From patchwork Wed Sep 2 09:29:04 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andre Przywara X-Patchwork-Id: 264413 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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, 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 B79ACC433E2 for ; Wed, 2 Sep 2020 09:29:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9138020FC3 for ; Wed, 2 Sep 2020 09:29:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726140AbgIBJ3R (ORCPT ); Wed, 2 Sep 2020 05:29:17 -0400 Received: from foss.arm.com ([217.140.110.172]:34218 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726226AbgIBJ3O (ORCPT ); Wed, 2 Sep 2020 05:29:14 -0400 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 1EB6931B; Wed, 2 Sep 2020 02:29:14 -0700 (PDT) Received: from donnerap.arm.com (donnerap.cambridge.arm.com [10.1.195.35]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6FB163F68F; Wed, 2 Sep 2020 02:29:13 -0700 (PDT) From: Andre Przywara To: stable@vger.kernel.org Cc: James Morse , Marc Zyngier , Catalin Marinas Subject: [PATCH stable v5.8 v2 2/2] KVM: arm64: Survive synchronous exceptions caused by AT instructions Date: Wed, 2 Sep 2020 10:29:04 +0100 Message-Id: <20200902092904.122477-3-andre.przywara@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200902092904.122477-1-andre.przywara@arm.com> References: <20200902092904.122477-1-andre.przywara@arm.com> Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: James Morse commit 88a84ccccb3966bcc3f309cdb76092a9892c0260 upstream. KVM doesn't expect any synchronous exceptions when executing, any such exception leads to a panic(). AT instructions access the guest page tables, and can cause a synchronous external abort to be taken. The arm-arm is unclear on what should happen if the guest has configured the hardware update of the access-flag, and a memory type in TCR_EL1 that does not support atomic operations. B2.2.6 "Possible implementation restrictions on using atomic instructions" from DDI0487F.a lists synchronous external abort as a possible behaviour of atomic instructions that target memory that isn't writeback cacheable, but the page table walker may behave differently. Make KVM robust to synchronous exceptions caused by AT instructions. Add a get_user() style helper for AT instructions that returns -EFAULT if an exception was generated. While KVM's version of the exception table mixes synchronous and asynchronous exceptions, only one of these can occur at each location. Re-enter the guest when the AT instructions take an exception on the assumption the guest will take the same exception. This isn't guaranteed to make forward progress, as the AT instructions may always walk the page tables, but guest execution may use the translation cached in the TLB. This isn't a problem, as since commit 5dcd0fdbb492 ("KVM: arm64: Defer guest entry when an asynchronous exception is pending"), KVM will return to the host to process IRQs allowing the rest of the system to keep running. Cc: stable@vger.kernel.org # v5.8 Signed-off-by: James Morse Reviewed-by: Marc Zyngier Signed-off-by: Catalin Marinas Signed-off-by: Andre Przywara --- arch/arm64/include/asm/kvm_asm.h | 28 ++++++++++++++++++++++++++++ arch/arm64/kvm/hyp/hyp-entry.S | 14 ++++++++++---- arch/arm64/kvm/hyp/switch.c | 8 ++++---- 3 files changed, 42 insertions(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h index 7f09543b7c9a..2eff49d81be2 100644 --- a/arch/arm64/include/asm/kvm_asm.h +++ b/arch/arm64/include/asm/kvm_asm.h @@ -121,6 +121,34 @@ extern char __smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ]; *__hyp_this_cpu_ptr(sym); \ }) +#define __KVM_EXTABLE(from, to) \ + " .pushsection __kvm_ex_table, \"a\"\n" \ + " .align 3\n" \ + " .long (" #from " - .), (" #to " - .)\n" \ + " .popsection\n" + + +#define __kvm_at(at_op, addr) \ +( { \ + int __kvm_at_err = 0; \ + u64 spsr, elr; \ + asm volatile( \ + " mrs %1, spsr_el2\n" \ + " mrs %2, elr_el2\n" \ + "1: at "at_op", %3\n" \ + " isb\n" \ + " b 9f\n" \ + "2: msr spsr_el2, %1\n" \ + " msr elr_el2, %2\n" \ + " mov %w0, %4\n" \ + "9:\n" \ + __KVM_EXTABLE(1b, 2b) \ + : "+r" (__kvm_at_err), "=&r" (spsr), "=&r" (elr) \ + : "r" (addr), "i" (-EFAULT)); \ + __kvm_at_err; \ +} ) + + #else /* __ASSEMBLY__ */ .macro hyp_adr_this_cpu reg, sym, tmp diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S index ca2e34063e59..741f7cbaeb79 100644 --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -166,13 +166,19 @@ el1_error: b __guest_exit el2_sync: - /* Check for illegal exception return, otherwise panic */ + /* Check for illegal exception return */ mrs x0, spsr_el2 + tbnz x0, #20, 1f - /* if this was something else, then panic! */ - tst x0, #PSR_IL_BIT - b.eq __hyp_panic + save_caller_saved_regs_vect + stp x29, x30, [sp, #-16]! + bl kvm_unexpected_el2_exception + ldp x29, x30, [sp], #16 + restore_caller_saved_regs_vect + + eret +1: /* Let's attempt a recovery from the illegal exception return */ get_vcpu_ptr x1, x0 mov x0, #ARM_EXCEPTION_IL diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c index 814f5f7119ed..97987342629a 100644 --- a/arch/arm64/kvm/hyp/switch.c +++ b/arch/arm64/kvm/hyp/switch.c @@ -303,10 +303,10 @@ static bool __hyp_text __translate_far_to_hpfar(u64 far, u64 *hpfar) * saved the guest context yet, and we may return early... */ par = read_sysreg(par_el1); - asm volatile("at s1e1r, %0" : : "r" (far)); - isb(); - - tmp = read_sysreg(par_el1); + if (!__kvm_at("s1e1r", far)) + tmp = read_sysreg(par_el1); + else + tmp = SYS_PAR_EL1_F; /* back to the guest */ write_sysreg(par, par_el1); if (unlikely(tmp & SYS_PAR_EL1_F))