 0x0000000063153c53) | CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.19.252-dirty #14 | Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno De> | pstate: 000001c5 (nzcv dAIF -PAN -UAO) | pc : __memcpy+0x48/0x180 | lr : __copy_hyp_vect_bpi+0x64/0x90 | Call trace: | __memcpy+0x48/0x180 | kvm_setup_bhb_slot+0x204/0x2a8 | spectre_bhb_enable_mitigation+0x1b8/0x1d0 | __verify_local_cpu_caps+0x54/0xf0 | check_local_cpu_capabilities+0xc4/0x184 | secondary_start_kernel+0xb0/0x170 | Code: b8404423 b80044c3 36180064 f8408423 (f80084c3) | ---[ end trace 859bcacb09555348 ]--- | Kernel panic - not syncing: Attempted to kill the idle task! | SMP: stopping secondary CPUs | Kernel Offset: disabled | CPU features: 0x10,25806086 | Memory Limit: none | ---[ end Kernel panic - not syncing: Attempted to kill the idle ] This is only a problem on platforms where there is only one CPU that is vulnerable to both Spectre-v2 and Spectre-BHB. The Spectre-v2 mitigation identifies the slot it can re-use by the CPU's 'fn'. It unconditionally writes the slot number and 'template_start' pointer. The Spectre-BHB mitigation identifies slots it can re-use by the CPU's template_start pointer, which was previously clobbered by the Spectre-v2 mitigation. When there is only one CPU that is vulnerable to both issues, this causes Spectre-v2 to try to allocate a new slot, which fails. Change both mitigations to check whether they are changing the slot this CPU uses before writing the percpu variables again. This issue only exists in the stable backports for Spectre-BHB which have to use totally different infrastructure to mainline. Reported-by: Sami Lee Fixes: c20d55174479 ("arm64: Mitigate spectre style branch history side channels") Signed-off-by: James Morse --- arch/arm64/kernel/cpu_errata.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index 5435550d1c9b..9418d2257b9a 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -142,9 +142,12 @@ static void install_bp_hardening_cb(bp_hardening_cb_t fn, __copy_hyp_vect_bpi(slot, hyp_vecs_start, hyp_vecs_end); } - __this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot); - __this_cpu_write(bp_hardening_data.fn, fn); - __this_cpu_write(bp_hardening_data.template_start, hyp_vecs_start); + if (fn != __this_cpu_read(bp_hardening_data.fn)) { + __this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot); + __this_cpu_write(bp_hardening_data.fn, fn); + __this_cpu_write(bp_hardening_data.template_start, + hyp_vecs_start); + } spin_unlock(&bp_lock); } #else @@ -1203,8 +1206,11 @@ static void kvm_setup_bhb_slot(const char *hyp_vecs_start) __copy_hyp_vect_bpi(slot, hyp_vecs_start, hyp_vecs_end); } - __this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot); - __this_cpu_write(bp_hardening_data.template_start, hyp_vecs_start); + if (hyp_vecs_start != __this_cpu_read(bp_hardening_data.template_start)) { + __this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot); + __this_cpu_write(bp_hardening_data.template_start, + hyp_vecs_start); + } spin_unlock(&bp_lock); } #else